JouThe International, Interdisciplinary Society Devotedr to Ocean andnal Marine Engineering, Science, and Policy Volume 47 Number 3 May/June 2013
Focus on DeepStar® Global Deepwater Technology Development OCEANS‘13 CONFERENCE
EXHIBITORS HIGHLIGHTS INCLUDE: Good spaces are still left, but going fast! • Twelve Co-participating Societies • Academic Host: Scripps Institution ATTENDEES Registration opens May 20! of Oceanography/UCSD • Over 250 exhibits in two halls, plus Academic Row • Opening Plenary with Ocean VIPs • Extensive technical and scientific tracks and sessions • Ultra-Deep Ocean Track with renowned presenters • Tutorials with college credit • Student Opportunities: Discounted Rates, Session Chairs, Poster Competition • Golf Tournament • Underwater Film Festival on two nights • Gala on the Carrier U.S.S. Midway • A celebration of the MTS 50th Anniversary • STEM Educators Workshop
AcAdemic SponSor:
EXHIBIT SPACE VISIT US ONLINE Space is filling up, but many good locations are still available. OCEANS13MTSIEEESANDIEGO.ORG Visit the interactive Oceans 2013 Exhibit Hall Floor Plan at: oceans13mtsieeesandiego.org/exhibitor/floorplan and pick your spot. Or contact Sue Kingston, IEEE Exhibits Manager, for more information. LIKE US ON FACEBOOK: e-mail: [email protected] • office: 1 (310) 937-1006 • cell 1 (310) 699-2609 /Oceans2013 Volume 47, Number 3, May/June 2013 Focus on DeepStar® Global Deepwater Technology Development
In This Issue Front Cover: DeepStar® cover graphic, artwork, and logo is a registered trademark of Chevron Intellectual Property LLC. Focus on DeepStar 72 Back Cover: All images can be found within this issue. 5 Anchor Drop Tests for a Submarine Top row (l-r): Schmidt et al., Figure 6; Cui, Figure 4; 2nd row: DeepStar®: 22 Years of Success Power-Cable Protector Vedachalam et al., Figure 4; 3rd row (l-r): Yoon & Na, Figure 3; Vedachalam et al., Figure 15; Cooper et al., Figure 1; DeepStar: A Global Deepwater Han-Sam Yoon, Won-Bae Na Bottom row (l-r): Jacobson, Figure 3; Peirano, Figure 2. Technology Development Program Greg Kusinski, Art J. Schroeder, Jr., 81 James E. Chitwood Elements of Underwater Glider Performance and Stability 13 Shuangshuang Fan, Craig Woolsey DeepStar 11304: Laying the Groundwork for AUV Standards for 99 Deepwater Fields Analysis of Underwater Acoustic John Jacobson, Pierce Cohen, Amin Nasr, Communication Channels Art J. Schroeder, Jr., Greg Kusinski Sadia Ahmed, Huseyin Arslan 19 118 DeepStar Metocean Studies: 15 years Wrecks on the Bottom: Useful, of Discovery Ecological Sentinels? Cortis Cooper, Tom Mitchell, Andrea Peirano George Forristall, James Stear 27 Recent Development in IR Sensor Technology for Monitoring Subsea Text: SPi Methane Discharge Cover and Graphics: Mark Schmidt, Peter Linke, Daniel Esser Michele A. Danoff, Graphics By Design The Marine Technology Society Journal (ISSN 0025-3324) is published by the Marine Technology General Papers Society, Inc., 1100 H Street NW, Suite LL-100 37 Washington, DC 20005 Development of the Jiaolong Deep Subscription Prices (all prices include shipping): Manned Submersible MTS members can purchase the printed Journal for Weicheng Cui $32 domestic and $110 international. Non-members and library subscriptions are $435 online only (includes 13 years of archives); $460 for online with print (includes 12 years of 55 archives); $135 print only within the U.S. and Canada, Reliability-Centered Development of $200 print only international. Single-issue (hardcopy) is $20 plus $7.50 S&H (domestic), $24.50 S&H Deep Water ROV ROSUB 6000 (international); Pay-per-view (worldwide): $15/article. Vedachalam Narayanaswamy, Postage for periodicals is paid at Washington, DC Ramesh Raju, Muthukumaran Durairaj, and additional mailing offices. Aarthi Ananthapadmanabhan, POSTMASTER: Subramanian Annamalai, Please send address changes to: Gidugu Ananada Ramadass, Marine Technology Society Journal Malayath Aravindakshan Atmanand 1100 H Street NW, Suite LL-100 Washington, DC 20005 Tel: (202) 717-8705; Fax: (202) 347-4305
Copyright © 2013 Marine Technology Society, Inc. Marine Technology Society Officers
BOARD OF DIRECTORS PROFESSIONAL COMMITTEES James Marsh President Industry and Technology University of Hawaii Drew Michael Buoy Technology Ocean Observing Systems ROV Technologies, Inc. Dr. Walter Paul Donna Kocak President-elect Woods Hole Oceanographic Institution HARRIS Corporation Richard W. Spinrad Cables and Connectors Ocean Pollution Oregon State University Vacant Ryan Morton Immediate Past President Deepwater Field Development Technology Anadarko Petroleum Jerry Boatman Dr. Benton Baugh Renewable Energy QinetiQ North America – Technology Solutions Radoil, Inc. Maggie L. Merrill Group Diving Marine Marketing Services and New England VP—Section Affairs Michael Lombardi MREC at UMass Dartmouth Lisa Medeiros Ocean Opportunity Kenneth Baldwin Geospace Offshore Cables Michael Max University of New Hampshire VP—Education and Research Hydrate Energy International LLC Jill Zande Dynamic Positioning STUDENT SECTIONS MATE Center Howard Shatto Alpena Community College VP—Industry and Technology Shatto Engineering Counselor: TBD Raymond Toll Manned Underwater Vehicles Brigham Young University Computer Sciences Corporation William Kohnen Counselor: TBD VP—Publications HYDROSPACE Group College of William & Mary Donna Kocak Moorings Counselor: Heather MacDonald HARRIS Corporation Jack Rowley Dalhousie University Treasurer and VP—Budget and Finance SAIC Counselor: Tejana Ross, Ph.D. Debra Kill Oceanographic Instrumentation Duke University International Submarine Engineering Dr. Carol Janzen Counselor: Douglas Nowacek, Ph.D. VP—Government and Public Affairs Sea-Bird Electronics, Inc. Florida Atlantic University Justin Manley Offshore Structures Counselor: Douglas A. Briggs, Ph.D. Teledyne Benthos Dr. Peter W. Marshall Florida Institute of Technology MHP Systems Engineering Counselor: Stephen Wood, Ph.D., P.E. SECTIONS Remotely Operated Vehicles Long Beach City College Canadian Maritime Chuck Richards Counselor: Scott Fraser Vacant C.A. Richards and Associates, Inc. Marine Institute (MI) Great Lakes Ropes and Tension Members Counselor: TBD TBD Evan Zimmerman Massachusetts Institute of Technology Gulf Coast Delmar Systems, Inc. Counselor: Alexandra Techet, Ph.D. Laurie Jugan Seafloor Engineering Memorial University (MUN) Consultant Craig Etka Counselor: TBD Hampton Roads Scorpio Ventures, LLC Monterey Peninsula College/Hartnell College Raymond Toll Underwater Imaging Counselor: Jeremy R. Hertzberg Computer Sciences Corporation Dr. Fraser Dalgleish Northeastern University Hawaii Harbor Branch Oceanographic Institute Counselor: Joseph Ayers, Ph.D. Stu Burley Unmanned Maritime Vehicles Oregon State University Strategic Theories Unlimited Rafael Mandujano Counselor: R. Kipp Shearman Houston Vehicle Control Technologies, Inc. Texas A&M University—College Station Aimee Marsh Counselor: Robert Randall, Ph.D. EIC Education and Research Texas A&M—Corpus Christi Japan Marine Archaeology Counselor: Dugan Um, Ph.D. Prof. Toshitsugu Sakou Dan Warren Texas A&M University—Galveston Tokai University C & C Technologies Counselor: David Talent, Ph.D. Mid-Gulf Coast-Florida Marine Education United States Naval Academy Erica Moulton Erica Moulton Counselor: Cmdr. David J. Robillard MATE MATE Center University of Hawaii Monterey Marine Geodetic Information Systems Counselor: Dr. Reza Ghorbani Jill Zande Dave Zilkoski University of Houston MATE Center NOAA Counselors: Raresh Pascali, P.E., New England Marine Materials Chuck Richards Chris Jakubiak Capt. Dennis “Mike” Egan University of North Carolina—Charlotte UMASS Dartmouth-SMAST EESS, LLC Counselor: James Conrad, Ph.D. Norway Ocean Exploration University of Southern Mississippi TBD Shane Zigler Counselor: Stephen Howden, Ph.D. Newfoundland and Labrador OceanGate, Inc. University of Washington Gary Dinn Physical Oceanography/Meteorology Counselor: Rick Rupan Memorial University Dr. Richard L. Crout Webb Institute Oregon National Data Buoy Center Counselor: Matthew Werner Jeremy Childress Remote Sensing Oregon State University Ryan Vandermeulen HONORARY MEMBERS College of Oceanic & Atmospheric Sciences University of Southern Mississippi †Robert B. Abel Puget Sound †Charles H. Bussmann Fritz Stahr Government and Public Affairs John C. Calhoun, Jr. University of Washington Marine Law and Policy John P. Craven San Diego Vacant †Paul M. Fye David Velasco Marine Mineral Resources David S. Potter SonTek/YSI Dr. John C. Wiltshire †Athelstan Spilhaus South Korea University of Hawaii †E. C. Stephan Dr. Seok Won Hong Marine Security †Allyn C. Vine Maritime & Ocean Engineering Research Inst. Dallas Meggitt †James H. Wakelin, Jr. (MOERI/KORDI) Sound & Sea Technology †deceased Washington, D.C. Ocean Economic Potential Capt. Dennis “Mike” Egan, P.E. EESS LLC MTS Needs Your Assistance!
dŚŝƐLJĞĂƌƚŚĞDĂƌŝŶĞdĞĐŚŶŽůŽŐLJ^ŽĐŝĞƚLJŝƐĐĞůĞďƌĂƟŶŐ 50 years of excellence.
ŶĚũƵƐƚŽŶĞŽĨƚŚĞǁĂLJƐƚŚĞ^ŽĐŝĞƚLJŝƐĐĞůĞďƌĂƟŶŐŝƐƉƵďůŝƐŚŝŶŐĂ ĐŽīĞĞͲƚĂďůĞƚLJƉĞŬƚƌĂĐŝŶŐƚŚĞĂŵĂnjŝŶŐĂĚǀĂŶĐĞŵĞŶƚƐŝŶŵĂƌŝŶĞƚĞĐŚŶŽůŽŐLJ ŽǀĞƌƚŚĞƉĂƐƚϱϬLJĞĂƌƐ͘
/ƚŝƐ͕ŽĨĐŽƵƌƐĞ͕ŝŶĞǀŝƚĂďůĞƚŚĂƚDd^ŵĞŵďĞƌƐǁŝůůĨĞĂƚƵƌĞƉƌŽŵŝŶĞŶƚůLJ͘dŚĞďƌŽĂĚ ĚŝǀĞƌƐŝƚLJŽĨƚŚĞŝŶƚĞƌĞƐƚƐƌĞƉƌĞƐĞŶƚĞĚďLJŽƵƌWƌŽĨĞƐƐŝŽŶĂůŽŵŵŝƩĞĞƐĂŶĚŽƵƌ ĐŽŶĨĞƌĞŶĐĞƉƌŽŐƌĂŵƐƐƉĂŶĂůůŽĨƚŚĞŬĞLJĚŝƐĐŝƉůŝŶĞƐƚŚĂƚƉƌŽĚƵĐĞĚƚŚĞ ĂĚǀĂŶĐĞƐƚŚĂƚŚĂǀĞŚĞůƉĞĚƚŚĞǁŽƌůĚĚŽĂďĞƩĞƌũŽďŽĨĞdžƉůŽƌŝŶŐ͕ƉƌŽƚĞĐƟŶŐĂŶĚ ƵƟůŝnjŝŶŐƚŚĞƉƌĞĐŝŽƵƐŽĐĞĂŶƌĞƐŽƵƌĐĞƐƚŚĂƚĐŽǀĞƌϳϬƉĞƌĐĞŶƚŽĨƚŚĞ ĂƌƚŚ͛ƐƐƵƌĨĂĐĞ͘ Your assistance is needed!
te ǁeůcoŵe LJour contriďuƟons oĨ anecdotes͕ Ɖersonaů reŵeŵďrances͕ and Ɖictures͘
ŶĚǁĞůŽŽŬĨŽƌǁĂƌĚƚŽƐĞĞŝŶŐLJŽƵĂƚŽƵƌďŝŐĐĞůĞďƌĂƟŽŶĂƚK E^͛ϭϯDd^ͬ/ ^ĂŶŝĞŐŽŝŶ^ĞƉƚĞŵďĞƌ͊
WůĞĂƐĞƐĞŶĚLJŽƵƌŵĂƚĞƌŝĂůƐƚŽ DĂƌLJĞƚŚ>ŽƵƟŶƐŬLJĂƚŵďůŽƵƟŶƐŬLJΛŐŵĂŝů͘ĐŽŵ͘ ŽŶƚƌŝďƵƚŽƌƐǁŝůůďĞůŝƐƚĞĚŝŶƚŚĞŬ͕ĂŶĚĂůůƉŚŽƚŽƐĂŶĚŵĂƚĞƌŝĂůƐǁŝůůďĞ ĂĐŬŶŽǁůĞĚŐĞĚĂŶĚƌĞƚƵƌŶĞĚ͘ The Marine Technology Society is COPYRIGHT Editorial Board a not-for-profit, international professional Copyright © 2013 by the Marine Technology Ann E. Jochens, Ph.D. society. Established in 1963, the Society’s Society, Inc. Authorization to photocopy Editor mission is to promote the exchange of items for internal or personal use, or the Texas A&M University information in ocean and marine engineer- internal or personal use of specific clients, is granted by the Marine Technology Society, Brian Bingham, Ph.D. ing, technology, science, and policy. provided that the base fee of $1.00 per copy, University of Hawaii at Manoa plus .20 per page is paid directly to Copyright Please send all correspondence to: Donna Kocak Clearance Center, 222 Rosewood Dr., The Marine Technology Society HARRIS Corporation Danvers, MA 01923. 1100 H Street NW, Suite LL-100 Scott Kraus, Ph.D. Washington, DC 20005 For those organizations that have been New England Aquarium (202) 717-8705 Tel. granted a photocopy license by CCC, a sepa- Dhugal Lindsay, Ph.D. (202) 347-4305 Fax rate sys tem of payment has been arranged. Japan Agency for Marine-Earth Science MTS Journal: [email protected] The fee code for users of the Transactional & Technology Publications: [email protected] Reporting Service is 0025-3324/89 $1.00 + Membership: [email protected] .20. Papers by U.S Government employees Justin Manley are declared works of the U.S. Government Teledyne Benthos Programs: [email protected] Director: [email protected] and are therefore in the public domain. Eugene Massion Online: www.mtsociety.org The Marine Technology Society cannot be Monterey Bay Aquarium Research Institute held responsible for the opinions given and Jill Zande MEMBERSHIP INFORMATION the statements made in any of the articles MATE Center may be obtained by contacting the Marine published. Technology Society. Benefits include: ■ Free subscription to the online Marine Editorial Technology Society Journal, with highly ABSTRACTS Donna Kocak reduced rates for the paper version VP of Publications MTS Journal article abstracts, if available, ■ Free subscription to the bimonthly news - can be accessed for free at http://www. Ann E. Jochens, Ph.D. letter, Currents, covering events, business ingentaconnect.com/content/mts/mtsj. Editor news, science and technology, and Amy Morgante people in marine technology Print and electronic abstracts of MTS Journal Managing Editor ■ Member discounts on all MTS publications articles are also available through GeoRef
4 Marine Technology Society Journal INTRODUCTION DeepStar®: 22 Years of Success DeepStar: A Global Deepwater Technology Development Program
AUTHORS its organization, operation, and direc- With DeepStar membership includ- Greg Kusinski tion. Some additional detail is provided ing over 80 organizations employing Chevron Energy Technology on historical major accomplishments well over 1 million people and operat- Company and as well as current research activities ing in all of the world’s deepwater and DeepStar Director and a vision of the future for deepwater ultradeepwater basins, it is well posi- success. tioned to ensure members are focused Art J. Schroeder, Jr. on the right technical challenges and Energy Valley, Inc., and leveraged to produce meaningful and DeepStar Consultant DeepStar Overview value-added results. See Figure 2 for a James E. Chitwood DeepStar is an operator-driven and listing of current members. Chitwood Engineering and funded research and development DeepStar has a proven and long- DeepStar Consultant (R&D) collaboration between oil term record for delivery of value to companies, vendors, regulators, and its membership. Its mission is to facil- academic/research institutes started in itate a cooperative, globally aligned fi Introduction 1991. Within the overlap of operator effort focused on identi cation and he oil and gas industry has long member-driven, collaborative space development of economically viable established a collaborative approach deepwater technology needs, DeepStar methods to drill, produce, and trans- T port hydrocarbons from deepwater. to reduce risks and optimize results, serves as a well-proven tool to lever- especially in the area of technology age resources of a multitude of scarce DeepStar’s current Phase XI program development for major exploration sources. Leverage includes is focused on global deepwater develop- and production (E&P) projects. In ■ direct hard-dollar funding of third- ment in water depths to 10,000+ feet. 1991, a visionary group of industry party R&D suppliers; As the premier global forum to de- operators laid the foundation for ■ DeepStar member internal techni- fine deepwater technology needs, it what is DeepStar® today, a highly cal expertise, subject matter experts provides value to its membership by successful initiative for technical col- (SMEs) from both Participants (op- leveraging financial and technical re- laboration to enhance deepwater ex- erators) and Contributors (manufac- sources to ploration, drilling and production. tures, service companies, universities, ■ define and rank important deep- The Chevron-managed, consensus- engineering firms, etc.); water technology needs, driven DeepStar consortium has ■ in-kind contributions including pre- ■ delivertechnologiesviaawellhoned evolved steadily during the past two vious work in the field of interest; stage-gate process, decades to meet ever increasing tech- ■ potential field test/demonstration ■ build deepwater technical nical challenges of deepwater devel- opportunities; competency, opment and production. However, ■ a well-honed, effective and efficient ■ adopt and deploy deepwater it has never wavered from its core set of processes and procedures; technologies. mission to provide our industry with ■ a respected track record of success in- DeepStar has established goals to an open platform to investigate terfacing with regulatory agencies and ■ enhance existing deepwater tech- complex technical challenges and standards-developing organizations. nologies by improving the safety, collaboratively develop safe, viable Figure 1 outlines the role DeepStar operability, flexibility, reliability, solutions. This article outlines occupies to meet operator members’ and profitability of existing deep- DeepStar’s strategies and overviews collaborative technology needs. water production systems;
May/June 2013 Volume 47 Number 3 5 FIGURE 1
Collaborative space deepwater R&D needs.
Operator Members (Participants) have desire for collaborative funding where facilities & deepwater technologies will not provide a competitive advantage (This was the original driver that started DeepStar.)
■ DeepStar is a proven well leveraged tool in a collaborative space
■ DeepStar is an Operator-Driven Program (e30 Multi-Discipline Projects).
■ DeepStar is a recognized Industry collaborative voice.
■ There is an opportunity for members to benefitfrom DeepStar by participating in fewer – but larger and “better” JIPs
FIGURE 2
DeepStar is a consortium membership; Phase XI (as of 4/23/2013).
6 Marine Technology Society Journal ■ develop new enabling deepwater cause a ripple affect across the entire tees are currently charged as outlined technologies by advancing novel industry. As such, DeepStar provides an below. technologies to allow production outstanding opportunity for SMEs to col- Geosciences Committee (×000) in areas that are currently techni- laborate and foster the exchange of ideas. addresses challenges in prospect cally unproven with the ultimate and reservoir delineation, character- goal of developing technologies re- ization and surveillance, which are quired for economic production in DeepStar Organization either specific to deepwater prov- 12,000+ feet water depth; DeepStar is managed by Chevron inces or which relate to appraisal and ■ gain acceptance of deepwater via a contractual arrangement with its development decisions leading to technologies by regulators and participating organizations, utilizing significant economic impact in such industry by facilitating the devel- Chevron back-office support services provinces. opment of industry standards and including legal, procurement, financ- Regulatory Committee (×100) practices as appropriate and foster- ing, accounting, and administrative. provides liaison between DeepStar ing communications with regula- Chevron also provides a Director and technical committees and governmen- tory agencies; a technical staff of two industry vet- tal regulators such as the Bureau of ■ provide a forum and process for erans to support the consortium. Safety and Environmental Enforce- discussion, guidance and feed- DeepStar, with 11 deepwater operat- ment (BSEE) and the U.S. Coast Guard. back with contractors, vendors, op- ing companies and approximately 80 The objective of the committee centers erators, regulators and academia, contributing member companies, is on the exchange of technical informa- regarding deepwater technology, the world’s longest running deepwater tion between the working technical and promote standardization of consortium. One thousand plus tech- groups in DeepStar and regulatory rep- component interfaces. nical and management committee vol- resentatives. The Regulatory Commit- Thesegoalsareaccomplishedvia unteers coupled with straightforward, tee also works and communicates with the following DeepStar execution well-honed and proven policies and pro- leading industry organizations, such as strategies: cedures also make it one of the most the Offshore Operators Committee ■ technology development aligned successful. The SMEs are organized (OOC), American Petroleum Institute with business needs; functionally into Technical Committees (API), and others. The objective of ■ transfer and apply technology to with operator chairs (and co-chairs) as this interface between DeepStar and deepwater assets; shown in Figure 3. other parties is the expedient full re- ■ gain acceptance of deepwater tech- The Technical Committees’ role view of relevant issues involved in de- nologies by industry, standards orga- is to identify technology needs and ployment of new tools or processes nizations, and regulators; then generate “ideas”—captured on under development. ■ focus on the front end of the technol- a cost, time, and resources (CTRs) Flow Assurance Committee ogy development cycle by advancing form for Management Committee re- (×200) goal is to assure reliable and critical fundamental knowledge view. Once approved and bid out, economic production in deepwater (science), providing proof of concepts their role is to review and recommend by appropriate design and operation and performing techno-economic awards to the DeepStar Director. through prediction of fluid behavior, engineering studies. Once awarded, their role is to oversee flow management, and remediation While the manufacturing and service and technically guide the execution of of deposition and line plugs from the sector members compete fiercely, most the work. The Technical Committees reservoir to the point of sale. DeepStar work is considered a “non- also table discussions/presentations of Subsea Systems Committee competitive” area between the operators new technologies and/or challenges (×300) goal is to develop technology and thus a suitable space for collabora- that could potentially be addressed and qualify equipment to enable the tion.Thisalsoincludesprojectsthatsup- within the DeepStar program. Time deployment and IMR of “subsea facil- port reliable and safe operations. From spent by the various Committee mem- ities for 50+ mile tie-backs in 10,000 an operator perspective, there is high bers on Technical Committee activi- foot water depth.” value in collaborating on these topics, ties is contributed by their respective Floating Systems Committee as an incident with one operator can companies. The Technical Commit- (×400) role is to further technology
May/June 2013 Volume 47 Number 3 7 FIGURE 3
DeepStar organization.
and fill gaps related to deepwater float- ing global characteristics of deepwater Operational Framework ing systems and their associated moor- reservoirs. The DeepStar R&D projects are ings and risers. Met-Ocean Committee (×800) funded by operator fees, and the de Drilling, Completions, and In- goal is to improve knowledge and minimus cash fee from nonoperator tervention Committee (×500) mem- modeling capabilities of ocean cur- members helps offset meeting costs. bers share their experiences and data to rents, waves and wind, which will pro- While all member classes may propose identify technology improvements in vide more accurate facility design projects, the final funding decisions are deep water drilling, completion, and criteria and reduce downtime during taken by the operators, known within well intervention operations. deepwater drilling operations. DeepStar as Participants.Thismakes Administration and Technical Systems Engineering Committee sense not only by the fact they are the Support (×600) — The Program (×900) has the responsibility for ana- ones funding projects but they are also Director heads this committee and lyzing existing and/or potential tech- the “voice of the customer” for the man- oversees DeepStar’s leadership and ad- nology gaps, especially at the facility ufacturing, engineering, and service ministration responsibilities. systems level and bringing them to the company members, known as Contrib- Reservoir Engineering Commit- attention of the committee best suited utors. The entire project selection pro- tee (×700) looks at trends that are of to carry out further work in the specific cess provides the Contributors with a significant generic interest to the in- technology area. very clear understanding of their cus- dustry, while avoiding detailed reser- A huge benefittomembersisthe tomers’ needs and priorities in the col- voir issues where participants have interconnectivity and continuity the laborative space (Figure 5). competitive concerns. The committee staff bring by linking together the pieces All DeepStar projects must has assembled the best available public of the deepwater technology puzzle as have an operator Champion.Cham- domain information for use in learn- shown in Figure 4. pions, along with DeepStar staff, are
8 Marine Technology Society Journal FIGURE 4 ■ define costs, ■ implement CTR, DeepStar technical committees span the deepwater technology puzzle. ■ select contractors (bid process), ■ submit justification for manage- ment approval, ■ insure contract implementation, ■ arrange kickoff meeting, ■ arrange for progress meetings, ■ review monthly reports and provide periodic updates to the Technical Committee, ■ maintain consensus, ■ approve and confirm contractor invoices, ■ approve Final Report. While DeepStar projects can span the development spectrum, character- istics of a typical DeepStar project are as follows: FIGURE 5 ■ operator championed, ■ lower technology readiness level DeepStar project funding roadmap. (i.e., TRLs 1–3 on a scale of 1–7), ■ low cost (200 k–500 k USD), ■ shorter duration (6–18 months), and ■ multiphase stage-gated.
DeepStar Successes DeepStar has successfully identi- fied and executed hundreds of R&D projects over its 11 phases, which have subsequently enabled member compa- nies to achieve their business objectives. Some of the successes have been in the following technical arenas: ■ Poly rope: development, recom- mended practices, standards and regulatory approval; ■ FPSOs: standards and regulatory approval; ■ Vortex-Induced Vibration: under- standing, prediction, mitigation responsible for the execution of their project and providing peer guidance. and control; projects and are held accountable for With DeepStar staff assistance, Cham- ■ Met-Ocean: understanding, pre- the deliverables (results, schedule, and pions and their Working Committees diction and design practices and cost). A subcommittee, or Working fulfill the following roles for each ap- standards; Committee, is usually formed to sup- proved CTR: ■ Promulgator of standards and port the Champion in executing the ■ refine scope of work, regulations;
May/June 2013 Volume 47 Number 3 9 ■ Flow assurance management, in- FIGURE 7 cluding modeling, operations, DeepStar modeling and simulation tools. remediation. As DeepStar members (not Deep- Star itself ) sell kit and services, the nonmember may have difficulty in immediately seeing the underlying DeepStar value-add. Outlined in Fig- ure 6 are some of the standards and ■ Life Cycle Well Cost Control Evaluation Tool Commercial recommended practices emanating ■ Well Control Software Commercial from DeepStar work in the equip- ■ Reservoir Characterization and Performance Database Commercial ment area. ■ GOM Current & MetOcean Forecast Models Commercial Examples of areas where DeepStar ■ Hydrate Plugging in Oil Model Commercial work in the modeling and simulation ■ Hydrate Disassociation Model Benchmarking arena has given rise to commercial ■ Asphaltene Deposition Model and Lab Test Benchmarking solutions are presented in Figure 7. ■ Annulus Pressure Buildup for XHPHT Wells Commercial Continually being at the forefront of deepwater developments, Deep- to governmental agency rules and reg- agement Committee. Current phase Star, in its various studies, has set the ulations, some of which are listed projects can be grouped as shown in groundwork on many of the safety in Figure 8. Figures 9 and 10. standards we know today. In particu- lar, DeepStar drove the development of the Technology Qualification Pro- Current Phase XI DeepStar, the Future cess (TQP), which much of indus- Focus Areas While Neils Bohr is quoted as try leverages for their R&D efforts to The DeepStar process utilizes an saying, “Prediction is very difficult, accurately represent the maturity of operator-driven CTR tool to help iden- especially if it’s about the future,” new technology. Additionally, much tify projects of interest. The CTRs are it is clear that DeepStar’sfutureis of the DeepStar work that led to vari- operator vetted and ranked at the bright as it will continue to evolve ous standards and recommended Technical Committee level and then and remain relevant, following a practices has since been promulgated prioritized by the Senior Advisor Man- strategy finely honed over the past 20 years. First, there is no shortage of “needs” for new technologies in the FIGURE 6 collaborative space. Post-Macondo, DeepStar equipment programs. the industry is placing even more emphasis on building and maintain- ing sustainable Integrity Management programs with particular focus on in- clusion addressing low probability, high consequence events. Additional efforts are also expected in the devel- ■ ROV Interfaces InAPI 17H opment of standards and protocols ■ Subsea Equipment Qualification API 17N leading to greater reliability, better/ ■ HIPPs for the GOM InAPI 17O more effective interfaces between in- ■ Qualification of Large Bore HP Valves Updated API 17D dividual components and equipment ■ DW Pipeline Repair & Tie-Ins DW RUPE modules, and more effective mainte- ■ Pipeline Limit State Design Codes API RP 1111 nance procedures and practices, all ■ Subsea Multiphase Flow Meters API RP 85 adding up to a safer overall operating ■ Drilling Riser Recommended PracticeUpdated API 16Q environment. These strategies should
10 Marine Technology Society Journal FIGURE 8 CTR “bottoms up” need-driven pro- cess with strategic overarching top- DeepStar safety programs. down direction. The needs will be both near term (to 5 years) and longer term (to 10 years). As such, DeepStar will continue to fund “individual proj- ects” within all the Technical Com- Safety is the guiding tenet during the design, deployment and operations mittees that are operator driven and phase of all DeepStar projects anticipates adopting a few overarch- ing areas of focus with an emphasis on ■ DeepStar draft Deepwater Operating Plans BSEE DWOP Standards where appropriate. Near ■ Safe Hydrate Remediation Guideline & Operations DeepStar Guideline term one could also expect projects sup- ■ Real-Time SS Monitoring & Modeling for SS Control Commercial porting better appraisal tools, Increased ■ Subsea Prod. System Reliability & Risk Mgmt API 17 N Oil Recovery (IOR), particularly in the ■ Deepwater Pipeline Limit State Design in Codes API RP 1111 Lower Wilcox, Subsea processing and ■ Technology Qualification Process Standardization API 17N Drilling, Completion and Intervention ■ Floating System Integrity Management Technologies DeepStar Guideline projects focused on supporting safer ■ Shallow Water Flow Management Best Practices Standard Practice operations with a lower overall cost. The Management Committee “ ” FIGURE 9 will be encouraging Bigger Impact projects that are conducted in a more DeepStar Phase XI project types (only third-party direct spend included in budget numbers; in collaborative manner, particularly with addition are the value of Participants and Contributors SME time and in-kind contributions). larger Contributors. To better facilitate this outcome, there will be some sensi- ble changes to the standard DeepStar Intellectual Property restrictions based on overall balance of value delivered to project. DeepStar traditionally provides the collective “Voice of the Customer” to member service and manufacturing companies, allowing them to provide better focused, more reliable services and products at a lower cost. Leveraging on this role, DeepStar is asking members to consider DeepStar as an alternative of choice versus spinning-up new or par- ticipating in other “one-off” Joint In- dustry Projects (JIPs). DeepStar expects to continue interaction with regulators to ensure DeepStar-developed technologies can also yield an overall lower total cost those collaborative areas most highly be readily accepted for deployment of ownership. ranked by the operators. Its “holistic” and use. The strategy will continue DeepStar’s current Management approach with eight Technical Com- presenting a well-defined operational and Technology Committee structure mittees provides a synergy that is need and DeepStar’sstage-gatetech- will continue as is and its time-honed greater than just the sum of the indi- nology development solution to regula- processes have served its membership vidual committees. Generally, Deep- tors at an early enough point so as to be well, directing funds and resources to Star will continue with the successful able to incorporate appropriate action
May/June 2013 Volume 47 Number 3 11 FIGURE 10 Acknowledgments The authors gratefully acknowl- The current suite of projects and how they support DeepStar’s current high-level field develop- ment scenarios. edge the contributions of the DeepStar member organizations for their input and support.
plans to address any regulatory concern ● $100 MM of projects and 325+ without incurring development delays. technical reports, ● 1,000+ Subject Matter Experts, ● 70+ member organizations pro- Conclusions and Summary vide ample opportunities for The world’s deepwater and ultra- field test and demo; deepwater basins hold tremendous ■ standardized, efficient and cost- resource promise to help meet global effective processes and procedures energy needs. DeepStar and its 80-plus ● procurement and contracting, member organizations have processes, ● portfolio vetting and selection, procedures and most importantly a ● project management, thousand-plus SMEs to help ensure ● technology transfer; that the most appropriate technologies ■ freedom to fund when and how are identified and then pursued and best to meet operators’ strategic pulled through to commercialization. needs in a timely manner, no pub- DeepStar successes are numerous and lic disclosure, go at right speed, have had long-term impact due in large start-stop-change direction for part to the operator lead and operator optimum results. Refocused every “pull” on project selection. Additional con- 2 years. tributing factors include the following: Organizations, including opera- ■ successful in defining and commu- tors, manufacturers, service compa- nicating gaps and needs, especially nies, as well as universities interested in the early TRL stages; in defining needs and developing ■ R&D directly relate to operator’s new technologies to safely and prof- future Major Capital Projects itably unlock the ultra-deepwater po- (MCP) developments; tential are invited to apply to join the ■ long-term stability, proficiency, DeepStar team. The reader of this and consistency of staff paper is encouraged to connect with ● 20 years identifying and leading DeepStar staff about participation deepwater technology develop- details. For more information, please ment and application, visit www.DeepStar.com.
12 Marine Technology Society Journal PAPER DeepStar 11304: Laying the Groundwork for AUV Standards for Deepwater Fields
AUTHORS ABSTRACT John Jacobson Emerging autonomous underwater vehicles (AUVs) developments across the Lockheed Martin Corporation oil and gas industry now include pipeline inspection; structural survey; deepwater Pierce Cohen inspection, repair and maintenance (IRM); and field resident systems for remote/ Chevron Energy Technology harsh environments. As these capabilities mature, AUVs will become an increasingly Company and DeepStar important tool for deepwater field operations. Early adoption of AUV standards will Project Champion facilitate more rapid deployment of AUV technologies and enable the industry to reap a wide range of safety, environmental, operational, and economic benefits Amin Nasr for its deepwater fields. The development of industry standards for AUV interfaces Total SA and DeepStar will facilitate more rapid implementation of AUV capabilities and lead to more cost- Project Champion effective, compatible system designs by AUV vendors and field hardware manufac- Art J. Schroeder, Jr. turers. The development of regulatory standards for the interpretation and acceptance Energy Valley, Inc., and of autonomous inspection results is also an essential step toward the achievement DeepStar Consultant of more cost-effective operations and regulatory oversight of deepwater subsea fields. This paper describes a future vision for the use of AUVs in deepwater field operations, Greg Kusinski the benefits to be realized, and the future capabilities of AUVs that must be anticipated Chevron Energy Technology and facilitated within AUV standards to achieve that vision. Additionally, this paper Company and DeepStar Director describes the goals and objectives of DeepStar Project 11304, which is laying the groundwork to achieve accelerated standardization of AUV interfaces and the devel- Introduction opment of regulatory standards for AUV inspections. fi ntil recently, autonomous under- Keywords: autonomous underwater vehicle (AUV), deepwater eld, interface standards, waterU vehicles (AUVs) in offshore regulatory standards, inspection oil and gas were limited primarily to bathymetric/geophysical survey, but emerging developments across the sub- deepwater field operations. Early adop- positioning (DP) II vessels and thou- sea industry now open the potential for tion of AUV standards will facilitate sands of square feet of deck space for safer, better, and cheaper pipeline in- more rapid deployment of AUV tech- support equipment that can weigh spection; structural survey; deepwater nologies and enable the industry to reap up to 90 tons. Vessel operations are inspection, repair and maintenance a wide range of safety, environmental, limited by weather, mobilization/ (IRM); and field resident systems for operational and economic benefits for demobilization timelines, and opera- remote/harsh environments. Industry not only deepwater fields but poten- tional constraints, which can be due developments range from low-logistics tially for all offshore developments. to umbilical deployment in deepwater. AUVs that simply “mow the lawn,” to Extended vessel deployments at high semiautonomous “delivery trucks” with day rates are required to complete remotely operated payloads, to AUVs Future Vision for AUVs ROV-based IRM operations due to with highly integrated perception re- in Deepwater Fields these inefficiencies, driving the costs sponse autonomy that provides sig- The performance of IRM tasks of field operations and maintenance nificant ability to interpret sensor data in deepwater using current methods in deepwater to millions of dollars and respond accordingly. As these ca- with remotely operated vehicles (ROVs) per year. Under these circumstances, pabilities mature, AUVs will become can be costly and inefficient. Deep- the development of smaller “marginal an increasingly important tool for water ROVs require large dynamically fields” or deepwater fields in remote
May/June 2013 Volume 47 Number 3 13 locations or hostile environments such routine maintenance tasks. The value high maneuverability and full hovering as under arctic ice may drive a prospect of these capabilities for remote deep- capability, which will be used to con- to low or noncommercial viability. water and/or arctic locations cannot duct inspection of subsea infrastruc- The implementation of AUV-based be overstated, since it provides imme- ture such as wellheads, manifolds, IRM will provide significant improve- diate in-field access to complete tasks jumpers, spool pieces, flowlines, and ments in safety, operating efficiency, that would otherwise take days or risers. Sensors include still and HD and project economics for deepwater weeks to accomplish, especially consid- video camera, lighting, 3D imaging fields. No longer will large DPII vessels ering the mob-demob time associated sonar, and profiling sonar. The AIV is with expensive and cumbersome ROV with ROVs. deployed by an “intelligent basket” that spreads be required for simple IRM. In is lowered to the seabed and enables the near term, AUVs can be deployed autonomous IRM operations without from smaller “utility class” vessels, be Current AUV Development surface vessel support over a period capable of operations in higher sea Trends for Deepwater of days until retrieved (Jamieson et al., state and current conditions, and per- There are a number of ongoing 2012) (Figure 1). form IRM tasks much more efficiently AUV developments for deepwater oil The Sabertooth AUV, under devel- without the operational limitations and gas that, when brought to full com- opment by Saab SeaEye, is targeted and equipment hazards imposed by mercial capability, will have game- for autonomous, field resident, sub- umbilical and tether management sys- changing implications for deepwater sea facilities inspection. Designed for tems. Reduction in equipment com- field operations and maintenance. remote inspection and intervention plexity, vessel size, and crew size will These include pipeline inspection, tasks without the need for a support also result in improved safety, reliabil- deepwater facilities inspection, and ship, the Sabertooth will be capable ity, and lower environmental impact. field resident AUV capabilities. of long distance transits between Eventually, AUVs will become “field With its HUGIN AUV, Kongsberg work sites and of docking with a subsea resident,” residing in the subsea field Maritime has demonstrated autono- docking station that is deployed within for periods of months or years, resulting mous multisensor pipeline inspection, the subsea field. The docking station in the elimination of surface vessels, fur- including collection of detailed digital will provide interfaces for battery ther improvements in environmen- still imagery of an underwater pipeline charging, high bandwidth data trans- tal monitoring, equipment safety, and by using interferometric synthetic ap- fer, and mission planning and control. operating efficiencies, and substantial erture sonar (SAS), pipeline tracking Targeted to remain submerged for up reductions in cost. software, a multibeam echo sounder, to 12 months, the system will also be Future capabilities for deepwater and a high-resolution still camera in capable of tethered operations using a AUVs will be substantially enhanced a two-pass mission. In the first pass, microfiber tether. The system can de- through the use of subsea docking sta- side-scan data from the SAS are used ploy a range of sensors and tooling for tions and local Wi-Fi “hot spots.” The to detect and track the pipelines in inspection and intervention on subsea ability to upload high volumes of mis- real time, extracting pipeline features production systems (Furuholmen et al., sion sensor data, download supervisory in the sonar images. In the second 2010) (Figure 2). instructions, and recharge batteries pass, the AUV conducts a low-altitude will extend AUV mission life to days inspection of the pipeline using its or weeks and eventually to months multibeam sonar and optical camera. FIGURE 1 and/or years. The ability to have local- Imagery is postprocessed into high- SubSea 7’s AIV. ized real-time high bandwidth wire- resolution sonar images and bathyme- less communications for critical IRM try maps of the pipeline (Borhaug & operations such as subsea production Hagen, 2011). equipment monitoring, sampling, The autonomous inspection vehi- valve operations, and other interven- cle (AIV), currently under development tion operations will eliminate the need by Subsea 7, is targeted for subsea fa- to mobilize expensive surface vessels cilities inspection. The AIV employs and large ROV spreads to accomplish a compact, ROV-like shape to achieve
14 Marine Technology Society Journal FIGURE 2 FIGURE 3 high bandwidth communications and data transfer, and mechanical Sabertooth AUV from Saab SeaEye. Lockheed Martin’s Marlin® AUV. interfaces for docking, tool storage, and interchange. Docking stations mayalsofacilitatetheuseoftether management systems for semiauto- nomous vehicle systems. Other per- manently installed interfaces that would leverage the benefits of AUV capabilities include wireless subsea communication nodes (radio frequency (RF), acoustic, optical, and/or hybrid), data harvesting nodes, subsea produc- The SWIMMER system, under shore production platforms, downed tion equipment monitoring and sam- development by Total and Cybernetix, structures, and debris fields in a mat- pling points, and intervention tooling employs a hybrid AUV-ROV approach ter of minutes or hours, with typical interfaces. to achieve vessel-independent, field res- model resolution of ∼5 cm. The ca- The development of industry stan- ident IRM operations in remote and/or pability to perform 3D laser inspec- dards for AUV interfaces, similar to deepwater environments. The system tions yielding 3D models with ∼5mm the API/ISO standards for ROVs, features a large AUV that is launched resolution is under development. Also will lead to compatible system designs from a support vessel, transits many under development is a 4,000-m by AUV vendors and field hardware kilometers to a docking station within depth-rated version of Marlin with manufacturers and will enable more a subsea field, and docks to one of many full station keeping capability, which cost effective development and more dedicated docking stations staged will be used to facilitate inspection efficient operations of deepwater sub- within the field. Once docked, a work- of subsea infrastructure. This version sea fields. As sensor and AUV manu- class ROV is deployed from the AUV of Marlin will be capable of being facturers design and operators deploy to perform a wide range of IRM tasks launched from a floating production compatible kit, the expense (capex using typical ROV tooling and sensors. system (FPS), conducting flowline and and opex) versus the value of subsea The ROV can work within a 150-m riser inspections during transits of 15– data collected will drop by orders of watch circle from the docking station; 20 km, followed by inspection of in- magnitude in a positive re-enforcing work beyond that radius requires the field infrastructure such as wellheads, cycle. The offshore oil and gas industry AUV to transit to a new docking sta- manifolds, jumpers, and spool pieces, has the benefit of many lessons learned tion to perform the work. The system and then returning to the FPS for recov- from the development of ROV inter- is targeted for periods of up to 90 days ery and mission data retrieval (McLeod faces over a period of approximately submergence before being retrieved et al., 2012) (Figure 3). 20 years of development from the for maintenance (Tito & Rambaldi, early 1970s to the early 1990s. During 2009). the early days of ROVs, each field de- The Marlin® AUV, developed by AUV Interface Standards velopment project developed its own Lockheed Martin, is designed to pro- for Deepwater Fields unique installation, operations, and vide a wide range of structural integrity Future capabilities for deepwater maintenance procedures, which typi- management capabilities, including AUVs will be substantially enhanced cally resulted in unique interfaces for structural survey, subsea facilities in- through the use of permanently in- intervention tooling. As a result, pro- spection, and pipeline inspection. Fea- stalled field infrastructure such as jects frequently paid a high price for turing a hydrodynamic hull form with docking stations, communications “reinventing the wheel,” including hovering capability, an interchange- nodes, and other interfaces. Docking the cost of nonrecurring engineering able, under-slung work package (pylon), stations will provide electrical and/or design, the cost to procure unique the Marlin employs a 3D sonar to de- inductive interfaces for battery charg- tooling (and the inability to reuse the velop geo-registered 3D models of off- ing, optical or wireless interfaces for tools on subsequent projects), and
May/June 2013 Volume 47 Number 3 15 the inability to invoke full competition the regulation specifically recognizes DeepStar Project 11304: for offshore services due to being tied the inspection method (diver or ROV Laying the Groundwork ’ “ to a single vendor stechnology.Asa inspection) where a human is in the for AUV Standards result, the costs of operations, mainte- loop.” DeepStar is a joint industry tech- nance, and spares frequently grew over Additionally, as sensor and auton- nology development project focused time due to the difficulty and complex- omy technologies advance, the de- on advancing the technologies to ity of maintaining unique tools and ployment of autonomous inspection meet its members’ deepwater business fi procedures for each subsea eld. Fur- technologies will provide a range of needs to deliver increased production ther adding to cost and potentially new and as yet unrecognized formats and reserves. It provides a forum to compromising safety, the lack of stan- for inspection results, which when as- execute deepwater technology devel- dards drove the need for customized sessed using state of the art engineering opment projects and leverage the operator training for each installation tools, have the potential to provide con- financial and technical resources of and tended to complicate rotational siderable improvements in inspection the offshore oil and gas industry. fi and/or multiclient deployments. effectiveness as well as ef ciency and DeepStar’s membership is composed Through early standardization, the in- cost. For example, the use of 3D model- of companies and organizations from dustry can leverage these lessons to ing and autonomous change detection across the industry and the globe, reap the rewards with sensible, well- using 3D sonar, while not currently including oil companies, vendors, reg- thought standardization for AUVs. recognized by any regulatory standard, ulators, and academic and research would dramatically improve the ability institutions. DeepStar runs in 2-year to quickly and effectively identify fea- funding phases, and participation is Regulatory Standards for tures that have changed since a previ- by phase. In Phase XI, membership AUV Inspections ous structural survey. The capability includes 11 major oil companies and In the future, AUVs will leverage to identify, map, and measure features over 70 contributing companies from a wide range of sensor technologies such as free span, seabed scour, bent, industry and academia. to meet both end user and regulatory missing or damaged structural mem- DeepStar has funded Project 11304, requirements for integrity monitoring bers, and/or distorted or twisted beams AUV Standards for Deepwater Fields, of offshore infrastructure. Offshore in- would provide a significant advantage and through this project is laying the frastructure that falls under regulatory in posthurricane inspection operations. groundwork to achieve accelerated oversight includes fixed platforms, float- Similarly, performing autonomous standardization of AUV interfaces and ing structures, pipelines, risers, mooring structural inspection using a 3D laser the development of regulatory stan- lines and subsea production equipment. would provide the capability to quickly dards for AUV inspections. The project Sensor technologies that can be em- and efficiently identify, map, and mea- comprises two major tasks: ployed by AUVs to meet inspection sure cracks and other structural defects Task 1 – AUV Interface Standards requirements include video, photo- or damage. Utilizing these advanced for Deepwater Fields, and graphic, sonar, laser, ultrasonic, mag- technologies and techniques will help Task 2 – Regulatory Standards for netic, and others. minimize the need for divers, par- AUV Inspections. Today, most regulations and in- ticularly in the initial incident triage The primary goals of this project dustry standards do not address the phase where the risk of the unknown are as follows: use of AUVs for inspection, primarily is highest. (1) identify subsea interfaces that because the technology did not exist at The development of regulatory should be standardized for AUVs, the time the regulations were devel- standards for the interpretation and develop recommendations for ap- oped. While AUVs can be used to acceptance of autonomous inspection propriate standards related to sub- meet standards where only the sensor results where no diver or ROV pilot sea interfaces for AUVs, and begin technology is specified (e.g., “sonar is involved is therefore an essential the process of approval/release with frequency of at least 500 kHz”), step toward achievement of a safer, through an appropriate standards the regulations are frequently either more cost-effective and efficient opera- organization; and ambiguous or prohibitive regarding tions and maintenance of deepwater (2) identify current regulatory in- the use of AUVs. In other instances, subsea fields. spections that could be conducted
16 Marine Technology Society Journal with AUVs, develop draft versions FIGURE 4 of appropriate standards for such DeepStar 11304 Project Road Map. AUV inspections of subsea infra- structure, and make available work products that could help facilitate regulatory agency review and po- tential adaptation. In order to keep the scope of the project manageable, a single entity was selected for each Task as the primary stakeholder with whom to hold discus- sions and to whom to submit recom- mendations on AUV standards. For Task 1, the American Petroleum Insti- tute (API) Subcommittee 17 (SC17) was identified as the most appropriate standards organization for the develop- ment of AUV interface standards. For Task 2, the U.S. Bureau of Safety and and future AUV Interface implemen- ment of recommendations within the Environmental Enforcement (BSEE) tations foreseen by the industry, (2) fa- DeepStar Project Team, presentation/ was identified as the regulatory agency cilitating discussion and interaction discussion of recommendations with having most appropriate jurisdiction amongst industry stakeholders regard- API SC17 and BSEE, and development regarding AUV inspections. ing AUV interface standardization, of formal work-products reflecting the In order to achieve the project ob- and (3) developing consensus within consensus opinion of the industry and jectives, a road map has been developed the industry on what AUV interfaces the applicable standards agency. to define top-level project activities and should be standardized and what those events leading to the development and recommended standards should include. submission of work-products to API The output of these activities will be Conclusion and to BSEE. An overview of the proj- shared with API SC17 in the form of The future vision for AUVs in deep- ect road map is provided in Figure 4. a Task Report, which could result in water fieldoperationsiscompelling. The project is currently in progress formal initiation of the development AUV technologies are evolving at very with an anticipated completion date of of API standards for AUV Interfaces. rapid pace, bringing new and powerful March 2014. The scope of Task 1 and The focus of Task 2 survey/ capabilities that offer significant safety, Task 2 efforts have been defined in de- workshop activities will be on (1) iden- environmental, operational and eco- tail, preliminary discussions with API tifying and documenting the current nomic benefits. In order to fully realize and BSEE are in progress, and industry and future AUV inspection technologies these benefits, future capabilities of surveys and workshops are planned for foreseen by the industry, (2) facilitat- AUVs must be anticipated and facil- spring 2013. Key industry stakeholders ing discussion and interaction amongst itated within industry standards and who will be engaged in the survey and industry stakeholders regarding current regulatory allowances. DeepStar Proj- workshop activities include Field regulatory standards that could be met ect 11304 is laying the groundwork Operators, EPC Contractors, Subsea using AUV inspection technologies, and to achieve standardization of AUV in- Hardware Providers, ROV/AUV Ser- (3) developing work products that will terfaces and regulatory allowance for vice Contractors, AUV Developers, be useful to BSEE, on which regulations AUVinspections.Bybringingindustry AUV Sensor Developers, and Interface couldbemostimprovedbyallowing stakeholders and standards agencies Technology Developers. inclusion of AUV inspections. together, early adoption of standards The focus of Task 1 survey/ After the survey and workshop can be achieved, thereby capturing the workshop activities will be on (1) iden- activities are completed, project fo- lessons learned with ROVs and ac- tifying and documenting the current cus will shift to review and refine- celerating implementation of these
May/June 2013 Volume 47 Number 3 17 game-changing AUV capabilities in ceedings, Offshore Technology Conference, deepwater fields. May, 2009. Houston, TX: Offshore Technol- ogy Conference. http://dx.doi.org/10.4043/ 19930-MS. Acknowledgments The authors gratefully acknowl- edge the contributions of the DeepStar member organizations for their input and support.
Corresponding Author: John Jacobson Lockheed Martin Corporation 10375 Richmond Avenue, Suite 400, Houston, TX 77042 Email: [email protected]
References Borhaug, E., & Hagen, P.E. 2011. AUVs Take On Pipeline Inspection. E&P Magazine Website. http://www.epmag.com/Production- Drilling/AUVs-On-Pipeline-Inspection_86704. (accessed March 6, 2013).
Furuholmen, M., Johansson, B., & Siesjö, J. 2010. Seaeye Sabertooth: A Hybrid AUV/ROV Offshore System. In: MTS/IEEE Oceans 2010 Proceedings, September, 2010. Seattle, WA: IEEE. http://dx.doi.org/10.1109/OCEANS. 2010.5663842.
Jamieson, J., Wilson, L., Arredondo, M., Evans, J., Hamilton, K., & Sotzing, C. 2012. Autonomous Inspection Vehicle: A New Dimension in Life of Field Operations. Offshore Technology Conference Proceedings, April–May, 2012. Houston, TX: Offshore Technology Conference. http://dx.doi.org/ 10.4043/23365-MS.
McLeod, D., Jacobson, J., & Tangirala, S. 2012. Autonomous Inspection of Subsea Facilities-Gulf of Mexico Trials. In: Proceedings, Offshore Technology Conference, April–May, 2012. Houston, TX: Offshore Technology Conference. http://dx.doi.org/10.4043/ 23512-MS.
Tito, N., & Rambaldi, E. 2009. SWIMMER: Innovative IMR AUV. In: OTC 2009 Pro-
18 Marine Technology Society Journal PAPER DeepStar Metocean Studies: 15 years of Discovery
AUTHORS ABSTRACT Cortis Cooper In 1998, DeepStar began the first of many successful studies that have resolved Chevron Energy Technology Co. important questions concerning meteorological and oceanographic (metocean) Tom Mitchell processes that can cause large loads or fatigue problems on deepwater facilities. Consultant, Georgetown, Texas In so doing, these studies have immeasurably enhanced the reliability and safety of deepwater structures and pushed the frontiers of ocean science that have tradition- George Forristall ally been the realm of academic research. The efforts have focused on three major Forristall Ocean Engineering, Inc. phenomena: the Loop Current, Topographic Rossby Waves (TRW), and storm James Stear winds. Much of the DeepStar effort has focused on improving numerical models Chevron Energy Technology Co. of the respective phenomena because they can provide long historical databases at any site—data that serve as the basis for operating and extreme criteria with rea- sonable statistical uncertainty. Studies of the Loop include the first measurements Introduction of the Loop inflow and turbulence and evaluation of existing numerical models. ’ lmost all aspects of offshore facil- Most of DeepStar s efforts on TRWs started in 2008, and in a 5-year period, it ities are affected by winds, waves, and has developed a validated numerical model and used it to build a 50-year hindcast A database. Efforts are underway to use those results to build a stochastic forecast currents, including operations and cap- ital costs. Indeed, in many deeper water model. Finally, DeepStar has analyzed a large set of wind measurements taken from locations, the choice of the basic facility the powerful recent hurricanes and found that recommended formulas for wind fi fi is heavily influenced by the meteoro- pro les and spectra have signi cant bias and will be corrected in future recom- logical and oceanographic (metocean) mended practices. conditions, second only to the reservoir Keywords: oceanography, meteorology, metocean, ocean currents, ocean waves, characteristics and water depth. ocean winds Many mysteries remain concerning metocean variables, especially deep water currents and hurricane-driven remains concerning winds and waves, Loop Current windsandwaves.Nowhereisthistruer in part because few measurements have The Loop Current is a strong per- than in the Gulf of Mexico, where strong been made in strong hurricanes. manent current that flows through the ocean currents can be generated by sev- As a result of these myriad uncer- Yucatan Straits, loops northward, and eral different processes that can vary tainties and the importance of meto- then exits through the Florida Straits dramatically in magnitude over space cean criteria on safety and reliability, where it is renamed as the Gulf Stream. scales of a few kilometers. Several of DeepStar IV began significant funding About once per year, the Loop moves these processes were first discovered of metocean studies in 1998 and has northward of 27°N, becomes unstable, only recently, and their quantification continued this investment since then. and forms a large eddy that breaks has been led by Joint Industry Projects Thefollowingsectionsoutlinethema- away and drifts to the west. The Loop (JIP) like DeepStar, rather than the jor studies in more detail. Each section (which will henceforth be taken to traditional university oceanographers. is focused on a particular phenome- mean the Loop proper and its asso- Hurricanes have also been an area of non, e.g., Topographic Rossby Waves ciated large anticyclonic eddies) can active industry research because they (TRWs), so it frequently will cover occasionally affect shelf waters but is dominate the loads on most produc- several studies. Each section describes typically found in water depths greater tion facilities in deep water. Despite the study goals, business drivers, and than 500 m. Radial speeds within the their importance, major uncertainty methods and summarizes the results. Loop can exceed 2 m/s and generate
May/June 2013 Volume 47 Number 3 19 the drag equivalent of a hurricane first careful measurement of the inflow FIGURE 1 wave on mooring lines or generate boundary condition for numerical The TOMI instrument that was used to mea- vortex-induced vibrations that can models of the Loop. Such models are sure turbulence. The ADCP transducers are lead to fatigue failure of risers. These an important tool for developing design mounted on the bottom mast (forward look- effects influence the design of drilling and operating conditions and, perhaps ing), at the base of the (orange) upper mast and production risers, mooring ten- most importantly, for forecasting. (port and starboard looking), and behind the sions on production and drilling rigs, After the Yucatan Straits measure- lower mast on the main body (downwards looking). connection/disconnection of drilling ments, DeepStar quickly turned to an- risers, and installation of pipelines, swering another key question about mooring lines, tendons and hulls. the Loop Current: How turbulent is Although no firm accounting has ever it? At the time, designers were worried been done, we estimate that the Loop about the ability of turbulence to ex- costs the industry on the order of cite higher modes in the tendons of $10 million/year in rig delays. Tension Leg Platforms (TLPs) and The Loop was not discovered until spars. Current speed fluctuations can the late 1960s, and the first current affect these structures both by direct measurements did not occur until the forcing and by reducing the effective- early 1980s. Given the importance of ness of VIV suppressing strakes. These northern edge of the Loop Eddy in cur- the Loop and its relatively recent dis- effects have often been seen in model rents of up to 1.7 m/s. Turbulence was covery, it is not surprising that there basins where the turbulence intensity detected with the shear probes, but were many important unknowns that is 10–20% of the mean velocity. Oce- mostly in the 130–150 m depth range needed to be resolved as the industry anic turbulence levels were thought to around the local salinity maxima. The moved into deeper water. be much lower, but there was essen- level of turbulence was weak, and it In 1998, DeepStar initiated its tially no field data to prove that as- was distributed intermittently in both first oceanographic project by measur- sumption. DeepStar filled the gap by space and time. The most energetic ing the incoming source of the Loop funding measurements in a Loop Cur- events of turbulence had eddy scales Current—in other words, the water rent eddy using a unique instrumenta- of at most 4 m and velocity scales of inflow through the Yucatan Strait. tion system. The results are described only 1 cm/s. The typical and average val- Oceanographers had long wanted to by Mitchell et al. (2007). ues were more than 10 times smaller. take these fundamental measurements Measurements were made within After taking some basic physical but had been frustrated by the cost and the eddy and across the strong frontal measurements in the Loop Current, the politics of deploying instruments in boundary that separates the eddy from DeepStar’snexteffortwastounder- the eastern half of the Straits controlled the surrounding waters. A towed vehicle, stand the accuracy of available models. by Cuba. Not to be deterred, DeepStar the TOMI (Towed Ocean Microstruc- While many models were available at contracted CICESE, an oceanographic ture Instrument), was equipped with a the time, none had been rigorously val- research institution in Mexico that special 300-kHz ADCP that had its four idated. To fill this gap, DeepStar initi- had a cooperative research agreement beams directed fore, port, starboard, and ated a study in 2004 to compare five with Cuban oceanographers. CICESE down. The along-beam velocities re- existing forecast models. The modelers deployed eight moorings across the solved structures with wavelengths of were asked to run a 1-year historical Yucatan Straits with 33 single-point 4–60 m. The vehicle also carried shear period for which DeepStar had a pro- current meters and eight acoustic probes for measuring velocity fluctuations prietary, detailed set of measurements Doppler current profilers (ADCPs). in the dissipation range (0.5–100 cycles never before seen by the modelers. In addition, they conducted four ship permeter)andotherenvironmental Models were spun up by assimilat- surveys across the Strait during the sensors for measuring temperature, ing publicly available measurements 18 months that the moorings were in salinity, depth, and vehicle orientation. such as satellite altimetry. On the place. Results were documented in The towed body is shown in Figure 1. first day of each month, the models Abascal et al. (2003). The major ben- Tows were conducted at 25-, 50-, were run for 4 weeks without any efit of the study was to provide the 100-, and 150-m depths around the data assimilation. Model performance
20 Marine Technology Society Journal was judged by comparing the fore- The overall conclusion of the Phase 1 that the AEF model could provide casted to the observed distance of the study was that the models were too forecasts with useful accuracy, but its nearest major Loop or eddy front to inaccurate in forecast mode to be of success depended on having access to seven sites scattered over much of the much value to Industry operations, detailed in situ measurements from deep Gulf east of 94°W. Model results butthatfurtherworkwasjustified drifting buoys or other similar sources. were compared to persistence (the given the substantial benefits that Such measurements cost upwards of major fronts were assumed to remain could be had from an accurate forecast. $50,000/mo. stationary) for the entire month. Fig- Towards the end of the first model ure 2 compares the RMS (root mean intercomparison study, a new model square) error accumulated for the appeared on the scene that was quite TRWs 12 runs at all seven sites. Only one different to the others tested in Phase 1. In the late 1990s, British Petro- of the models was found to beat persis- AEF’s model was a so-called “feature” leum (BP) measured currents reaching tence after about 12 days, but not by model, which utilized proprietary drift- about 1 m/s near the seafloor in about much. Perhaps most striking was the ing buoys as well as satellite imagery to 2,000 m of water along an underwater substantial error exhibited by all the spin-up the model. Given the promise feature known as the Sigsbee Escarp- models right from the start (0 week). of this new approach, DeepStar de- ment. While the currents were most This strongly suggests that the satellite cided to fund a Phase 2 study using intense near the bottom, they remained imagery used to spin up the models theAEFmodelandtheOeymodel, substantial for hundreds of meters was far from perfect, probably because winner of the Phase 1 study. Figure 3 above the seafloor, finally reaching am- it failed to resolve the meanders and compares the error from the two mod- bient conditions at about 1,000 m. The frontal lobes commonly found on the els with that of persistence. The AEF Bureau of Ocean Energy Management Loop and its eddies. While these fea- model consistently beat the Oey model (BOEM; formally known as Minerals tures may have relatively short length and overtook persistence at about Management Service) deployed three scales (order 50 km), they can signif- 1 week. Its forecast error stayed flat current meters nearby for 18 months icantly affect the error metrics. The until the end of the second week and and observed similarly large currents. fact that the models did poorly even then slowly climbed until it was Figure 4 shows the time series of these in a nowcast mode suggested they double the initial error after 4 weeks currents. Subsequent analysis of the may have had substantial errors even where it remained steady until nearly BOEM measurements by Hamilton in a hindcast mode. 7 weeks. Overall, the conclusion was and Lugo-Fernandez (2001) suggested that the currents were driven by FIGURE 2 Topographic Rossby waves (TRW), a 200-km-long wave with periods of Comparison of forecast error from five Loop models with persistence. 10–14 days. TRWs can generate current speeds at the bottom near the Escarpment that far exceed those generated by any other phenomena. Such currents dominate the metocean extreme and fatigue loads on pipelines and risers, especially flexible risers (steel catenary risers or SCRs). DeepStar began its study of TRWs in 2003 by taking measurements of the cross-Escarpment variation of the waves, a characteristic that had not been studied before. Eight current meters were placed near the seafloor across the Escarpment at 91°08′W,
May/June 2013 Volume 47 Number 3 21 FIGURE 3 overlap in time and were later ob- tained by DeepStar. The 1 year of mea- Comparison of forecast error from two Loop models with persistence. surements showed strong variation along the Escarpment and confirmed the strong cross-escarpment variation first observed in the 2003 DeepStar measurements. The second project, begun in 2008, focused on the development of a numerical model with the goal of eventually using it to develop opera- tional and design criteria. Without a model, the industry would have had to develop criteria based on measure- mentsofonlyafewTRWsatafew locations. The latter was especially as depicted in Figure 5. BOEM had a In 2008, DeepStar restarted its troubling, because the measurements through-column mooring, L4, deployed efforts on TRWs because of increased showed that TRW-generated currents just to the south of the DeepStar array. exploration activity along the Escarp- varied significantly over length scales Over the 1-year deployment, about a ment and reports from drilling rigs of a few kilometers. half-dozen TRWs were measured and that were adversely affected by strong Florida State University (FSU) was showed the strongest currents occurred bottom currents. That year, two pro- contracted to develop the model and near the base of the Escarpment at S2 jects were started. The first involved soon discovered that the numerical and S3. Only about 10 km north at S6 taking more current measurements, discretization in standard ocean cur- speeds dropped off rapidly to less than but this time with moorings spread rent models generated substantial nu- half those observed at S2. In contrast, along the Escarpment as well as across. merical errors when dealing with the the reduction on the down-dip side Figure 6 shows the four DeepStar sharp bathymetric gradients of the of the Escarpment was much smaller, moorings as well as other moorings Escarpment. A more advanced numer- e.g., L4 was about 30% less than S2. deployed by Chevron and Shell, which ical technique was implemented, and the model was then used to hindcast the BOEM and DeepStar measure- FIGURE 4 ments (Dukhovskoy et al., 2009). Time series of near-bottom current vectors measured near the Sigsbee Escarpment. The vectors Results were encouraging so a second pointing up are flowing towards the northeast; those pointing down are flowing southwest. modeling phase was kicked off, cul- minating in a well-validated model as suggested in the excellent comparison shown in Figure 7. In the process, FSU discovered that the TRWs were being generated by the collision of the Loop (or a recently detached eddy) on the outer slope of the Mississippi Fan, just south of the Delta (Morey et al., 2010). With the successful validation of the model, DeepStar now had a tool that could be used to develop operational and extreme criteria. FSU developed the needed database by allowing the
22 Marine Technology Society Journal FIGURE 5 Finally, FSU recently started to apply their model results to develop a Cross section of the current meters deployed across the Sigsbee Escarpment. predictive capability that can even- tually forewarn drillers and installers of major facilities, of an approaching TRW that might threaten their op- erations. Initial results have shown that the numerical model cannot pre- dict the phase of TRWs very well since there are essentially no operational measurements in the lower deep water column available for model initializa- tion or data assimilation. Instead of direct use of the model, FSU is using the 50-year database to develop a sto- chastic model based on independent variables like the position of the Loop. This approach will not suffer the phase issues and should also provide uncer- tainty estimates.
Hurricane Winds In 2010, DeepStar funded a study model to free run for a 50-year period. the northern Caribbean and portions to bring together all available hurricane It was a daunting computation ef- of the southeast Atlantic. Figure 8 wind data sets made in and around the fort since it involved running a high- shows the model domain. Results from Gulf since 1998, quality control them, resolution (800 m grid size) nested the 50-year run were archived and are and then analyze them in an effort to model covering the Sigsbee Escarp- now being used by the Industry to check the validity of the present Amer- ment inside a 3.5 km model covering develop design criteria. ican Petroleum Institute (API, 2012) FIGURE 6 recommended equations for hurricane winds. The data sets included dozens Location of current measurements taken during 2008-2009. The dark blue curve shows the base of offshore platform anemometer re- of the Sigsbee Escarpment. cords, measurements from National Oceanic and Atmospheric Administra- tion (NOAA) buoys, Coastal-Marine Automated Network (C-MAN), Auto- mated Surface Observing System (ASOS), and National Ocean Service (NOS) stations, tower arrays of ane- mometers deployed along the coast, coastal weather radars, and dropsonde observations made by hurricane hunter aircraft. The first phase of this study was completed in 2012 by Applied Research Associates, Inc., Texas Tech Univer- sity, and the University of Florida
May/June 2013 Volume 47 Number 3 23 FIGURE 7
Comparison of model and observed current at three depths taken at one of the moorings shown in Figure 6.
and identified deficiencies in the API (ESDU, 1974, 1982, 1983) calculated (30–60 m). Such a discrepancy trans- (2012) equations for gust factors, pro- profiles. While the API (2012) pro- lates to more than 20% in the static files, and spectra when applied to hur- file compares well within a few 10 s drag force. On the other hand, the API ricanes. Figure 9 compares measured of meters of the sea surface, a 10% dis- (2012) equation for gust factors was speed profiles to the API (2012) and crepancy appears at the higher eleva- found to underestimate the observa- Engineering Sciences Data Unit tions typical of platform deck heights tions as shown in Figure 10. The second phase of the study is now underway, with the analysis ex- FIGURE 8 tended to tropical storm wind records made off the northwest coast of Contours showing the sea surface height over the large-scale (3.5 km) model. Insert shows the Australia, the east coast of the United nested model around the Sigsbee Escarpment with a resolution of 800 m. States, and a reexamination of the orig- inal Norway extratropical wind mea- surements used to develop the API relationships. The end goal of this phase is a revised set of wind design re- lations that may then be incorporated into the latest offshore standards, for both tropical and extratropical storms. The study is anticipated to be com- pleted by late 2013.
Summary and Conclusions In 1998, DeepStar began what was to become a highly insightful set of proj- ects in the field of meteorology and oceanography (metocean). The first project focused on measuring the
24 Marine Technology Society Journal FIGURE 9
Comparison of measured wind profiles with recommended profiles from API and ESDU for three different central pressure bins.
FIGURE 10
Comparison of measured gust factors with recommended factors from API and ESDU for three different wind speeds.
May/June 2013 Volume 47 Number 3 25 flow of the Loop Current through the work to analyze the wealth of wind ments in a Gulf of Mexico warm-core ring. Yucatan Straits—fundamental infor- data collected during the recent extreme In: Proc. 26th Int. Conf. on Offshore Mech. mation that had never been gathered. hurricanes. This study has revealed that and Arctic Eng., OMAE2007-29231. This was followed by measurements of the present Industry standard for hurri- New York: American Society of Mechanical turbulence in the Loop Current; a study cane wind spectra, profiles, and gusts Engineers. driven by concerns about resonance can be improved, so revisions will soon Morey, S.L., Dukhovskoy, D.S., & Cooper, C. in tendons, moorings, and risers. Field be adopted. 2010. Measurement and modeling of topo- measurements were completed in graphically trapped waves along the Sigsbee 2003, which dismissed that concern. Escarpment. In: Proc. Offshore Tech. Conf., In 2004, attention was turned to find- Corresponding Author: 20694. doi:10.4043/20694-MS. ing the best available forecast model of Cortis Cooper the Loop Current, a tool that could Chevron Energy Technology Co. save the Industry millions of dollars Email: [email protected] by helping it avoid downtime during drilling and installation of large facili- ties like spars. Two studies were done References comparing the ability of eight existing Abascal, A.J., Sheinbaum, J., Candela, J., Ochoa, J., & Badan, A. 2003. Analysis of forecast models. Results showed that flow variability in the Yucatan Channel. many of the models were much J Geophys Res. 108(C12):3381. doi:10.1029/ worse than simply assuming that the 2003JC001922. Loop remained unchanged (persis- tence) and revealed that the models American Petroleum Institute. 2012. were primarily limited by the accuracy Derivation of metocean design and operating of their initial conditions. This knowl- conditions, API RP 2MET, First Edition. edgehasbeenusedinotherIndustry Engineering Sciences Data Unit, ESDU. efforts to improve forecast models. In 1974. Characteristics of atmospheric turbulence 2004, a six-phase effort was begun to near the ground, Item No. 74031, London. quantify Topographic Rossby Waves Engineering Sciences Data Unit, ESDU. — (TRW) awavewithalengthof 1982. Strong winds in the atmospheric fi 200 km rst measured in the Gulf boundary layer, Part 1: Mean hourly wind in 1998 and capable of generating speed, Item No. 82026, London. currentsof1m/s(2kt)nearthesea Engineering Sciences Data Unit, ESDU. floor. Phases 1 and 2 deployed arrays 1983. Strong winds in the atmospheric of current meters that recorded several boundary layer, Part 2: discrete gust speeds, TRWs. These measurements were Item No. 83045, London. then used to develop and validate a numerical model—the first to success- Dukhovskoy, D.S., Morey, S.L., Martin, ’ fully simulate the full strength of these P.J., O Brien, J.J., & Cooper, C. 2009. powerful waves. Phase 5 used the TRW Application of a vanishing, quasi-sigma, vertical coordinate for simulation of high-speed, deep model to develop a 50-year hindcast currents over the Sigsbee Escarpment in the database that provides accurate oper- Gulf of Mexico, Ocean Model. 28(4):250-65. ational and extreme current criteria throughout much of the deepwater Hamilton, P., & Lugo-Fernandez, A. 2001. Gulf. Phase 6 is using the model to Observations of high speed deep currents in develop a probabilistic forecast that the northern Gulf of Mexico. Geophys Res can warn drill rigs and installation Lett. 28:2867-70. operations of an approaching TRW. Mitchell, T.M., Lueck, R.G., Vogel, M.J., & Most recently, DeepStar has funded Forristall, G.Z. 2007. Turbulence measure-
26 Marine Technology Society Journal PAPER Recent Development in IR Sensor Technology for Monitoring Subsea Methane Discharge
AUTHORS ABSTRACT Mark Schmidt Recently developed methane sensors, based on infrared (IR) absorption tech- Peter Linke nology, were successfully utilized for subsea methane release measurements. GEOMAR Helmholtz Centre for Long-term investigation of methane emissions (fluid flux determination) from nat- Ocean Research Kiel, Kiel, Germany ural methane seeps in the Hikurangi Margin offshore New Zealand were performed Daniel Esser by using seafloor lander technology. Small centimeter-sized seep areas could be CONTROS Systems & Solutions sampled at the seafloor by video-guided lander deployment. In situ sensor mea- GmbH, Kiel, Germany surements of dissolved methane in seawater could be correlated with methane con- centrations measured in discrete water samples after lander recovery. High backscatter flares determined by lander-based Acoustic Doppler Current Profiler Introduction (ADCP) measurement indicate bubble release from the seafloor. Highest methane atural marine hydrocarbon seeps concentrations determined by the IR sensor coincided with periods of high ADCP fl are important sources of methane backscatter signals. The high uid release cannot be correlated with tidal changes N only. However, this correlation is possible with variability in spatial bubble release, (CH4) to the surface sediments, the benthic boundary layer, and eventually sudden outbursts, and tidal changes in more quiescent seepage phases. to the water column and atmosphere. A recently developed IR sensor (2,000 m depth-rated) with a detection limit for methane of about 1 ppm showed good linearity in the tested concentration range CH4 is a potent greenhouse gas that warms the Earth about 23 times more and an acceptable equilibration time of 10 min. The sensor was successfully oper- than carbon dioxide (CO )whenaver- ated offshore Santa Barbara by a small work-class ROV at a natural methane seep 2 −1 aged over 100 years. Quantifying the (Farrar Seep). High background methane concentration of 50 nmol L was observed in the coastal water, which increases up to 560 nmol L−1 in dissolved discharge of CH4 from the seabed, itsfateinthewatercolumnandits methane plumes south of the seepage area. ROV- and lander-based sensor deploy- flux to the atmosphere has been the ments have proven the applicability of IR sensor technology for the determination of subject of ongoing research on many subsea methane release rates and plume distribution. The wide concentration different fronts (e.g., Clark et al., range, low detection limit, and its robust detection unit enable this technology 2000; McGinnis et al., 2006; Judd for both subsea leak detection and oceanographic trace gas investigations. & Hovland, 2007; Westbrook et al., Keywords: methane, sensor development, natural hydrocarbon seeps, subsea leak 2009; Faure et al., 2010). Furthermore, detection a natural subsea hydrocarbon seep can serve as an ideal analogon for studying gas leakage scenarios from subsea con- 2011; Schneider von Deimling et al., New Zealand. The second one was a structions like gas/oil transport lines, 2010). Here, we report on the devel- shallow water test of ROV-operated active or abandoned wellheads, etc. opment and deployment of novel sensor measurement at a natural hydro- (Leifer et al., 2006). Moreover, the dis- methane sensors, based on infrared carbon seep offshore Santa Barbara, solution behavior and transport of gas absorption technology, which were California. in the water column at variable ocean- tested in two different subsea settings. ographic conditions, like currents, The first setting was a long-term mul- horizontal/vertical eddies, tidal changes, tisensor deployment with a benthic CH4 Sensor Deployment or stratified water columns can be stud- lander, which was placed for 41 h at on a Deep Sea Lander ied at natural seepage sites (e.g., Leifer a 670-m-deep CH4 cold-seep at the A novel methane sensor HydroC™ et al., 2006; McGinnis et al., 2006, seafloor in the Hikurangi Margin, of CONTROS System & Solutions
May/June 2013 Volume 47 Number 3 27 GmbH, Germany, was deployed on FIGURE 1 a benthic lander equipped with a Overview map showing the bathymetry of the Hikurangi Margin at the east coast of New Zealand, wide range of instrumentation to mapped during R/V SONNE cruise SO191 in 2007 (modified from Linke et al., 2010). The enlarged study the role of physical parameters bathymetric maps depict the Rock Garden area with stations relevant for this paper; for example, on exchange processes in the benthic the site of vigorous gas discharge (Faure bubble site) discovered during a ROV dive (Naudts boundary layer. Benthic landers pro- et al., 2010) and two other lander stations (FLUFO-4 and BIGO-4) described in Linke et al. (2010). vide a stationary study platform de- (Color version of figures are available online at: http://www.ingentaconnect.com/content/mts/ mtsj/2013/00000047/00000003.) coupled from the movement of the ship and simultaneously measure sev- eral physical, chemical, and biological parameters across the sediment water interface. The Fluid Flux Observatory (FLUFO) was deployed for in situ flux measurements of methane and oxygen in about 670-m water depth at a meth- ane seep setting known as Rock Garden by local fishermen (Figure 1). This area is situated at the southern termination of Ritchie Ridge and is uplifted by the subduction of a seamount beneath the outer Hikurangi Margin at the east coast of New Zealand’s North Island. Townend (1997) estimated that more than 20 m3 of fluids are being squeezed from accreted and subducted sediments along each meter of the Hikurangi Margin every year, which results in abundant evidence of escaping gas off- shore (Faure et al., 2010; Linke et al., 2010; Naudts et al., 2010) and onshore (Campbell et al., 2008). The deploy- ment was part of a large campaign in- volving a large range of equipment and scientific disciplines to study the meth- ane seeps at the Hikurangi Margin (Greinert et al., 2010). The observatory consists of a ti- tanium tripod frame that carries 21 Benthos glass spheres for buoyancy and ballast weights attached to each leg (Figure 2a). The release of the ballast weights is controlled by two selected site at the seafloor (Pfannkuche berbymeansofglasssyringesam- acoustic releasers. FLUFO is equipped & Linke, 2003). Two to three hours plers. Sampling (monitoring) periods with two circular benthic chambers, after deployment, the benthic flux wereabout34(FLUFO-5)and40h each covering a sediment area of chambers were slowly driven into the (FLUFO-4, BIGO-4), respectively. 651.4 cm2. A video-guided launching sediment. Seabed methane emission After the in situ incubation, the bottom system (LAUNCHER) allowed smooth was monitored with eight sequentially of the chambers was closed with a shut- placement of the observatory on a water samples taken from each cham- ter to recover the sediments for further
28 Marine Technology Society Journal FIGURE 2 a parallel deployment of another lander (BIGO-4; Figure 2) at the same height Launch of the Fluid Flux Observatory (FLUFO) with the video-guided launcher on top showing the different scientific modules integrated in the back (a) and in the front (b) of the lander (modified above the sediment water interface like from Linke et al., 2010). the sensor showed two distinct peaks with CH4 concentrations of 189 and − 190 nmol L 1, respectively (Linke et al., 2010), which are in the same range of the measurements obtained with the HydroC™ sensor. On the other hand, the data shown here depict that the sensor needed some time of relaxation after it had experienced high a peak
of CH4 before it was able to record another sudden increase. However, the pulses seen in the HydroC™ sensor data correspond with analyses. After recovery, syringe water Acoustic Doppler Current Profiler increases in the backscatter strength de- samples retrieved during lander deploy- (ADCP; 300 kHz Workhorse Sentinel tected in all four beams of the upward- ment were immediately transferred into ADCP, Teledyne RD Instruments, looking ADCP (Figure 3d). The “flares” the cold room, where subsamples were USA) and a small stand-alone memory (presumed to be bubbles) persisted for obtained for the determination of oxy- CTD (Conductivity, Temperature, 10–60 min, and some of them covered gen and methane (Linke et al., 2010). Depth; XR420, RBR Ltd., Ottawa, almost the whole acoustic depth range Next to the chambers, the lander Canada). The CTD was also equipped (100 m) of the ADCP. No associated carried the HydroC™ methane sensor with an optical backscatter sensor signal was observed in the turbidity data for in situ measurements up to 4,000 m (SeaPoint), which measures light scat- obtained from the CTD (Figure 3a). water depths (Figure 2b). The high- tered by particles suspended in water. The occurrence of the flares does not pressure seawater side is separated by The lander was deployed in the seem to be related to a sudden or tidal a permeable membrane from the inter- vicinity of a methane gas vent named hydrostatic pressure drop (Figure 3c). nal infrared detection unit. An internal Faure bubble site (FLUFO-5; Figure 2). In fact, some of the outburst occurred pump system increases equilibration of Here, bubble release occurs from dif- during high tide and at maximum cur- − internal partial pressure of, for example, ferently sized depressions, which are rent velocities of more than 20 cm s 1 methane with the dissolved methane in often aligned in NW-SE direction; the (Figure 3b). This is in agreement with seawater. Concentrations of methane largest depression observed by a ROV results of Linke et al. (2010) from an- were determined by using optical was 50 cm in diameter and 15 cm deep other lander deployment next to the NDIR absorption technique. Large (Naudts et al., 2010). These observa- FaureSite(FLUFO-4;Figure2).They fl quantities of methane accumulated in tions clearly showed that the depres- found CH4 concentration uctuations the internal gas circuit can actively be sions are formed by the often violent in both the ambient bottom water and removed with a patented exhaust sys- release of bubbles. Naudts and cowork- the chamber water, which coincided tem. The sensor was calibrated to detect ers observed that the bubbles entrained with tidally induced fluctuations of CH4 concentrations as low as approxi- sediment particles, which then get car- currents and acoustic backscatter flares − mately 100 nmol L 1,anddatawere ried away by the water currents, creat- in the ADCP record. logged by a 24-bit SmartDI controller. ing the depressions and a sediment Furthermore, these measurements The HydroC™ methane sensor outfallawayfromtheventinghole. agree very well with ROV observations was mounted upright at the lander The data obtained with the HydroC™ in the area reporting highly variable frame to avoid any trapping of gas bub- sensor depict pulses of CH4 emission spatial bubble release rates and bubble bles in front of the membrane inlet. (Figure 3a), ranging between 150 and sizes, with periods of low activity, alter- − Beside the methane sensor, FLUFO 200 nmol L 1. Water samples obtained nating with periods of violent out- was equipped with an upward-looking from the ambient bottom water during bursts (Naudts et al., 2010).
May/June 2013 Volume 47 Number 3 29 FIGURE 3
Physical measurements obtained simultaneously to the changes in CH4 concentration during deployment of FLUFO-5. Top to bottom: (a) turbidity changes and CH4 concentration, (b) depth-averaged velocity time series, (c) local hydrostatic pressure, and (d) ADCP backscatter (all four beams).
trace gas (i.e., CH4) investigations in excellent detection limits at good High-Sensitive Methane the oceans and for subsea leak detec- signal-to-noise ratios. The actual Sensor (HISEM) tion, is currently under development configuration is a 2,000-m depth-rated Development (www.martec-era.net). The sensor version with a (Contros HydroC™) A new methane sensor, which technology is based on laser diode IR membrane-inlet configuration. The should fulfill the needs for scientific absorption technology that provides system was tested in the laboratory
30 Marine Technology Society Journal against various partial pressures of Gas exchange with atmosphere is pre- The detection limit of the HISEM of methane dissolved in water in a tem- vented in the semiclosed system. The about 1 ppm could be determined with perature controlled (4–15°C) water- response of the sensor signal is con- a signal-to-noise ratio of 5. filled calibration tube. The water tinuously recorded during testing, and The sensor output (ppm unit) shows is continuously equilibrated at atmo- equilibration of the signal is established good linearity (R2 = 0.99998) against t spheric pressure with standard gas mix- with a response time ( 65) of about the known pressure bottle concentra- tures of methane (3–200 mol-ppm) in 10 min after partial methane pressures tions given in mol-ppm with an offset synthetic air pressure bottles (∼200 bar). have been changed in the tube (Figure 4). of ∼1 ppm (Figure 4). The correlation
FIGURE 4
Methane concentrations determined with the HISEM system, which was placed in a water-filled calibration tube at 4°C. The water is equilibrated with methane by using different gas mixtures (3, 5, 11, 50, 100, and 200 mol-ppm CH4 in pressure bottles).
May/June 2013 Volume 47 Number 3 31 was confirmed by parallel determina- FIGURE 6 tion of dissolved methane concentra- (a) Deployment of the HYSUB 20 ROV from the starboard site of M/V Danny C. (b) The HISEM tions sampled from the calibration prototype (marked by white rectangle) was mounted behind the bumper bar of the ROV. tube. These methane analyses were conducted by using head space sam- pling technique and subsequent gas chromatographic analysis.
HISEM Offshore Test Site To test the sensor performance for methane plume detection and its offshore practicability in operating terized by low seepage activity, and the To measure dissolved methane the system with a small work-class re- gas composition of bubbles emanating concentrations during ROV dives, the motely operated vehicle (i.e., HYSUB from the seafloor consists of up to 90% HISEM system was mounted parallel 20 ROV), a 3-day offshore campaign of methane and 10% of higher hydro- behind the upper bumper bar of the was performed in November 2012 carbons (e.g., Leifer et al., 2006). As HYSUB 20 (Figure 6). The head (mem- near Santa Barbara, Southern Califor- gas bubbles dissolve and exchange brane inlet) of the HISEM prototype nia. The offshore test site that was cho- their gas content during uplift in sea- was connected with a plastic tube to a sen is named Farrar Seep and is located water, dissolved gas plumes are formed suction inlet at the front of the ROV. A within the Coal Oil Point seep area in in the water column and the initial hydro- metal filter was mounted to the suction the inner Santa Barbara Channel (Fig- carbon content of the bubbles decreases inlet, and the inlet area was monitored ure 5a) about 1,300 m east of the Uni- (e.g., Leifer & Patro, 2002; Clark et al., permanently by cameras. A second versity of California, Santa Barbara 2003; McGinnis et al., 2006). Numer- tube connected the suction inlet by a area (Figure 5b). The Farrar Seep is a ous natural gas and oil seeps exist in y-adapter with a CTD and a commer- natural hydrocarbon seep that is indi- the inner Santa Barbara channel, which cial leak detection device (Combination cated by gas bubble release from the lead to general high background con- of HydroC-CH4, Fluorometer). A seafloor at about 22 mbsl. Natural centrations of dissolved methane in constant water flow through the tubing − gas seeps in the area of the inner thearea(e.g.,∼20–100 nmol L 1; was guaranteed by two Seabird pumps, Santa Barbara Channel can be charac- Clark et al., 2000). which operated inline the tubes.
FIGURE 5
(a) Map of the overall area of the Santa Barbara channel in Southern California. The test site is marked as a small open circle. (b) Farrar Seep offshore test site (shaded rectangle), about 1,300 m east of the University of California Santa Barbara area.
32 Marine Technology Society Journal ROV-Based FIGURE 7 Sensor Measurements ROV dive tracks conducted in the test area “Farrar Seep.” Two N-S and four W-E ROV dives were conducted at the 28th and 29th of November 2012 at the estimated lo- cation of the Farrar Seep (Figure 5b). TheaveragelengthofaROVdive track was about 250 m. Furthermore, one vertical dive track was conducted at the estimated center of the seep (Fig- ure 5b). During all dives, water depth, temperature, conductivity (SV48 CTD, Sea and Sun Technology) and methane sensor data (HISEM) were recorded continuously. However, the ROV stopped every 15 m for 1–2minto increase the total measuring time. The homogeneous temperatures of about 15.8°C and salinities of about 33.4 PSU measured during the ROV dives indicate a well-mixed water column in this coastal area during November 2012. The water depth of FIGURE 8 the test area is about 16–30 mbsl and Methane sensor signal recorded with HISEM about 2 m above the seafloor during ROV track line 1 ROV dive tracks plotted in Figure 7 fi fl at the 28th and 29th of November 2012. Track line 1 is the N-S pro le and crosses the Farrar Seep were performed above sea oor at ele- (Figure 3). vations of 2 and 12 m, respectively. Due to strong currents in the area and especially a current direction and cur- rent speed change between the 28th and 29th of November 2012 (Goleta Point buoy data, SCCOOS.org), nav- igating the ROV was challenging and deviations from predefined track lines were about 15 m. The Farrar Seep loca- tion could be verified at 119°49.836′W and 34°24.157′N (WGS84) by mea- suring a CH4 concentration maximum − (up to 260 ppm and 334 nmol L 1, respectively) while crossing the cen- tral seepage site with the ROV at 2 m elevation above seafloor (Figure 8). The minimum concentration of dis- solved methane, which was determined in water masses in the test area, was − ∼50 nmol L 1. The center of the main seepage activity of the Farrar Seep was also
May/June 2013 Volume 47 Number 3 33 FIGURE 9
Spatial methane concentrations at Farrar Seep measured by HISEM during ROV dives. The concentration of methane is given in ppm. The total range measured by HISEM corresponds to dissolved methane concentrations of 50–560 nmol L−1 in the test area.
indicated by the ship’s echo-sounder 50–150 m around the seepage site technology. The technology, mea- (acoustic blankening by gas bubbles) (Figure 9). However, dissolved gas suring the partial pressure of methane and ground-truthing by ROV (video plumes with high methane concentra- in a separated gas chamber, is com- − observations). Note that measuring tions (up to 560 nmol L 1) were also bined with a membrane inlet, which the dissolved gas content within the examined towards the east and south separates high-pressure conditions bubble streams emanating from the at about 12 m above the seafloor (Fig- of the deep sea from the gas chamber seafloor did not increase the HISEM ure 9). In general, the dissolved meth- at normal pressure. Recent advances sensor concentration signal. The con- ane concentrations are highest towards in laser diode technology led also centration pattern of November 28th the south, which could indicate a pre- to cost-effective and high-sensitive could be verified by following the same ferred rotation of the methane plume infrared absorption units. The newly track on the 29th (Figure 8). The devi- direction from east to south and then designed high-sensitive methane sen- ation of methane concentration data of west (Figure 9). sor (HISEM), which combines laser − about 25 nmol L 1 measured within diode infrared absorption with mem- the central seep area is possibly related brane inlet technology, closes a gap to a weakening of the local current re- Conclusions between the needs of small and less gime on the 29th (http://sccoos.org/). Subsea determination of dissolved sensitive methane sniffers used for The dimensions of the main (dis- methane concentration can be con- offshore leak detection (Oil & Gas solved) methane plume were about ducted by using infrared absorption Industry) and oceanographic trace gas
34 Marine Technology Society Journal − determinations down to 1–2 nmol L 1 Corresponding Author: Cambridge Univ. Press. 475 pp. http://dx.doi. org/10.1017/CBO9780511535918. of CH4 (equilibrium concentration of Mark Schmidt seawater with the atmosphere). GEOMAR Helmholtz Centre for Leifer, I., Clark, J., & Luyendyk, B. 2006. Membrane-inlet IR absorption Ocean Research Kiel Simulation of a Subsurface Oil Spill by a sensors can be used for long-term Wischhofstr. 1-3, Marine Hydrocarbon Seep. MMS OCS Study measurements at the seafloor (e.g., 24148 Kiel, Germany 2006-050. Santa Barbara, CA: Coastal lander-based deployment). The de- Email: [email protected] Research Center, Marine Science Institute, termination of, for example, varying University of California. MMS Cooperative methane concentrations in the vicinity Agreement Number 14-35-01-00-CA-31063. 81 pp. of a methane seep have to be combined References with determination of temperature, Leifer, I., & Patro, R.K. 2002. The bubble Campbell, K.A., Francis, D.A., Collins, M., mechanism for methane transport from the salinity, and pressure variations, as Gregory, M.R., Nelson, C.S., Greinert, J., shallow sea bed to the surface: A review and well with current measurements (i.e., & Aharon, P. 2008. Hydrocarbon seep- sensitivity study. Cont Shelf Res. 22:2409-28. using ADCPs). This combination is carbonates of a Miocene forearc (East Coast http://dx.doi.org/10.1016/S0278-4343(02) the basic information used to deter- Basin), North Island, New Zealand. Sediment 00065-1. mine (dissolved) gas fluxes from natu- Geol. 204:83-105. http://dx.doi.org/10.1016/ ral seeps or leaking constructions at j.sedgeo.2008.01.002. Linke, P., Sommer, S., Rovelli, L., & the seafloor. McGinnis, D.F. 2010. Physical limitations Clark, J.F., Leifer, I., Washburn, L., & fl Focused release of methane from of dissolved methane uxes: The role of Luyendyk, B.P. 2003. Compositional changes bottom-boundary layer processes. Mar Geol. subsea seeps and of rising plumes of in natural gas bubble plumes; Observations 272:209-22. http://dx.doi.org/10.1016/ dissolved methane can be monitored from the Coal Oil Point marine hydrocarbon j.margeo.2009.03.020. with ROV-based IR sensor technol- seep field. Geo-Mar Lett. 23:187-93. http:// ogy. However, the quantification of dx.doi.org/10.1007/s00367-003-0137-y. McGinnis, D.F., Greinert, J., Artemov, Y., Beaubien, S.E., & Wuest, A. 2006. Fate of methane release also needs some basic Clark, J.F., Washburn, L., Hornafius, J.S., & rising methane bubbles in stratified waters: oceanographic information about the Luyendyk, B.P. 2000. Dissolved hydro- How much methane reaches the atmosphere? local current regime and physical carbon flux from natural marine seeps to the J Geophys Res. 111:C09007. http://dx.doi. parameters (T, S, P) along the ROV Southern California Bight. J Geophys Res. org/10.1029/2005JC003183. dive tracks. This could be realized dur- 105(11):509-11,522. McGinnis, D.F., Schmidt, M., DelSontro, ing onboard CTD measurements and Faure, K., Greinert, J., Schneider von T., Themann, S., Rovelli, L., Reitz, A., & an upward-looking ADCP deployed Linke, P. 2011. Discovery of a natural CO2 fl Deimling, J., McGinnis, D.F., Kipfer, R., & at the sea oor. A miniaturization of Linke, P. 2010. Methane seepage along seep in the German North Sea: Implications the recently developed high sensitive the Hikurangi Margin of New Zealand: for shallow dissolved gas and seep detection. methane sensor (HISEM) is prere- Geochemical and physical data from the water J Geophys Res (Oceans). 116:C03013. quisite to use this technology onboard column, sea surface and atmosphere. Mar http://dx.doi.org/10.1029/2010JC006557. Geol. 272:170-88. http://dx.doi.org/10.1016/ inspection class ROVs. Naudts, L., Greinert, J., Poort, J., Belza, J., j.margeo.2010.01.001. Vangampelaere, E., Boone, D., … De Batist, M. Greinert, J., Lewis, K.B., Bialas, J., Pecher, I.A., 2010. Active venting sites on the gas-hydrate- Acknowledgments Rowden, A., Bowden, D.A., … Linke, P. bearing Hikurangi Margin, Off New Zealand: The HISEM system development 2010. Methane seepage along the Hikurangi Diffusive versus bubble-released methane. Mar is funded by the German Ministry Margin, New Zealand: Overview of studies in Geol. 272:233-50. http://dx.doi.org/10.1016/ BMWi (Project No. 03SX301) within 2006 and 2007 and new evidence from visual, j.margeo.2009.08.002. the European funding initiative bathymetric and hydroacoustic investigations. Pfannkuche, O., & Linke, P. 2003. MARTECH (ERA-NET, Maritime Mar Geol. 272:6-25. http://dx.doi.org/ GEOMAR landers as long-term observatories. Technologies). Wintershall Noordzee 10.1016/j.margeo.2010.01.017. Sea Technol. 44(9):50-5. is kindly acknowledged for support- Judd, A.G., & Hovland, M. 2007. Seabed Schneider von Deimling, J., Greinert, J., ing the offshore operations and ROV Fluid Flow: The Impact on Geology, Biology, Chapman, N.R., Rabbel, W., & Linke, P. adaptions. and the Marine Environment. New York: 2010. Acoustic imaging of natural gas seepage
May/June 2013 Volume 47 Number 3 35 in the North Sea: Sensing bubbles controlled by variable currents. Limnol Oceanogr Meth. 8:155-71. http://dx.doi.org/10.4319/lom. 2010.8.155.
Townend, J. 1997. Subducting a sponge: minimum estimates of the fluid budget of the Hikurangi margin accretionary prism. Geol Soc N Zeal Newsl. 112:14-6.
Westbrook, G.K., Thatcher, K.E., Rohling, E.J., Piotrowski, A.M., Pälike, H., Osborne, A.H., … Aquilina, A. 2009. Escape of methane gas from the seabed along the West Spitsbergen continental margin. Geophys Res Lett. 36:L15608. http://dx.doi.org/10.1029/ 2009GL039191.
36 Marine Technology Society Journal PAPER Development of the Jiaolong Deep Manned Submersible
AUTHOR ABSTRACT Weicheng Cui Deep sea exploration and exploitation are of increasing interest to 21st century Hadal Science and Technology scientists, and both manned and unmanned deep submergence vehicles are Research Center, necessary means for deep sea exploration. To fulfill the requirements of deep sea Shanghai Ocean University, exploration for China Ocean Mineral Resources R&D Association (COMRA), a deep Shanghai, China and manned submersible was in the process of development in China from 2002 to fi China Ship Scienti c Research 2012 and was named Jiaolong in 2010. The purpose of this paper is to introduce Center, Wuxi, Jiangsu, China the development process from a historical point of view, including the design, realization of components, assembly, open-water tank test, and sea trials of the Jiaolong deep manned submersible. The technical difficulties encountered at Introduction each stage, and their solutions are briefly described. The future development trends he deep seas have fascinated hu- for deep manned submersibles are pointed out. Jiaolong mans for centuries. The flow of new Keywords: deep manned submersible, , development process, design, T realization of components ideas has traveled through the centuries and inspired people to dive below the surface and explore the forms of life that exist in the abyss. A detailed histor- cles (AUVs) and remotely operated respectively. In the 1990s, Russia ical account of human beings’ deep dives vehicles (ROVs) have advantages in started to develop two more 6,000-m into the oceans and discovery of its true certain aspects, Human operated vehi- submersibles, Rus and Consul,that mysteries can be found in, for example, cles (HOVs) remain the central ele- were to be fully built in country. Due Forman (2009), Kohnen (2009), and ment in the selection of modern tools to lack of funding, the sea trials of Sagalevitch (2009). Deep sea explora- at the service of knowledge acquisition these two submersibles were not tions are indispensable, not only for the (Kohnen, 2009; CFNDSC, 2004; completed until 2011, and both are investigation of marine creatures, micro- Rona, 2000) because the sense of vision now in service of the Russian Navy organisms, minerals, and other resources is the most important of all the five (http://www.rusnavy.com/news/). hidden under the deep water but also for human senses. The first proposal to develop a geophysical research into the structure In the 1970s and 1980s, the U.S. 6,000-m deep manned submersible and behavior of the earth. Deep sea ex- manned submersible DSV Alvin,made in China was submitted by the China ploration and exploitation are of increas- a number of important discoveries in Ship Scientific Research Center ing interest to people in the 21st century, marine scientific research (http://www. (CSSRC) to the then State Commission and both manned and unmanned deep whoi.edu/). This promoted an upsurge of Science and Technology (now the submergence research vehicles are neces- in the international community to Ministry of Science and Technology) sary means for deep sea exploration developdeepmannedsubmersibles. in 1992. Because the public demand (Momma, 1999; Committee on Future The first 6,000 m submersible was the for deep manned submersibles was Needs in Deep Submergence Science U.S. Navy’s Sea Cliff. France, the not urgent and the technical risk was [CFNDSC], 2004; Committee on Evo- former Soviet Union and Japan then high, the proposal was not approved. lution of the National Oceanographic developed another four 6,000-m deep In 1999, the China Ocean Mineral Research Fleet, 2009; Fletcher et al., manned submersibles, namely, Nautile Resources R&D Association (COMRA) 2009; Barry & Hashimoto, 2009). (Jarry, 1986), MIR I & II (Sagalevitch, submitted a new proposal for a deep Although unmanned submersibles 2009), and Shinkai 6500 (Nanba manned submersible, substantiating such as autonomous underwater vehi- et al., 1990; Takagawa et al., 1995), a pressing need for such technology
May/June 2013 Volume 47 Number 3 37 to fulfill their duties. This renewed existing submersibles, so the technical (12) underwater emergency jettison proposal was approved by the Ministry innovations and the application of the system. The principal challenge for of Science and Technology of the latest immature technologies were not such a division is the handling of inter- Chinese Government and marked the the emphasis of the project. Our de- face relations among numerous subsys- beginning of the deep manned sub- sign team began its formal design tems. The interface relations between mersible project now named Jiaolong. work in June 2002. According to the any two subsystems should not be COMRA was appointed as the project requirements of the quality control repeated or omitted, and this cannot coordinator and final owner of this manual of CSSRC, the design was di- be guaranteed simply by the chief submersible. The development for- vided into three phases: preliminary designer’s experience. Therefore, a mallybeganinJune2002,andon design, technical design, and detailed four-element method was developed June 30, 2012, the Jiaolong success- design. to solve this problem (Cui et al., 2008a, fully completed the final dive of its Having made an in-depth summary 2008b). All the parameters of each sub- sea trials program. of the missions and the overall technical system were divided into four categories: The purpose of this paper is to ex- indicators specified in the contract, the input, output, support, and restraint. amine the development process from a following five essential key performance The designers were asked to draw a historical point of view, including de- factors were proposed: four-element diagram for each subsys- sign, realization of components, assem- (1) the ability to reach a depth of tem to check the consistency (shown in bly, open-water tank test and sea trials 7,000 m; Figure 1). This allowed us to success- of the Jiaolong deep manned submers- (2) good maneuverability; fully handle and reconcile the interface ible. The paper will be divided into (3) the capability of real-time com- relationship among all 12 subsystems four sections. After the first introduction munication and microtopography in an orderly and systematic process, section, the entire development process detection; thus solving the first and most funda- of the submersible is described in Devel- (4) the capability to sample in a hov- mental problem for the development opment Process of the Deep Manned ering state at a designated position; of the manned submersible. Submersible Jiaolong. This process in- and The preliminary design was a sig- cludes the three stages of design, reali- (5) safety and reliability. nificant challenge for the design zation of components and assembly, After developing the five key perfor- team, since nobody had any personal as well as open-water tank test and mance factors, a list of technical chal- experience with a real deep manned sea trials. The technical difficulties lenges was identified for the research submersible. The components selec- encountered at each stage and their and production of the Jiaolong sub- tion, how to arrange them to form a respective solutions are also briefly mersible. This resulted in a selection coordinated and functional vehicle, described. Latest Technical Specifi- of key techniques for each of the per- and the weight and displacement of cations of the Jiaolong are listed and formance requirements. The chief de- each component were all unknown. Future Development Trends for Deep signer then divided the vehicle into Almost all the important pieces of Manned Submersibles are brieflydis- 12 subsystems according to the re- equipment for the Jiaolong ended up cussed in section 3. The last Section quirements of the overall technical being custom parts, which needed to is a summary, and some conclusions indicators and characteristics of the be developed specifically for us by the from the development process have participating research units and person- producers. Through communication been drawn. nel. The 12 subsystems were (1) the and discussion with the relevant pro- overall performance and general arrange- ducers, the performance, weight, and ment; (2) structure system; (3) outfitting; volume of each piece of equipment Development Process (4) ballast and trim adjustment system; gradually became clear. of the Deep Manned (5) propulsion system; (6) electric power In order to make each subsystem Submersible Jiaolong and distribution system; (7) lighting, work effectively and form a complete Design video, and VHF communication sys- entity, able to complete its missions The main purpose of the project is tem; (8) control system; (9) acoustic and tasks, the general arrangement of to develop a usable submersible, which system; (10) hydraulic and operation the manned submersible was devel- is of comparative performance with system; (11) life support system; oped with a modularized structure
38 Marine Technology Society Journal FIGURE 1 areas of the manned cabin, using the simple analysis method of fatigue life The four-element diagram of the system/subsystem. according to CCS rules (Li et al., 2006). This then provided the main structural parameters of the manned cabin. Next, a Russian company was contracted to produce the manned cabin using the “melon petals welding into a semi-sphere” method. After that, a pressure test was carried out in Russia. The pressure vessel was instru- mented with strain gauges, and mea- sured stress values were found to be in good agreement with the finite ele- ment analysis results. Based on this test data, we determined that our design was reasonable, the manufacturing quality was guaranteed, and the ultimate strength and fatigue life of the manned cabin of the Jiaolong was ensured. and function as a guideline. The key factors at openings, analyzing the ulti- However, we clearly knew that point of the design process was to en- mate strength, choosing the appropri- only a small number of manned sub- sure the reliability and maintainability ate safety factors, determining the mersibles had been produced in the of the submersible. fatigue load spectrum, and analyzing world, and most of them had been On February 26–27, 2003, the the fatigue life. developed by the navy and not classi- “Preliminary Design of the Jiaolong Due to time constraints, the team fied by classification societies. There- Manned Submersible” was submitted chose to follow the rules of the China fore, strictly speaking, the design to an experts’ review organized by the Classification Society (CCS, 1996) standards and safety assessment stan- State Oceanic Administration, and the and the Russian Maritime Register of dards of any classification society project entered into the phase of tech- Shipping (RS, 2004). Our objective lacked practical experience. Thus, the nical design. The research and design was to concurrently meet the two sets rationality and scientificfoundation at this stage were focused on feasibility, of rules. In addition, the finite element of the design standards needed to be reliability, and maintainability consid- method was used to analyze and calcu- investigated. erations. A mature design state was late the ultimate strength of the manned In the development of the Jiaolong reached, in which the main technical cabin (Lu et al., 2004). Specific atten- submersible, 40% of the equipment indicators of the submersible were tion was paid to stress concentrations was procured from international com- fixed, through modeling and proto- near large openings, such as personnel panies. In order to expand deep sea type testing. access hatches, observation windows, technology development in China, a Designing the manned cabin was and penetrators. The use of the finite new project to construct a domestically technically difficult because it was element method with contact elements produced 4,500 m manned submers- directly related to the safety of the to analyze this problem was partic- ible was started in 2009. The main ob- crew. If the design was too conserva- ularly helpful (Li & Cui, 2004). jectives of this project were to reduce tive, the submersible would be very The fatigue design load spectrum the operational cost and to further in- heavy, undermining its maneuver- was first proposed through a statistical crease the reliability, in addition to the ability and increasing the operational analysis of the Alvin manned submers- technology development. cost. To find a safe balance, a series ible’s historical dive data (Li et al., This compelled the team to com- of problems needed to be solved, such 2004). Based on this, we analyzed the pare the design standards of all major as calculating the stress concentration fatigue life of the stress-concentrated classification societies; they found that
May/June 2013 Volume 47 Number 3 39 the strength requirements of these TABLE 2 design standards varied widely. In Check of actual designs of existing pressure hulls to the existing design rules. fact it was noted that most existing deep manned submersibles could not Consul Shinkai New a meet the requirements of the pub- Submersible Alvin (Rus) Nautile 6500 Alvin Jiaolong lished standards, see Table 1 and DNV1988 XXXXXX Table 2 (Pan & Cui, 2011a, 2011b). BV1989 XXXXXX Considering that all these submersibles LR1989 XXXXXX operated safely in the past years, most √√√ classification societies’ standards can RS2004 X XX be considered overly conservative for CCS1996 X √√XXX hadal depth designs. ABS2009 XXXXXX Hence, we reviewed the analysis GL2009 XXXXXX method of the buckling and ultimate aNote: Due to the lack of detailed material data for each submersible, the average material properties for strength of spherical pressure hull Titanium TA6V4 have been employed in the calculations made in Table 1. Dr. Jean-Francois Drogou from under external pressure (Pan & Cui, IFREMER pointed out in the review process that, for Nautile, the TA6V4 alloy is forged in beta phase that gives fi 2010), unified the description meth- a resistance Re0.2 of more than 950 MPa and the design of Nautile hull satis ed with the ABS requirements. ods of the initial defects, made a series of calculations about all the parameters the U.S. Navy’s requirements for the ten into their “Principles of Check of affecting the ultimate strength of the control methods of macro stress lev- Drawing and Inspection of Deep-Sea manned cabin within the range of els and stress concentration (NSSC, Manned Submersible” (CCS, 2011) possible variations by finite element 1998), a set of complete design stan- as the classification standard for the analyses, and, finally, proposed a dards for a manned cabin was pro- Jiaolong. The new design standard of more rational ultimate strength for- posed (Pan & Cui, 2011a, 2011b). the manned cabin is as follows (Pan mula (Pan et al., 2010). By absorbing These were adopted by CCS and writ- & Cui, 2011a, 2011b).
TABLE 1
Calculation results of existing titanium pressure hulls.
Actual Design of Existing Pressure Hull
Submersible Alvin Consul (Rus) Nautile ShinKai 6500 New Alvin Jiaolong Depth (m) 4,500 6,000 6,000 6,500 6,500 7,000 Operating pressure from 45.45 60.6 60.6 65.65 65.65 70.7 GL2009 (MPa) Internal diameter (m) 2.0 2.1 2.1 2.0 2.1 2.1 Design thickness (mm) 49 71 62–73 75 71–72 76–78 Safety factor 1.5 1.5 1.5 1.55 1.5 1.5 Minimum proof thickness calculated by design rules (mm) DNV1988 59.7 78.2 78.2 79.5 83.5 88.7 BV1989 62.6 86.9 86.9 90.4 94.9 103.0 LR1989 75.6 99.0 99.0 101.0 106.1 113.4 CCS1996 51.5 72.7 72.7 77.8 78.9 85.2 RS2004 51.1 68.9 68.9 72.7 74.0 79.2 GL2009 59.4 83.2 83.2 86.1 90.2 97.8 ABS2010 72.0 97.6 97.6 103.3 105.1 112.9
40 Marine Technology Society Journal The ultimate strength of the titanium alloy spherical pressure hull of deep hydrodynamic performance, deter- manned submersible is calculated by the following equations: mined the properties of judging its comprehensive hydrodynamic perfor- Δ σut σut mance,andprovidedanoptimized Pu ¼ 1 k þ ð1Þ R R Rm design method for the manned sub- mersible’s hydrodynamic performance ! under constraints. When studying Δ t Δ 2 t 2 Δ 3 t 3 k ¼ a þ b exp c d þ e þ f g h ð Þ the spatial hydrodynamic characteris- × R R R R R R 2 tics of a deep manned submersible in a complex nonlinear deep sea environ- where a = −15.63; b = 606.6; c = 264.6; d = 72.72; ment, the submersible’s hydrodynamic e =3×104; f = 882.5; g = 1.2 × 106; h = 3969; characteristic of a 6 degree-of-freedom σu = the guaranteed minimum tensile strength of titanium alloy used; motion was obtained. An equation of t = thickness of the pressure hull; a 6 degree-of-freedom spatial motion R = internal radius of the spherical pressure hull; was derived, the corresponding hydro- Rm = mean radius of the hull. dynamic coefficients were determined Δ = the deviation between actual spherical surface and regular spherical surface. from wind tunnel tests, rotating arm The application range of this empirical equation is 0.025 ≤ t/R ≤ 0.08 and basin tests, towing tank model tests, Δ/R ≤ 0.01. The safety factor for this equation is 1.5. and a mathematical model was estab- Besides the above ultimate strength formulae, additional stress limitations that lished, which can be used to forecast control the overall stress level and local stress concentrations need to be considered and analyze the submersible’s maneu- in the makeup of a safety standard. The stress limitations are suggested to be as verability (Ma & Cui, 2004, 2005, follows: 2006a, 2006b; Cui & Ma, 2009; Pan a. The average shell membrane stress at maximum operating pressure shall be et al., 2010). limited to two thirds of the minimum specified yield strength of the material. The ballast and trim regulating sys- b. The highest combined value of average shell membrane stress and bending tem consists of a variable ballast system stress (excluding effects of local stress concentrations) at maximum operating with a flow rate of up to 3 L/min, one pressure shall be limited to 3/4 of the minimum specified yield strength of the ballast tank with displacement of up material. to 1,500 kg and a set of trim regulat- c. The maximum compressive peak stress at any point in the hull, including ef- ing systems with a flow rate of up to fects of local stress concentrations, shall be limited to 4/3 of the minimum 15 L/min. The variable ballast system specified tensile yield strength and shall not exceed the compressive ultimate consisted of a titanium sphere 840 mm strength of the material. The maximum tensile peak stress at any point in the in diameter, a hydraulically operated hull, including effects of local stress concentrations, shall be limited to the min- super-pressure pump, driven by an imum specified yield strength of the material. 8-kW DC motor, oil-immersed sole- d. Currently, there is no condition to set a reliable standard for fatigue strength noid valve, pressure balance valve, etc. assessment. It is recommended that designers and users of the submersible Commercial companies were commis- should pay attention to this issue and carry out the fatigue analysis at all stress sioned to produce a super-pressure concentration areas using the commonly accepted approaches. pump and DC motor. The trim regu- This newly established safety standard was used to optimize the structural lating system mainly consisted of tanks design of the 4,500 m manned cabin (Pan & Cui, 2012). located at the bow and aft, an oil con- To solve the problem of a comprehensive optimized design for Jiaolong’s trol box (containing oil pump, oil hydrodynamic layout and lines, we systematically collected a comprehensive motor and valves) and a piping system. amount of relevant data of all the submersibles in the world, analyzed their charac- The trim regulating system’spower teristics of shape and hydrodynamic performance, proposed assessment indicators came from the submersible’s hydraulic of the submersible’s maneuverability, established theoretical and experimental fore- source; the oil motor used the power casting methods for its hydrodynamic performance (including speed and maneu- of the hydraulic source to drive the verability), clarified the main design variables of the manned submersible’s low-pressure oil pump to provide
May/June 2013 Volume 47 Number 3 41 low-pressure oil of 1.5 MPa, which the life support system. In addition, system included two hydraulic manip- pumped the mercury back and forth when the submersible is floating at ulator arms, a hydrothermal sampler to between the bow and aft, thereby ad- the surface, the spare battery provides keep high-pressure liquid, a sediment justing the trim angle. a VHF radio transmitter and strobe sampler, underwater drilling equip- The propulsion system was com- lights. The emergency battery electric ment, and a sampling basket. posedoffourmainductedpropellers capacity is 5.4 kwh. Themainfunctionofthecontrol at the stern, two rotatable ducted pro- Lighting and video equipment system is to collect information from pellers midship, and one tunnel pro- serve to provide a source of underwater sensors on the submersible, display peller at the bow. According to the lighting for operators and observers and record the data and then control contract, the submersible had to have when sailing, operating and observing. the implementation mechanisms. This a maximum speed of up to 2.5 km Video equipment serves to photograph makes the submersible competent to and a cruising speed up to 1 km. underwater targets and then stores the cruise, observe, and perform tasks. The electrical power and distribu- videos and photos. The main role of The acoustic system is mainly com- tion system supplied electrical power the VHF communication system is to posed of an underwater acoustic com- to the whole submersible. Thus, it offer radio voice communication on municator, high-resolution side-scan should have the following functions: the surface. Originally, the Jiaolong sonar, acoustic Doppler speedometer, providing 110 V DC to the thruster was equipped with one 3CCD color obstacle avoidance sonar, imaging motors, hydraulic source motor, and video camera, two 1CCD color video sonar and long-distance ultra-short various lights outside the submersible; cameras, one black-and-white low- baseline positioning sonar. Installed providing 24 V DC to underwater light level video camera, one underwa- on both sides of the submersible, the acoustic equipment, motion control ter camera, two HMI lamps, two HID high-resolution side-scan sonar is system, sensors and instruments in lamps, four quartz halogen lamps, one used to measure the seabed’smicro- the cabin, etc.; having the ability to pan and tilt, and one set of video cam- topography and targets in the water supply sufficient power for the whole eras in the cabin. After the 3000-m- or on the seabed and draw real-time submersible according to the require- depth class sea trials, the lighting and three-dimensional maps of the scene. ments of the power consumption of camera systems were upgraded. The The mechanical scanning imaging all the equipment and time history of Jiaolong is now equipped with 10 LED sonar is located at the bow of the sub- typical missions; offering a distribu- lamps, 4 HMI lamps, 2 HID lamps, mersible and serves to detect the sur- tion switch and protection for the 1 quartz halogen lamp, 2 HD video rounding environment and forward main power supply circuit. Accord- cameras, 2 1CCD video cameras, targets in the water for the pilot’sob- ing to the requirements of the sub- 1 camera, 1 black-and-white low- servation. On one hand, it helps the contract’s technical specifications, the light level camera, 2 pan and tilts, pilot to search for targets; on the other electrical power and distribution sys- 1 HD video recording system, and hand, it prevents the submersible from tem needed to equip a set of oil- 1 video camera in the cabin. running into obstacles, thus ensuring immersed silver-zinc batteries and The hydraulic system is the its safety. a set of corresponding distribution Jiaolong’s most important source Seven anticollision sonars are in- systems. of auxiliary power, since it supplies stalled at the bow and on both sides Based on the statistics of the load hydraulic power for buoyancy adjust- of the submersible. They are able to diagram, the load of the main battery ment, trim adjustment, and under- measure the distances between the was 86.7 kwh; that of the secondary water sampling. The hydraulic system submersible and obstacles in six di- battery was 24.2 kwh; thus, the total has rate of pressure up to 21 MPa, rate rections, helping the pilot to avoid ob- output capacity of the main and sec- of flow up to 25 L/min, and a maxi- stacles to ensure safety. They also ondary batteries should be not less mum input power up to 10 kW. measure the distance from the sub- than 110.9 kwh. The emergency The Jiaolong’s design requirements mersible to the seabed to control the battery is used if both the main and also included the function of a sam- submersible. secondary batteries fail and mainly pling system, to accomplish a series The Jiaolong is equipped with provides power to emergency lighting, of tasks relying on the power from a transponder at its top; thus, it can the underwater acoustic phone, and the hydraulic system. The sampling be positioned by the long-distance
42 Marine Technology Society Journal ultra-short baseline positioning sonar will certainly become positively (6) A rescue buoy: if the submersible installed on the mother ship. Further, buoyant and thus can go upward. is trapped on the seabed, the rescue the combination of this and the GPS is The emergency jettison system buoy will be released by detonat- able to provide the absolute position of wasdesignedtobeabletodrop ing electrical-explosive bolts. The the submersible. In addition, a long ballasts using two independent strobe light on the buoy will lead baseline system was added after the mechanisms, one electromagnetic the mother ship to find this buoy, 3000-m-depth sea trial. and the other hydraulic. Ballasts and then mother ship can catch the The life support system provides can be jettisoned by a single action. buoy and drag the submersible up
oxygen (O2) in three ways: normal op- What is more, as soon as a power by a cable, as long as 9,000 m, link- eration, emergency operation and oxy- failure starts, the ballast will be ing the submersible and the buoy. gen masks. Each oxygen subsystem is automatically discarded. (7) A mechanism used to jettison the independent of the others in order to (2) A main battery box jettisoning sampling basket: The sampling bas- ensure the system’sreliability.There mechanism: in a situation in ket is also connected with the sub- is one set of normal life support sys- which solid ballasts cannot be dis- mersible by an electrical-explosive
tems providing O2 for 12 h, one set carded, the main battery box that bolt,sothatifitisbound,itcan of emergency life support systems pro- weighs 1.2 tons will be discarded be jettisoned.
viding O2 for 60 h, and one set of mask so that the submersible can become On the basis of the general ar- breathing systems provide O2 for 12 h. positively buoyant. This function rangement drawings of the prelimi- These systems use high-pressure oxy- is realized through the use of two nary design, a 1:1 model was made to gen cylinders to produce oxygen and electrical-explosive bolts (one of test and confirm the maintainability high-efficiency lithium hydroxide to them offers redundancy) with a and rationality of the general arrange- absorb carbon dioxide. series connection. As long as one ments. The final configuration of the The Jiaolong is China’s first deep of them works, the main battery Jiaolong’s general architecture and the manned submersible. Consequently, box can be dropped. preliminary determination of its hydro- during the period of sea trials, China (3) A mercury jettisoning mechanism: dynamic performances were firmed did not have a rescue capability. There- all the mercury weighs 480 kg and up through repeated attempts and fore, safety was the most important can easily be jettisoned. However, modifications. concern for the Jiaolong at that time. jettisoned mercury will pollute On August 29–30, 2003, the In the design phase, we proposed the environment; therefore, this is “7000 m Manned Submersible’s “able to dive downward, able to come not encouraged unless in an emer- Technical Design” was submitted to back” as the design principle. The gency. In many cases, even if every- the expert review organized by the overall guiding philosophy was that thing else cannot be jettisoned, State Oceanic Administration and the Jiaolong should be fitted with all jettisoning the mercury will be received positive confirmation. the existing emergency means of exist- able to provide sufficient buoy- The detailed design phase involved ing manned submersibles. In addition, ancy to make the submersible go mainly the generation of construction we would ensure that the emergency upward. drawings on the basis of the technical jettison system was sufficiently reli- (4) A mechanism used to jettison the design, establishing a reliable supply able through numerous prototype hydraulic manipulator arms: if channel of each piece of equipment evaluations and sea trials. Having the manipulators are bound, they and doing model tests for critical pieces. learnt from the successful experience can be completely released. In this phase, the team also established of existing manned submersibles, the (5) A ballast tank system: when the a joint debugging test process and following self-rescue measures were submersible goes up to only 10 me- implementation method, technical implemented based on the idea of a ters below the sea surface, the pilot principles of assembly and an overall “redundant design”: should start the ballast tank system testing process. (1) A ballast jettisoning mechanism: to drain off water. This is capable of On April 13–14, 2004, the the maximum weight of the solid providing 1.5 tons of buoyancy, “Detailed Design of the 7000 m ballast is 1.3 tons. As long as it jet- ensuring that the Jiaolong has a rel- Manned Submersible” was submitted tisons all of them, the submersible atively large freeboard on the water. to the expert review set by the State
May/June 2013 Volume 47 Number 3 43 Oceanic Administration and received China’sexemptionpolicywasnot matched the steel frame, they did not acceptance. clear, the customs formalities for our match the titanium frame. Hence, the imported equipment were not com- interface between the brackets and tita- Realization of Components pleted until September 2006. On nium frame needed to be repeatedly It was very difficult for China to September 25, 2006, the last piece of modified. What is more, oxygen cut- produce some of the equipment for imported equipment reached CSSRC ting cannot be used for the titanium the Jiaolong. The project team also from Shanghai Customs, and a pres- alloy and this resulted in a tremendous knew that the manned cabin could sure acceptance test was done on each amount of sanding work. This was not be produced in-country. However, piece of pressurized equipment. not estimated beforehand, and thus, Russia had developed two manned it delayed the schedule of the final submersibles (Rus and Consul )and Assembly assembly. produced three titanium alloy manned Domestically produced equipment When installing brackets welded cabins, and the Russians were willing arrived in steady succession from the to the frame, we first drew hanging to produce one for China. Thus, a end of 2004. The submersible’stita- lines or, if necessary, made installation Russian institution was commissioned nium alloy frame was made in Russia templates. The parts were then sanded to produce the Jiaolong’smanned but was not delivered until November to make them match each other, cabin, and the pressure acceptance 2005. Therefore, a temporary steel weighed, and then spot welded. Rele- test was done at the Krylov Shipbuild- frame was produced locally based on vant work fixtures were installed to ing Research Institute. On January 29, the detailed design drawings for the ensure an accurate installation and 2003, COMRA signed a contract with trial installation at the end of 2004 reduce welding distortion. Later, we theRussianKrylovInstitutetopro- in order to shorten the installation inspected the assembly, and if it duce a 7,000-m manned submersible’s time. In September 2006, when all passed, we finally welded it for a fur- titanium alloy structure. the equipment and components, im- ther inspection. The buoyancy foam was originally ported or domestically produced, had Firstly,37piecesofbuoyancy planned to be procured from Russia reached CSSRC, we started the general blocks were installed externally in the but its specific weight was around assembly of the submersible’s hull, 10 sections of the titanium frame; 0.65. This would have brought bracket, equipment, outfitting, piping, 43 pieces of buoyancy blocks were in- the submersible’stotalweightupto cable, etc., into a complete submers- stalled internally (including 13 pieces 25 tons, which exceeded the techni- ible, in order to experiment a complete at the head); and then 161 brackets cally allowed limit of 22 tons. Later, integrationona1:1steelframeand which connected the buoyancy blocks an American company, Emerson & made preliminary interfaces debug- and titanium frame were welded or Cuming, Inc., was willing to supply ging tests. bolted to the titanium frame and buoyancy material, DS32, with a spe- After receiving the submersible’s bolted to the buoyancy blocks. It cific gravity of 0.525. A contract was final titanium frame at the final assem- should be noted that, when installing signed and sent to the U.S. govern- bly site, we first measured the frame’s the buoyancy blocks on the titanium ment for approval. The U.S. govern- geometric dimensions and then deter- frame, we had to ensure a fair shape ment agreed but added restrictions on mined the reference position of the of the submersible. the DS32 foam and only authorizing installation. A laser was used during Since the distortion tolerance of the Emerson to provide its DS35 foam, the installation process to monitor welded titanium frame was far more atypeofbuoyancymaterialwithaspe- any changes in the reference position. than that of the machined buoyancy cific gravity of 0.561. Unfortunately, the Russian-made blocks, the thickness of each correc- Contracts for other imported titanium frame’smountingdimen- tion gasket had to be modified several equipment were signed with foreign sions were beyond the permissible tol- times during the installation; this was firms, in most cases, following the erance, causing significant problems extremely cumbersome and heavy technical design. The imported equip- with the installation of brackets for work. ment reached Shanghai Customs in light shells and equipment brackets. If the installation of the buoy- succession from March 2005 until Because these brackets were made on ancy blocks contradicted the arrange- November 2005. However, since the basis of the drawings and thus ment of the frame or interfered with
44 Marine Technology Society Journal equipment or cables, modified lines (1) We confirmed that connections tank test to Jiaolong’sTechnicalTest would be drawn on the buoyancy were correct and reliable by repeat- Plan process to identify problems in blocks and they would be modified edly checking the cable connec- water and solve them, before going to by hand. All these buoyancy blocks tions among the equipment. sea trials. had to be hand modified on site until (2) The onshore debugging check. The open-water tank test included they dimensionally fitted the frame All the electrical circuits and signal (1) underwater system verification, and other interfaces representing a lot transmission paths were checked (2) checking the operation and inte- of added assembly work had to be with battery power. gration performances of each sub- done on the site. (3) The results of onshore debugging system and their required functions, Having installed the external buoy- were determined by the complete (3) confirming the practicability of ancy blocks and adapted them to the operating equipment checkpoints. thedesignedworkprocedureofeach required positions, welders welded The final assembly and onshore mission, (4) examining the accuracy the blocks’ brackets to the frame. combined debugging tests altogether and reliability of the exchange of in- The welding distortion of the external took 1 year and lead to the open- formation flow and control flow, and buoyancy blocks had to be considered water tank test phase that followed. (5) accumulating the relevant data. carefully, otherwise the bolts on the ex- The main tasks of the open-water ternal buoyancy blocks could not be Open-Water Tank Test tank test completed include the screwed into the nuts on the brackets. following: Our welders attempted to resolve this CSSRC has an open-water tank 1. measuring the submersible’sweight problem again and again, and then shaped like a circular basin, with a di- and center of gravity; decided to control the welding distor- ameter of 85 m and a maximum depth 2. determining drainage volume and tion by reducing the welding current of 15 m, which is equipped with an in- coordination of the center of buoy- and discontinuously welding on both door dock. This dock is 30 m × 8 m × ancy by a balancing test; sides. 8 m and has a 30-ton bridge crane 3. determining the mooring pro- The acoustic equipment such as the (shown in Figure 2). Thanks to this pulsive force and the relationship bathymetric side-scan sonar, Doppler facility, we could add an open-water between the rotation rates of each speedometer and motion sensors re- propeller; quired very high installation accuracy, FIGURE 2 4. evaluating the submersible’s ability and trial and error methods with special to regulate the trim angle, accu- Open-water tank (a) and corresponding tools were used to meet the accuracy dock (b). mulating experience by rehearsing requirement. according to “Operating Rules of The onshore combined debugging Each Post of Sea Trials (draft)” and was carried out after the final assembly. the rules of implementation com- The main purpose of the onshore com- piled for each dive in a sea trial; bined debugging was to ensure our work 5. debugging the control performance could enter the next phase, the open- of a 6 degree-of-freedom motion of water tank test, by checking whether the submersible and submersible’s the interfaces between the equipment comprehensive performance of and subsystems were accurate, whether landing on the seabed; their communications were right, and 6. debugging the submersible’s auto- whether they were able to perform matic control function; their required functions. The onshore 7. simulating the task of sampling; combined debugging was a bridge 8. debugging the interfaces between between the final assembly and the the submersible and tools; and open-water tank test; it marked a step 9. debugging the comprehensive oper- forward from equipment to system. ational capability of the submersible. The following aspects were the focus The open-water tank test lasted for of the onshore combined debugging: 110 days, from October 3, 2007 to
May/June 2013 Volume 47 Number 3 45 January 20, 2008. Underwater tests the relevant requirements. Two months State Oceanic Administration, and were performed 53 times during this later, on March 2, 2008, in Wuxi, the the organization of the sea trial was period, and 18 staff members entered State Oceanic Administration held a formally established. the manned cabin. A series of malfunc- Pre-Delivery Inspection and Confirma- The supporting ship was clearly tions were discovered during these tion meeting. It was concluded that the identified as a very important element tests, such as the malfunctions of the submersible had met all the technical for the sea trials test as well as for propellers, trim pump, high-pressure qualifications required by the sea trials’ all future utilization. However, due to air relief valve, anti-collision sonar, outline and that the Jiaolong was ready restricted project funding, it was im- hydraulic source, and seawater valves, for ocean sea trials. More detailed intro- possible to develop a specific mother- as well as the rupture of the compen- duction about open-water tank tests can ship for Jiaolong in a parallel effort, so sation film of the main and secondary be found in Hu et al. (2008) and Cui a temporary ship had to be selected battery boxes. These were all detected et al. (2009). and refitted for the sea trials test. After and corrected on site. various efforts, an older oceanographic Another task of the open-water Sea Trials survey ship, the Xiangyanghong-09, tank test was to train the pilots and op- The sea trials were the final phase was chosen (Figure 3). A series of mod- erational team for the sea trials. Several of the Jiaolong’s development but also ifications and updates were necessary staff members participated in the train- represented the greatest risk. Success such as adding an A frame at the stern ing program and dove the Jiaolong or failure of the entire project de- and modernization of the living quar- during the tank tests. This included pended on the results of these tests. ters. In the aft deck, a special platform Mr. Cong Ye, who was the chief The purpose of the sea trials was to was constructed for the storage and designer of the general arrangements comprehensively examine the techni- maintenance of the submersible. of Jiaolong. He was also a member cal performance, operation efficiency, The main technical characteristics of the team that participated in a safety and reliability of the completed of the ship are given below. Sino-U.S. joint deep diving voyage, submersible, to determine whether its Length overall: 112.05 m and he was the only member who performance met all contract require- Breadth moulded: 15.2 m obtained two chances to dive with ments, design files and relevant norms, Draft: 5.5 m Alvin. He was consequently selected to ultimately decide if it could be deliv- Displacement: 4,435 tons to be the chief pilot of the Jiaolong ered, accepted and declared in opera- Endurance: 60 days in the sea trials. At the same time, tional activity. Cruising speed: 12 km, maximum the two future professional pilots, The Jiaolong’s sea trial was a com- speed: 15 km Mr. Wentao Fu and Mr. Jialing Tang, plex system engineering process, which Deck equipment: 6,000 m electrical continued their training and would not only concerned the submersible winch for geology, 2,000 m hydraulic be given as many operational chances itself and the technical state of the winch for acoustic communication. as possible. surface support system but also in- Scientific investigation equipment: On January 17, 2008, an expert volved preparation of the sea area for Sub-bottom profiler, Acoustic Doppler panel organized by COMRA came to the trial, organizing the testing per- CSSRC to test the Jiaolong.Thetest sonnel, preparing the relevant vessels, program consisted of a wide variety preparing a contingency plan for the FIGURE 3 of functional tests which included sea trial, and many logistics factors. Xiangyanghong-09 and its main facilities. (1) displacing water from ballast tank, Our project team began to do the rel- (2) executing the automatic directional evant preparation work in 2005, in- navigation, (3) sample hovering at a cluding drawing up sea trial files, designated position, (4) operating the purchasing spare parts, refitting the life support system, and (5) jettisoning mother ship, selecting and preliminar- the solid ballast. The results of this test ily training pilots and operators, and sequence demonstrated to the satisfac- selecting the appropriate sea areas for tion of the expert panel that the submers- the trial. At the end of 2007, an outline ible’s functions and performance met of the sea trial was approved by the
46 Marine Technology Society Journal Current Profiler (ADCP), Conductiv- face VHF and underwater acoustic and the public. More detailed infor- ity, Temperature, and Depth (CTD), communication systems did not mation on the first two phases of sea Ultra-short Baseline (USBL) work. The second problem was caused trials can be found in Liu et al. (2010) Laboratories: e.g., dry lab, wet lab, by having to use expired silver-zinc and Cui et al. (2010). biology lab, submergence control cen- batteries due to funding problems. After the success of the 3,000-m- ter, network center The batteries failed in most of the level sea trial, the ministry of science Total space for crew aboard the ship: dives and this added a significant and technology directly approved the 96, including 45 ship operators, 2 med- maintenance work load on the crew. “Technical Improvement of the Jiaolong ical staff and a maximum of 49 for the Another major problem encountered Manned Submersible and 5,000– test team. during the 300-m sea trial was the 7,000 m Sea Trials.” This contract re- Figure 3 shows a picture of leakage of watertight cables and con- quired that all improvements, the 5,000– Xiangyanghong-09 and its main facil- nectors. Through the joint efforts of 7,000 m sea trial and the full classifica- ities.Themainchallengeforthetest the test team, we successfully finished tion work of the Jiaolong should be team was the ship’s lack of a dynamic the 1,000-m class test and a new Chi- done within 2 years. Classification positioning system (DPS). All station- nese record of 1,109 m was achieved. work had not been included in the keeping had to rely on the ship master’s With this hard won initial sea trials initial contract for the development. expertise to maintain safe operating dis- success, the ministry of science and Before the 5,000-m-level sea trial, tances between the supporting ship and technology approved the follow-on some comprehensive technical im- the submersible. Close tracking of the project of “Improvement of Jiaolong provements were made in five aspects, submersible’s position was critical in Manned Submersible’s Key Tech- including (1) the upgrade of the video order to maintain reliable acoustic com- niques and Research of 3,000-m- system, (2) the improvement of the munication during test dives. Otherwise, Level Sea Trial.” The new project was operation system, (3) grounding detec- we would lose sight of the submersible aimed at completely and comprehen- tion system, (4) positioning system and after surfacing at the end of a dive. sively resolving the problems revealed (5) acoustic system. These improve- The 1,000-m-level sea trials were in the 1,000-level sea trial, including ments were all focused to enhance the formally started in 2009, and this the sitting on bottom ability, conve- Jiaolong’s safety and capacity for work. proved the most difficult time in all nience and reliability of the grounding China’s contracted sea area of poly- the sea trials. Firstly, the season was detection system, reliability of the hy- metallic nodules was deliberately not appropriate as it was typhoon sea- draulic system, contacts between the chosen as the test site for the 5,000-m- son in the South China Sea. Secondly, stabilizers and the seabed, reliability level sea trials. This would simulta- problems due to the lack of experience, of the video system, reliability of the neously conduct an investigation into improper design and assembly errors control system, and the reliability of the natural resources and do scienti- occurred in almost every dive and the acoustic system. fic research in this area, as required of this continuously accrued the percep- From May 31 to July 18, 2010, the COMRA by the International Seabed tion of project risk. Thirdly, overall Jiaolong’s 3,000-m-level sea trial was Authority. This sea trial was done from support for the project was precarious performed in the South China Sea, in July 1 to August 18, 2011. Since the and the team understood that there which the Jiaolong made 17 dives and test area was far away from China, the was no route of retreat. If this initial the maximum dive depth of 3,759 m working time was just 2 weeks, because sea trial phase failed, the whole project was reached. the travel time was almost one month. would be canceled. Consequently, the All required test missions were suc- The weather conditions remained terri- only option was to solve these prob- cessfully completed in this sea trial, and ble throughout the entire sea trials. We lems on site and complete the necessary the results even exceeded our expecta- were only able to make five dives with sea trial objectives. A brief summary tions, especially since the submersible depths of 4,027 m, 5,057 m, 5,188 m, for all the test dives of Jiaolong sub- had run without any anomaly in the 5,184 m, and 5,180 m, respectively. mersible is given in Table 3. last two dives. The ministry of science Apart from the first dive, each of the In the 1,000-m class tests, the most and technology saw a great possibility other four dives successfully landed challenging technical problem was the of success from this sea trial, and the re- the submersible on the seabed several communication system. Both the sur- search project was opened to the media times and all systems functioned well.
May/June 2013 Volume 47 Number 3 47 TABLE 3
Dive log of Jiaolong sea trials.
Dive No. Date Test Site Depth (m) Brief Description
1 2009.8.3 Dock 1 2.4 Carried out the launch and recovery exercise with no persons in the cabin. 2 2009.8.3 Dock 1 2.4 Carried out the launch and recovery exercise with persons in the cabin. Carried out the ground detection. 3 2009.8.4 Dock 1 2.4 Finished the launch and recovery test and the grounding detection. 4 2009.8.15 Dock 2 2.4 Finished the launch and recovery test and the check of submersible functions; Finished the grounding detection. 5 2009.8.15 Dock 2 2.4 Finished the launch and recovery test. Debugging the VHF system and acoustic communication system. 6 2009.8.16 A1 2.4 Finished the VHF communication test but the acoustic communication system did not work. 7 2009.8.17 A1 2.4 Carried out the functional test for the main ballast system and due to high positive buoyancy, the submersible did not dive. 8 2009.8.18 A1 38 Finished the diving test by thrusters. 9 2009.8.20 A1 2.4 Finished the test of the acoustic communication system with the main engines of the mothership stopped or operated. 10 2009.8.21 A1 41 Finished the functional test of filling and draining of the main ballast water tank; Finished the check of navigational functions; Finished functional test for the variable ballast system and the trim adjustment system. 11 2009.8.23 A1 44 Finished the releasing test of the emergency buoy. 12 2009.8.30 B1 2.4 Debugging of the acoustic communication system. 13 2009.8.31 B1 213 Balance test in 200-m depth; Debugging the acoustic communication system. 14 2009.9.7 B1 100 Established the Morse code communication. Test terminated due to severe weather. 15 2009.9.12 Dock 2 2.4 Finished grounding detection; Debugging the acoustic communication system. 16 2009.9.13 B1 335 Finished the functional check for manual navigation with and without computer. Finished functional test for automatic orientation, depth, height and hovering; Finished the functional test for trim adjustment; Finished the functional test for the variable ballast system; Finished sitting on bottom. 17 2009.9.18 B1 268 Finished functional test for automatic orientation, depth, height and hovering; Finished the test for payload; Finished the functional test for side scan sonars and hydrothermal samplers; Finished the functional check for manual navigation without computer. 18 2009.9.20 B1 292 Finished sitting on bottom and placing markers; Finished functional test of the acoustic communication system; Testing the automatic height function. 19 2009.9.30 Dock 2 2.4 Finished grounding detection and functional test for the variable ballast system; Debugging the acoustic communication system. 20 2009.10.3 C2 1,109 Finished un-powered diving and floating; Finished the whole process of submersible diving operation. 21 2010.5.29 Dock 1 2.4 Finished the launch and recovery training for the operators; Finished the functional check for the ground inspection system. 22 2010.6.8 A1 2.4 Submersible turning when launched in water and one towing rope cut the cable of one transducer. Fortunately the transducer was saved by the persons in the rubber boat. Underwater filming test terminated. continued
48 Marine Technology Society Journal TABLE 3
Continued
Dive No. Date Test Site Depth (m) Brief Description
23 2010.6.9 A1 37 Finished the balance test; Finished underwater filming by a diver; Finished functional check for side scan sonars, the acoustic communication system; Finished navigational function check. 24 2010.6.11 B1 291 Finished solid blast weight check in 300-m depth; Finished the navigational function check; Finished the functional test for automatic depth, orientation and height; Finished the functional check for the acoustic communication system; Finished sitting on bottom. 25 2010.6.12 B1 291 Finished the navigational function check; Finished the functional test for automatic depth; Finished sitting on bottom; Finished operational exercise for one pilot-in-training. 26 2010.6.20 D2 2,068 Finished un-powered diving and floating; Finished solid blast weight check in 2,000-m depth; Finished the functional check for the acoustic communication system. 27 2010.6.22 D2 3,039 Finished un-powered diving and floating; Finished functional test for the acoustic communication system; Finished the functional check for the ground inspection system. 28 2010.6.27 D2 2.4 Diving test terminated when the leakage alarm of the backup battery box was sounding. 29 2010.6.28 D2 2,104 Finished un-powered diving and floating; Finished functional check for the ground inspection system; Finished operational exercise for one pilot-in-training. 30 2010.6.29 B1 286 Finished bathymetric bottom mapping with two side-scan sonars; Finished navigational function check; Finished sitting on bottom and placing the marker; Carried out target search exercise. 31 2010.6.30 B1 286 Finished the search of the marker placed in the previous dive; Finished sitting on bottom and placing the new marker; Finished operational skill test for two pilots-in-training. 32 2010.7.6 A1 33 Finished video recording and photo taking of the whole sea trial scene by the helicopter; Finished functional check for ground inspection system and the updated video system of the submersible. 33 2010.7.8 D2 2,088 Diving terminated due to the high short-circuit current value displayed by the ground inspection system; Finished functional test for the hydraulic system. 34 2010.7.9 D2 3,757 Finished un-powered diving and floating; Finished sitting on bottom 5 times; Operated the hydrothermal sampler but without obtaining water samples. 35 2010.7.11 D2 1,134 Diving test terminated when the leakage alarm of the backup battery box was sounding. 36 2010.7.12 D2 3,757 Finished un-powered diving and floating; Finished sitting on bottom, taking hydrothermal samples and placing markers. 37 2010.7.13 D2 3,759 Finished un-powered diving and floating; Finished sitting on bottom and taking samples; Finished bathymetric bottom mapping with two side-scan sonars. Finished operational skill test for two pilots-in-training. 38 2011.6.28 Dock 1 2.4 Finished launch and recovery training for the operators; Finished functional check for the ground inspection system. 39 2011.6.29 Dock 1 2.4 Finished launch and recovery training for the operators; Finished functional check for the ground inspection system. 40 2011.7.20 E3 4,027 Finished un-powered diving and floating; Finished solid blast weight check in 4,000-m depth; Finished functional check for ultra-short baseline and ground inspection system; Finished submersible functional check. continued
May/June 2013 Volume 47 Number 3 49 TABLE 3
Continued
Dive No. Date Test Site Depth (m) Brief Description
41 2011.7.25 E3 5,057 Finished un-powered diving and floating; Finished solid blast weight check in 5,000-m depth; Finished functional check for ultra-short baseline; Finished submersible functional check; Finished sitting on bottom and taking videos and photos. 42 2011.7.27 E2 5,188 Finished unpowered diving and floating; Finished navigational function check in 5,000-m depth; Finished sitting on bottom and taking videos and photos; Finished bathymetric bottom mapping of 3 km with two side-scan sonars. 43 2011.7.29 E1 5,184 Finished un-powered diving and floating; Finished navigational function check in 5,000-m depth; Finished sitting on bottom, placing markers; Finished sampling of manganese nodules and biologies; Recorded many videos and photos. Finished the whole process of submersible diving operation. 44 2011.7.31 E1 5,180 Finished un-powered diving and floating; Finished functional check in 5,000-m depth; Finished sitting on bottom, placing markers; Finished biological sampling; Recorded many videos and photos. Finished the whole process of submersible diving operation. 45 2012.6.1 Dock 1 2.4 Finished launch and recovery training for the operators. 46 2012.6.15 G1 6,671 Finished un-powered diving and floating; Finished functional check in 5,000 m and 6,000-m depths; Obtained 405 ml water sample in normal pressure and 430 ml water sample in high pressure of 28 MPa. 47 2012.6.19 G1 6,965 Finished unpowered diving and floating; Finished functional check in 6,000-m depth; Finished sitting on bottom, placing markers, micro topography survey by side-scan sonar; Obtained a sediment sample of 14 cm length; Obtained 435 ml water sample in normal pressure; Finished the whole process of submersible diving operation. 48 2012.6.22 G1 6,963 Finished un-powered diving and floating; Finished functional check and safety verification in 6,000-m depth; Finished sitting on bottom, placing markers; Obtained three sediment samples whose lengths are 21 cm, 16 cm and 18 cm, respectively; Obtained 400 ml and 435 ml water samples in normal pressure and 123 ml water sample in high pressure of 15 MPa; Caught one white sea cucumber and two pieces of nodular mineral samples. Finished the whole process of submersible diving operation. 49 2012.6.24 G1 7,020 Finished un-powered diving and floating; Finished functional check in 7,000-m depth; Finished sitting on bottom, placing markers; Finished submersible tele-communication test with the person in Beijing office; Obtained 440 ml and 445 ml water samples in normal pressure and 345 ml water sample in high pressure of 35 MPa; Finished the whole process of submersible diving operation. 50 2012.6.27 G1 7,062 Finished unpowered diving and floating; Finished functional check and safety verification in 7,000-m depth; Finished sitting on bottom, placing markers; Obtained two sediment samples whose lengths are 21 cm and 27 cm, respectively; Obtained 440 ml and 435 ml water samples in normal pressure; Caught one white sea cucumber. Carried out the biological trapping experiment with bait. Finished the whole process of submersible diving operation. 51 2012.6.30 G1 7,035 Finished unpowered diving and floating; Finished submersible functional check and safety verification in 7,000-m depth; Finished sitting on bottom and sample taking exercise; Finished functional verification of two domestic propellers by long distance cruise. Finished the whole process of submersible diving operation. Note: Dock 1 = The Jiangyin International Container Terminal; Dock 2 = The mooring site near Sanya; A1 = South China Sea (109°09′E, 18°01′N); B1 = South China Sea (112°36′E, 19°01′N); C2 = South China Sea (110°26.8′E, 17°28.45′); D2 = South China Sea (116°28′E, 18°36′N); E1 = China poly metallic nodules contract area in the northeast Pacific (154°12′W, 10°08′N); E2 = China poly metallic nodules contract area in the northeast Pacific (154°11′W, 8°40′N); E3 = The northeast Pacific (151°7′W, 4°48′N); G1 = The exclusive economic zone (EEZ) of the Federated States of Micronesia in the southern Mariana Trench (141°58′E, 10°59′N).
50 Marine Technology Society Journal Furthermore, each dive completed its been reported in several references (Cui et al., 2008a, 2008b, 2009; Liu et al., 2008), mission, including reaching the position some of them changed during the technical improvements made in the sea trials with the required depth, and no invalid period. The latest technical specifications of the Jiaolong are as follows: dives occurred as in the previous two Maximum operational depth: 7,000 m years (Table 3). This indicated that the Main dimensions: 8.4 × 4.2 × 3.4 m improved submersible’s technical state Inner diameter of manned cabin: 2.1 m was stable, our test team had matured, Weight in air: 22 tons and the sea trial’s plan and content Crew: 1 pilot, 2 scientists proved to be reasonable and scientific. Power supply: Silver-zinc battery, >110 kWh As a difference from the previous trials, Control mode: Automatic fixed height, fixed direction, fixed this sea trial was completely open to the depth, hovering and manual operations media, and several dives were broadcast Navigation system: Ultra-short baseline system, long baseline live on CCTV. A detailed introduction system motion sensors + acoustic Doppler to the 5,000-m depth class test can be speedometer found in Cui et al. (2011a, 2011b). Operation: Two seven-function hydraulic manipulator The final 7,000-m depth class test arms was carried out from June 3 to July 16, Lighting and video system: HD video camera system, LED lights 2012. Although it faced the unique Communication: Underwater acoustic communication, challenges of 7,000 m sea trials, the underwater acoustic telephone, VHF team was now fully prepared, carried communication + GPS positioning out very careful operations at sea, and Figure 4 is a photo of the latest ability to sample hovering at an accu- couldanalyzeandsolvealltheprob- design. Although the Jiaolong is the rate position are almost equivalent. Their lems that occurred on-site. After very deepest and latest manned submersible respective underwater working time strict inspection by the on-site accep- within the second generation of three- on the bottom are within the limit of tance group of experts, it was concluded crew operational submersibles, it can- manned submersibles. The Jiaolong also that the test team completed the 7,000 m not be claimed to represent the latest possesses similar performances in the sea trials safely and successfully. The state-of-the-art technology for deep aspects of automatic drive, underwater details are reported in Cui et al. (2013). manned submersibles. acoustic communication, capabilities of The sea trials tests showed that all the When comparing our Jiaolong with navigation and positioning. design requirements were fully real- the U.S.’snewAlvin (http://www. On the other hand, based on a great ized. This 7,000-m sea trials test is whoi.edu/alvin/), it can be found that, deal of operational experience, the new the deepest of the same type of deep on the one hand, the inner diameters of Alvin has a more outstanding design manned submersibles in the world. their manned cabin are the same; their of viewports, in-cabin man-machine The success of the Jiaolong submersible payload, battery power, lighting and interface, data acquisition and instru- demonstrates that China’smanned imaging systems, maneuverability and ment interfaces. submersible technology has entered The future technical trends of the club of the countries of the highest FIGURE 4 manned submersibles mainly focus on international standard. the aspects of economy, comfort and en- Jiaolong deep manned submersible. vironmental protection (Cui et al., 2011a, 2011b). Two requirements will bring Latest Technical revolutionary changes to the design of fi manned submersibles. One is to signif- Speci cations of the Jiaolong icantly reduce the running costs, mak- and Future Development ing manned submersibles comparable Trends for Deep Manned with unmanned submersibles in this Submersibles aspect (Hawkes, 2009). The other is Although the technical specifica- to miniaturize the in-cabin facilities, tions of the Jiaolong submersible have making a more comfortable in-cabin
May/June 2013 Volume 47 Number 3 51 environment (Taylor & Lawson, 2009). deep manned submersible from a histor- (Project No. 2011AA09A101). The Concerning environmental protection, ical point of view, including the design, State Oceanic Administration (SOA) this mainly relies on elimination of mer- realization of components, assembly, is the organization department of the cury as the substance to adjust the trim, open-water tank test and sea trials. sea trials of Jiaolong. China Ocean or modify the substance used in the emer- The main technical challenges met at Mineral Resources R&D Association gency jettison system. Solid ballast iron each stage are brieflyexplained,supple- (COMRA) of SOA is specifically would not be used, or only if necessary. mented by the many references pub- responsible for organizing the sea trials. These two last requirements primar- lished during the process for interested In total, 96 members from 18 domestic ily depend on the technique of a large- readers. The Jiaolong submersible is organizations jointly completed the sea flow high-pressure sea water pump. briefly compared with the new Alvin, trial tests. The author of this paper is The new Alvin’s design team once con- which is regarded as being the best in very grateful to all the team members. sidered making a breakthrough in this the deep sea community, and it is con- Comments, suggestions and language aspect at the very beginning of their cluded that, except for the design of the improvements from Dr. Don Walsh, design; however, they ultimately had viewports, in-cabin man-machine inter- Dr. Kurt Uetz, Dr. William Kohnen to give up this idea due to tremendous face, data acquisition and instrument and another two reviewers to this paper technical difficulties and lack of funds. interfaces, most of the performances are greatly appreciated. My M.Sc. Inspiteoftheirfailuretomakesuch and functions are equivalent in addition student, Mr. Hao Li did some trans- a breakthrough, it ought to have at- to the Jiaolong’s ability to dive 500-m lation for this paper and his help is tracted sufficient attention as a direction deeper. This indicates that the Jiaolong also appreciated. The work reported of technical development. Another im- can also be regarded as one of the most in this paper was completed in my for- provement direction of great potential advanced deep manned submersibles mer organization China Ship Scientific importance is the manipulator. Current for scientific operations. The 7,000-m Research Center, and now this author seven function manipulators obtained depth capability is the deepest of the has been moved to Shanghai Ocean commercially are far away from the ca- same type of deep manned submersibles University. pabilities of human hands and discov- in the world. The success of the Jiaolong ering how to develop a manipulator submersible demonstrates that China’s simulating the human hand would manned submersible technology has Author: bring a revolutionary change to the sub- entered the realm of countries with the Weicheng Cui mersible community. At the same time, highest international standard. Finally, China Ship Scientific Research Center, another direction of great interest to future technical trends of manned sub- Jiangsu, 214082, China human beings is challenging the full mersibles were also discussed. Currently with Hadal Science and ocean depth, which needs a break- Technology Research Center, Shanghai through in improving submersibles’ Ocean University, Shanghai, China speed of descending and ascending. Acknowledgments Email: [email protected] In this direction, James Cameron com- The development of the Jiaolong pleted his record-breaking Mariana submersible was sponsored by the Trench dive in March 26, 2012, with Ministry of Science and Technology References his Solo sub Deepsea Challenger (http:// under the contracts of Development Barry, J.P., & Hashimoto, J. 2009. Revisiting Kaiko deepseachallenge.com/). Another two of a 7,000-m Deep Manned Submers- the Challenger Deep using the ROV . Mar Technol Soc J. 43(5):77-8. full ocean depth manned submersibles ible (Project No. 2002AA401000); are under development (http://www. 1,000-m Depth Class Sea Trials of China Classification Society. 1996. Classifi- doermarine.com/; http://deepflight. Jiaolong Submersible (Project No. cation and Construction Rules for Diving com/). 2009AA093201); Key Technology Systems and Submersibles [S]. Beijing: People’s Improvements and 3,000-m Depth Transportation Press (in Chinese). Jiaolong Class Sea Trials of Submers- China Classification Society. 2011. Principles Summary and Conclusions ible (Project No. 2010AA094001); for plan approval and inspection of deep-sea This paper is the first one describing Operational Technology Improve- manned submersible. A supplement to the development process of the Jiaolong ment and 5,000–7,000 m Sea Trials CCS1996, Internal document (in Chinese).
52 Marine Technology Society Journal Committee on Evolution of the National Cui, W.C., Xu, Q.N., Liu, F., Hu, Z., Wang, deep manned submersible “Harmony.” In: Oceanographic Research Fleet. 2009. Science X.H., & Zhu, M. 2009. Design, construc- Paper presented in International Conference at Sea: Meeting Future Oceanographic Goals tion and open water tank test of the deep of INMARTECH2008, All Seasons Hotel, with a Robust Academic Research Fleet, Na- manned submersible “Harmony.” In: Keynote Toulon, France, October 8–10, 2008. Toulon: tional Research Council, ISBN: 0-309-14558-9, paper presented in the Sixth International Ifremer. 120 pages, The National Academies Press. This Symposium on Underwater Technology Liu, F., Cui, W.C., & Li, X.Y. 2010. China’s free PDF was downloaded from http://www. UT2009, Wuxi, China, April 2009. Wuxi: first deep manned submersible. Jiaolong. Science nap.edu/catalog/12775.html. China Ship Scientific Research Center. China—Earth Sci. 53(10):1407-10. http:// Committee on Future Needs in Deep Cui, W.C., Xu, Q.N., Liu, T., Hu, Z., Yang, dx.doi.org/10.1007/s11430-010-4100-2. Submergence Science. 2004. Future Needs in Y.N., Hu, Y., & Ma, L. 2008b. Design and Li, X.Y., & Cui, W.C. 2004. Contact finite Deep Submergence Science: Occupied and construction of the deep manned submersible element analysis of a spherical hull in the deep Unoccupied Vehicles in Basic Ocean Research, “Harmony.” J Ship Sci Technol. 30(1):17-25 manned submersible. J Ship Mech. 8(6):85-94. National Research Council, ISBN: 0-309- (in Chinese). 52917-4, 152 pages, The National Academies Li, X.Y., Cui, W.C., & Zhang, W.M. 2006. Fletcher, B., Bowen, A., Yoerger, D.R., & Press. This PDF is available from the National Fatigue life reliability analysis of titanium Whitcomb, L.L. 2009. Journey to the Academies Press at: http://www.nap.edu/ manned spherical shell. J Ship Mech. Challenger Deep: 50 years later with the catalog/10854.html. 10(2):82-6 (in Chinese). Nereus hybrid remotely operated vehicle. Cui, W.C., Hu, Z., Ye, C., & Pan, B.B. 2011a. Mar Technol Soc J. 43(5):65-76. http:// Li, X.Y., Liu, T., Huang, X.P., & Cui, W.C. Current status and future trends for deep dx.doi.org/10.4031/MTSJ.43.5.26. 2004. Determination of fatigue load spectrum manned submersibles. J Cent South Univ T. for pressure hull of a deep manned submers- 42(Suppl. 2):13-20 (in Chinese). Forman, W. 2009. From Beebe and Barton ible. J Ship Mech. 8(1):59-70 (in Chinese). to Piccard and Trieste. Mar Technol Soc J. Cui, W.C., Hu, Z., Ye, C., & Xu, Q.N. 43(5):27-36. http://dx.doi.org/10.4031/ Lu, B., Liu, T., & Cui, W.C. 2004. Ultimate 2010. First two phases of sea trials of deep MTSJ.43.5.14. strength of pressure spherical hull in deep-sea manned submersible “Jiaolong.” In: Ocean manned submersibles. J Ship Mech. 8(1): Innovation Conference (OI2010), October Hawkes, G. 2009. The old arguments of 51-8 (in Chinese). 17-20, 2010. St. John’s, Canada: The Marine manned versus unmanned systems are about Ma, L., & Cui, W.C. 2004. Simulation of Institute of Memorial University, Marketing to become irrelevant: New technologies are dive motion of a deep manned submersible. & Business Development Division. game changers. Mar Technol Soc J. 43(5): 164-8. http://dx.doi.org/10.4031/MTSJ. J Ship Mech. 8(3):31-8. Cui, W.C., Liu, F., Hu, Z., Zhu, M., Guo, W., 43.5.21. Ma, L., & Cui, W.C. 2005. Path following & Liu, C.G. 2013. On 7000 m sea trials of control of a deep-sea manned submersible the manned submersible “JIAOLONG.” Mar Hu, Z., Wang, X.H., Zhu, M., Xu, Q.N., based upon NTSM. China Ocean Eng. Technol Soc J. 47(1):67-82. http://dx.doi.org/ & Cui, W.C. 2008. Tank test of the deep “ ” 19(4):625-36. 10.4031/MTSJ.47.1.2. manned submersible Harmony [C]//. In: the fi 3rd Asian-and Paci c Diving and Underwater Ma, L., & Cui, W.C. 2006a. Heading control Cui, W.C., Liu, F., Hu, Z., Zhu, M., Guo, W., – Technology Conference, Shanghai, June 13 15, study of a deep manned submersible at a low & Wang, C.S. 2011b. 5000 m sea trials test of 2008. Shanghai: Shanghai Society of Naval speed and large drift angles based on fuzzy the deep manned submersible “JIAOLONG.” Architects and Marine Engineers. sliding mode control. Ocean Eng. 24(3):74-8 Shipbuilding of China. 52(3)(Serial No. 197): (in Chinese). 1-14 (in Chinese). Jarry, J. 1986. SAR, NAUTILE, SAGA, ELIT-four new vehicles for underwater work Ma, L., & Cui, W.C. 2006b. Dynamic Cui, W.C., Liu, Z.Y., & Xu, Q.N. 2008a. The and exploration: The IFREMER approach. system identification of manned submersible four-element method for the design of large IEEE J Oceanic Eng. OE-11(3):413-7. http:// in horizontal plane. Shipbuilding of China. complex engineering system. Shipbuilding of dx.doi.org/10.1109/JOE.1986.1145192. 47(2):76-81 (in Chinese). China. 49(2)(Serial No. 181):1-12 (in Chinese). Kohnen, W. 2009. Human exploration of Momma, H. 1999. Deep ocean technology at Cui, W.C., & Ma, L. 2009. Hydrodynamic the deep seas: Fifty years and the inspiration JAMSTEC. Mar Technol Soc J. 33(4):49-64. problems involved in submersible design. continues. Mar Technol Soc J. 43(5):42-62. http://dx.doi.org/10.4031/MTSJ.33.4.6. In: Proceedings of the 9th National http://dx.doi.org/10.4031/MTSJ.43.5.30. Congress on Hydrodynamics and 22nd Nanba, N., Morihana, H., Nakamura, E., & National Conference on Hydrodynamics, Liu, F., Cui, W.C., & Li, X.Y. 2008. Watanabe, N. 1990. Development of deep 9-29 (in Chinese). Beijing: Ocean Press. Introduction to design and construction of submergence research vehicle “SHINKAI
May/June 2013 Volume 47 Number 3 53 6500.” Technical Review of Mitsubishi Heavy Russian Maritime Register of Shipping. Industries, Ltd. 27(3):157-68. 2004. Rules for the Classification and Construction of Manned Submersibles, Ship’s Naval Sea Systems Command (NSSC). Diving Systems and Passenger Submersibles [S]. 1998. System Certification Procedures and Moscow: RS Press. Criteria Manual for Deep Submergence Systems. Revision A, SS800-AG-MAN-010/ Sagalevitch, A. 2009. From the bathyscaph P-9290. Published by Direction of Commander, Trieste to the submersibles Mir. Mar Technol Naval Sea Systems Command, 0910-LP- Soc J. 43(5):79-86. http://dx.doi.org/10.4031/ 018-2840. MTSJ.43.5.3.
Pan, B.B., & Cui, W.C. 2010. An overview Taylor, L., & Lawson, T. 2009. Project of buckling and ultimate strength of spher- Deepsearch: An innovative solution for ical pressure hull under external pressure. accessing the oceans. Mar Technol Soc J. Mar Struct. 23(3):227-40. http://dx.doi.org/ 43(5):169-77. http://dx.doi.org/10.4031/ 10.1016/j.marstruc.2010.07.005. MTSJ.43.5.28.
Pan, B.B., & Cui, W.C. 2011. A comparison Takagawa, T., Momma, H., & Hotta, H. of different rules for the spherical pressure hull 1995. Advanced technology used in Shinkai of deep manned submersibles. J Ship Mech. 6500 and full ocean depth ROV Kaiko. 15(3):276-85. Mar Technol Soc J. 29(3):15-25.
Pan, B.B., & Cui, W.C. 2011. On an appro- priate design and test standard for spherical pressure hull in a deep manned submersible. In: Proceeding of 2011 IEEE Symposium on Underwater Technology (UT 2011) and 2011 Workshop on Scientific Use of Submarine Cables and Related Technologies (SSC 2011), Tokyo, Japan, 5-8 April 2011, IEEE Catalog Number: CFP11UTS-PRT, ISBN: 978-1- 4577-0165-8, pp. 436-442. Tokyo: Institute of Industrial Science, University of Tokyo
Pan, B.B., & Cui, W.C. 2012. Structural optimization for a spherical pressure hull of a deep manned submersible based on an appropriate design standard. IEEE J Oceanic Eng. 37(3):564-71. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier. 10.1109/JOE.2012. 2190809.
Pan, B.B., Cui, W.C., Shen, Y.S., & Liu, T. 2010. Further study on the ultimate strength analysis of spherical pressure hulls. Mar Struct. 23(4):444-61. http://dx.doi.org/ 10.1016/j.marstruc.2010.11.001.
Rona, P.A. 2000. Deep diving manned research submersibles. Mar Technol Soc J. 33(4):13-25. http://dx.doi.org/10.4031/ MTSJ.33.4.3.
54 Marine Technology Society Journal PAPER Reliability-Centered Development of Deep Water ROV ROSUB 6000
AUTHORS ABSTRACT Vedachalam Narayanaswamy This paper presents the reliability-centered development of a deep water Ramesh Raju Remotely Operable Vehicle (ROV) ROSUB 6000 by the National Institute of Ocean Muthukumaran Durairaj Technology (NIOT), India. ROV operations are required during deep water interven- Aarthi Ananthapadmanabhan tions, such as well head operations, emergency response situations, bathymetric Subramanian Annamalai surveys, gas hydrate surveys, poly-metallic nodule exploration, and salvage oper- Gidugu Ananada Ramadass ations. As per our requirements, the system needs to be capable of deep water Malayath Aravindakshan Atmanand operation for a period of 300 h/year and to be extremely reliable. Methodologies National Institute of Ocean applied during the development and enhancement phases of electrical and control Technology, Chennai, India systems, taking into consideration the cost, space, and time constraints to attain the best possible reliability are detailed. Reliability, availability, and maintainability (RAM) studies are carried out to identify possible failure cases. It is found that Introduction ROV-Tether Management System (TMS) docking failure could be detrimental to he remotely operable submersible the ROV system, and manipulator system failure could be detrimental to subsea ROSUB 6000 for deep sea operation is operations. It has been calculated and found that the improved design has a T mean time between failure (MTBF) of 4.9 and 6.2 years for ROV-TMS docking an electric work class Remotely Oper- able Vehicle (ROV), equipped with and manipulator system operations, respectively. The importance of monitoring two manipulators and having an addi- tether cable healthiness during normal and winding operations and the systems im- tional pay load capability of 150 kg plemented for effectively monitoring and maintaining the tether cable operational for mounting scientific and mission- and functional healthiness, using the tether cable pay-out, vehicle heading, electric oriented subsystems. The ROSUB sys- insulation, and optical performance sensors with the aid of a sea battery, are dis- tem comprises the main components, cussed. Maintenance decision support tables, which detail the operational person- namely the ROV, Tether Manage- nel for the upkeep of the systems during the indicated interval so that the highest ment System (TMS), Launching and possible reliability is maintained during the mission period, are also presented. Recovery System (LARS), ship sys- Keywords: remotely operated vehicle, reliability, probability of failure, mean time tems, control console, instrumenta- between failure, FMECA analysis tion, control and electrical system, Hydro Acoustic Navigation System (HANS), and the control and opera- The umbilical is an electro-optic in- from the launching vessel. Manipu- tional system (Manecius et al., 2010; terface between the TMS and the ship lators mounted on the ROV are used Ramesh et al., 2010). Figure 1 shows and is used to carry the weight of the to carry out the required subsea opera- the overall view of the ROV with TMS and the ROV. tion. After completion of the task, the LARS in the ship. The LARS takes the ROV-TMS ROV is docked back to the TMS in the Figure 2 shows the system launch- docked system below the splash zone subsea location, and the system is taken ing phase, where the work class ROV and undocks it. The ROV-TMS sys- back to the ship. and the TMS are docked together and tem is lowered to the location of inter- Figure 3 indicates the electrical and launched from the mother vessel using est. As the docked system gets closer control system architecture in the TMS, the LARS. The storage winch houses to the target of interest, the ROV is ROV, and the ship. The ship power the 7,000-m-long umbilical cable, released from the TMS. The ROV is at 415 V at 50 Hz is converted into and its operation is synchronized equipped with thrusters and can be 6,600 V at 460 Hz, using a combina- with the LARS and other deck gear. operated on the pilot’scommand tion of a standard frequency converter
May/June 2013 Volume 47 Number 3 55 FIGURE 1 in the TMS and the ROV convert power at 6,600 V at 460 Hz to the View of the system architecture of ROSUB 6000. power level requirements of the sub- systems. The voltage of 6,600 V is selected as a tradeoff between the size of the umbilical/tether cables, while the voltage drop is managed in the 6,000 m transmission cable and the powerrequirementsofthesystem.A frequency of 460 Hz is used to reduce thesizeandweightofthemagnetic components in the ROV and TMS. Electronic controllers with input- output modules are used for interfac- ing with the field devices in the TMS and the ROV. Data formats are man- aged by using multiplexers and media converters. The ROV and TMS systems communicate with the ship system using the fiber optic Ethernet link through the slip rings located in the TMS and deck storage winches. The manipulators can be operated from the control console, and the control is interfaced to the ROV and the ship side controllers at either end. and a step-up transformer. The electro- Ramesh et al., 2010), while the con- optical connectivity between the ship nectivity between the TMS and the RAM Methodology and andtheTMSisachievedbya7,000-m ROV is obtained by a 400-m-long the Standards Followed umbilical cable (Manecius et al., 2010; tether cable. Subsea power converters As the ROSUB 6000 system is to be involved in mission critical applications, FIGURE 2 reliability, availability, and maintainabil- ity (RAM) are of utmost importance. As View of the ROSUB 6000 system ready to be launched. part of the RAM studies, Failure Mode Effects Analysis (FMECA) studies were done to identify the possible failures. Failures were classified into four categories based on their impact on the overall system, and the most critical failure surfacing in each category is taken up for improvements. a. Type 1 failures that have a minimal impact on the mission objective and the system, e.g., failure of one of the lamps or cameras in the ROV. b. Type 2 failures that could defeat the mission objective, but not damaging
56 Marine Technology Society Journal FIGURE 3 The following are the list of the major standards followed: Electrical and control architecture of the ROSUB 6000 system. 1. FIDES Guide for Reliability Meth- odology (FIDES Guide, 2009) for electronic systems, which deals with the mission and environment spe- cific analysis. 2. MIL HDBK 217F Military Hand- book for Reliability Estimation (U.S. Department of Defense, 1991) of the Electronics Equipment. 3. OREDA Handbook (OREDA AUTOR, 2003) for Offshore Reliability Data. 4. IEEE 493 IEEE Recommended Practices (IEEE Standard, 1997) for the Design of Reliable Industrial and Commercial Power Systems. 5. Reliability of Valve Regulated Lead Acid Batteries (DeAnda et al., 2004), a study by the U.S. Department of Energy, Energy Storage Systems program. Failure rate determination is done by the following methods: a. Based on the manufacturer’sdata and interpretation suitable for the mission profile. b. For systems and circuit boards, where schematics are available, using component failure data from the respective standards, and calcu- lating the failure rates taking the mission profile, operating condi- tions and stresses into consideration. c. For commercially sourced circuit boards, where there is no adequate to the systems involved, e.g., failure 1. Failure of the ROV to dock with information, based on the functional of the subsea positioning system. the TMS underwater. specification, the failure rate for the c. Type 3 failures that cause damage to 2. Failure of the manipulator when mission profile is calculated using the system itself, e.g., ROV-TMS carrying out a subsea task. standards. docking failure. Reliability trees are drawn to find out the The FIDES approach is based on d. Type 4 failures that could cause probability of failure for the identified two physics and the failures supported by damage to the system as well as critical operations. Calculations were per- the analysis of test data, feedback the subsea installation, e.g., manip- formed to find out the mean time be- from operations and existing models, ulator failure while in operation. tween failure (MTBF) for a 5-year period, along with the statistical interpreta- The following Types 3 and 4 fail- with the system clocking deep water tions over the normal operating life ures are described in this paper: operation for a period of 300 h/year. period of the involved systems.
May/June 2013 Volume 47 Number 3 57 The standard considers the in- motor power electronic controller. region and then recovered to the deck. fluence of the operating temperature, It can be seen that the device has a fail- Figure 4 shows the pilot view of the amplitude and frequency of the tem- ure rate of 77 and 446 FIT for a mis- ROV-TMS docking, captured by the perature changes, vibration amplitude, sion profile of 300 and 8,760 h/year, illuminated camera located in the TMS humidity and operating stress factors. respectively. during ROV deep water operations in For example, the impact on the life- The failure rates of the components 2008, where the navigation parameters time due to the operating temperature, are calculated at the circuit component are displayed on the pilot screen in the thermal cycling and vibration stresses level and incorporated in the reliabil- ship’s control console. are based on the Arrhenius, Norris ity trees. Table 2 gives the standards The camera and lights located in and Basquin laws (FIDES, 2009). followed for the major systems and the TMS will aid the pilot in carrying The standards make provision to ac- components. out the ROV-TMS docking. Given count for manufacturing and integrating The TOTAL-SATODEV’sGRIF below is the process sequence in carry- quality factors into the calculations, software is used for realizing the trees ing out a successful subsea docking taking into account the environmental for calculating the probability of failure process. conditions and stresses during differ- for a specific time period, with provi- a. Pilot the ROV close to the TMS ent mission profiles. The standard sions to incorporate the mean time to re- location. also provides the commercial off-the- pair (MTTR), and the options to select b. Wind the already released tether shelf approach for calculating the fail- the reliability laws based on the avail- cable back in the TMS by operat- ure rates of commercially available ability of field failure data. In this ing the winch in the TMS. circuit boards for the defined mission study, exponential laws are applied, as c. Pilot the ROV vertically down the profile with the functional require- the field failure data are very limited TMS and operate the top thrust- ments and mission profile as an input for subsea and similar systems. ers to produce a downward thrust from the user. (normally ROV is upward buoyant The failure rate of the components by 20 kg) in such a way that the is not a linear function with time. Reliability and Availability tether cable is held under minimum Failure rates are usually mentioned Type 3 Failure Scenario: tension. in terms of the number of failures per ROV-TMS Docking Failure; d. With the minimum tension in the billion hours (FIDES, 2009), abbre- Normal ROV-TMS Recovery cable, operate the TMS winch and viated as failure-in-time (FIT). As When the ROV completes the wind the tether cable in a way that an example, Table 1 populates the identified mission, it has to be docked the cable is without any slack. calculated failure rate of a thruster with the TMS, and the docked system e. Continue the winding at a slower has to be brought to the subsurface pace until the ROV enters the TMS TABLE 1 close to the ship, so that the ROV- cone and gets onto the latches (which TMS system can be docked with the will be indicated by the limit switches Failure-in-time date for brushless direct current LARS in the splash-free subsurface inside the latches). (BLDC) motor power electronics controller.
Hours of Operation Failure-In-Time per Year (FIT) TABLE 2
164Major standards followed for study. 100 68 Component Standards 300 77 CPU, AC-DC converters, DC-DC converters, fuses, electronics FIDES 500 85 and optical connectors, Ethernet converters, data and video 3,000 195 multiplexers, input and output modules for data acquisition cards 5,000 282 HF converters and transformers, isolators, motors MIL and IEEE 8,000 413 Power contactors, halogen lamps MIL 8,760 446 Umbilical and tether cables, terminations, subsea sensors OREDA
58 Marine Technology Society Journal FIGURE 4
Illuminated camera view of the ROV docking to the TMS.
Docking Failure the tether cable and as it is positively a. Base design case The following failures could lead buoyant, it tends to surface. This sur- Failure trees are drawn to calcu- to docking failure: facing is detrimental to the ROV and late the probability of failure for a a. TMS docking vision support, the released tether cable, as there are 5-year period, with the system in oper- b. TMS tether winch operation, increased chances of entanglement ation in deep waters for a period of c. ROV thrusters for the docking with the ship’s systems such as thrust- 300 h/year. From the tree shown in operation, and ers. To minimize the chances, the Figure 6, it can be seen that the prob- d. Tether cable twist indication from probability of the ROV-TMS dock- ability of failure is 92.48% and the the TMS. ing failure has to be minimized to the MTBF works out to 1.9 years. The The failure in any of the above results lowest possible level. forthcoming sections detail the tech- in the ROV-TMS docking failure. The base design case indicates the nical improvements made to attain a Figure 5 shows such a condition. preliminary system design. During MTBF of 5 years. In such a scenario, the ROV has the operational phases, based on the b. Maintaining spares for ship-based to be salvaged after bringing it to the experience acquired, the systems are electric systems water surface. This is done by winding improved. The improvements are The failure trees are analyzed for the deck umbilical cable, until the incorporated in the base case, and the contribution made by the deck- fi TMS surfaces and is docked with the their bene ts in terms of the MTBF based systems. It is calculated that fail- LARS. As the ROV is linked with are detailed. ure probability of 6 kV power supply input to the TMS is 64.65%. This power supply input is used by all the FIGURE 5 systems in the TMS and ROV. It is View indicating system recovery after a docking failure. found that the following components which have higher failure rates are reparable within 10 h by having a hot standby on board the deployment vessel: a. High-frequency (HF) converter b. Umbilical storage winch slip ring c. Medium-voltage (MV) transformer d. Isolators e. Ship-side data multiplexer
May/June 2013 Volume 47 Number 3 59 FIGURE 6
Tree for calculating the docking failure MTBF for the base design case.
f. Real-time controller b. Cable winding counter to ensure industrial standard vacuum circuit g. Photonic inertial navigation system that the already released cable is breaker (VCB) is not an attractive solu- h. BLDC motor controller wound back. tion as a typical VCB of minimum rat- By means of having spares in the The black-dock sensors enable the ing of 400 A at 7.2 kV weighs around ship, the probability of failure of the pilot to carry out the docking opera- 25 kg and has a dimension of ap- power supply input to the TMS can tion in the event of vision system fail- proximately 0.4 m (L) × 0.21 m (W) × be reduced from 64.65% to 1.38%. ure. From the failure trees in Figure 7, 0.32 m (H). In addition to their huge Hence, the MTBF can be increased it can be seen that, by using the black- footprints, such circuit breakers should to 3.3 years. dock system, the probability of failure be operated inside pressure-rated en- c. By introducing black-dock sensors is reduced to 16.71% from 20.51%. closures with feed through. This in- AsshowninFigure4,theROV- By means of this, the MTBF of the creases the size, weight, and cost of TMS docking operation is supported ROV-TMS docking process can be the assembly, which are not preferred by a camera, lights, associated con- increased to 3.6 years. solutions. As a solution to this chal- trols and power systems located in d. By operating the ROV isolation lenge, an industrial standard 660 V, the TMS. It is calculated that the switchgear in the TMS as a switch 100 A motor air break low voltage TMS docking vision support has a From standards (U.S. Department contactor is selected and used in an probability of failure of 20.51%. of Defense, 1991), the FIT of the oil-filled, pressure-compensated envi- When this support system fails, the electric power contactor opening under ronment. As the dielectric capacity of pilotcannotdockbacktheROVto load is 10 times higher than when it is oil is 10 times that of air, this encour- the TMS, even if the other con- operated without load. The ROV op- ages the use of the 660 V air contactor ditions required for proper docking erates with a power of nearly 60 kW at at 6,600 V in a pressure compensated are maintained. To overcome this, near unity power factor for propulsion mode. The dimension of the selected black-dock sensors are introduced. and control systems. The remotely op- contactor used to carry out the me- The sensors are used to measure the erable isolating device in the TMS has dium voltage (MV) switching opera- following: to handle a maximum current of 10 A tion is approximately 0.2 m (L) × a. Tether cable tension. at 6,600 V. Using the conventional 0.11 m (W) × 0.1 cm (H).
60 Marine Technology Society Journal FIGURE 7
MTBF improvement by incorporating black-dock sensors.
The reliability of the MV switch- dition, resembling the required con- Paulo et al., 2001; Shukla et al., 2001). gear is of utmost importance in the dition of a MV switch. They are electrochemical, double layer overall system, as the failure of this FMECA studies revealed that pos- capacitors (Barrade et al., 2003; Rufer, contactor leads to the paralysis of the sible situations leading to the opening Hotellier, & Barrade, 2004; Weddell whole system. When the switchgear of the MV switch TMS located under et al., 2011; DeAnda et al., 2004), opens, an electrical arc is produced, load are as follows: which are preferable because they andthisisextinguishedbythearc- 1. Input power failure in the TMS offer high power and energy densities. chute mechanism and insulating oil. alone. The MV switch operates on 24 As the arc generates high tempera- 2. Control system failure in the TMS VDC supply and requires a maximum ture, it decomposes a portion of the oil alone. coil current of 0.2 A. The design criteria into gases (Thomas, 2008) composed 3. Accidental open command to the (Al-Ramadhan & Abido, 2012) involve of 70% hydrogen, 20% acetylene and MV switch. ensuring a minimum voltage of 12 V carbon particles. Carbon particles are To overcome the above situations, for continuous holding of the coil for conductive in nature. The quantity of a possible solution would be to delay duration of 60 s. Based on these param- decomposed carbon is a function of the opening of the switch by a few sec- eters, we have calculated the require- the arc intensity, duration of the arc onds, during which time the electrical ments of energy (W) and minimum and the temperature of the arc plasma. load on the MV switch will be reduced. capacitance (C). Twelve capacitors are Astheswitchgearisinaclosedoil This requires reliable localized energy connected in a series to get the effective system, prolonged usage or excessive storage in the TMS system. Even capacitance of 0.833 F that can hold the generation of carbon particles leads though batteries could be attractive in MV switch up to 60 s. The designed cir- to oil contamination and subsequent terms of size, they are not so attractive cuit incorporating the required protec- failures. Therefore, the longevity and in terms of reliability and safety. Super tion circuits is integrated into the TMS hence the reliability of the assembly capacitors are found to be the best control system. When a 24-V control can be improved by ensuring that the trade-off (Lemofouet & Rufer, 2006; command from the TMS is given, the switchgear opens under a no-load con- Mallika & Saravanakumar, 2011; MV switch coil gets energized. The
May/June 2013 Volume 47 Number 3 61 super capacitor is charged through a storage winch slip rings, and addi- When the ROV and TMS operate 50 Ω, 10-W resistor. In the event of tional optical cores in the tether at full electric load, the system is de- the 24 V control command failure, and umbilical cables. signed in such a way that the shipside the super capacitors will continue to b. A new RS485 link between the voltage is 6,600 V and the ROV and hold the MV switch coil by supplying ROV and the TMS processors TMS end voltage is 6,000 V, with an the stored energy through the diode. using the twisted pair electric cable umbilical cable voltage drop of 600 V. The super capacitors shall continue in the tether cable is established. At no load condition, the TMS and the to energize the contactor coil and, in From Figure 9, it can be seen that ROV systems experience a voltage of turn, hold the power contacts of the the ROV-Ship Console communication 6,600 V. This results in 10% increase switch in a closed condition for a period failure probability is 2.59%. By means in the 300 V circuits, which is not a of 60 s. The control system utilizes this of the improved architecture, the prob- healthy condition for the thruster period to reduce the electrical load on ability of failure is reduced from 2.59% motor power electric speed controller the MV switch, so that it operates at to 0.434%. system. no-load. The required logic is imple- With this improvement, the MTBF This overvoltage condition is man- mented in the logic controllers in the of the ROV-TMS docking process is aged by implementing the automatic ROV, the TMS and the ship. By means increased to 4.6 years. voltage compensation system on the of this, the probability of power fail- f. With voltage control devices on the ship side, using a high-frequency (hF) ure to the ROV is reduced from 26.4% top side and back-emf capacitors in power converter, which works on the to 12.8%. TMS and ROV 300 V circuits principle of v/f control philosophy. By means of this, the MTBF of Thruster motors are operated using The control methodology is imple- the ROV-TMS docking process can BLDC motor electronic controllers mented using a proportional-integral- be increased to 3.8 years. located in the ROV. Tether winch derivative (PID) controller, and the e. By having redundancy in the Ship- hydraulic motors are also operated by sameisshowninFigure10.Atno ROV optic link and a serial link the BLDC motor controllers located load condition, the system draws only between the ROV and the TMS in the TMS. The controllers are ener- the reactive current required to charge The ROV and TMS communi- gized by 300-V power supplies in the the cable capacitance. When the ROV cate with the ship system through the ROV and the TMS. The BLDC system gets loaded, there is an increase optical-based Ethernet network. The motor power electronic systems are intheactivecomponentoftheload topology in the base and improved sensitive to excess voltage. To improve current. The PID controller is tuned cases is shown in Figure 8. the reliability of the electronic control- to provide the control input to the gate In the base case, the ROV-Ship lers and subsequently the system reli- driver of the HF converter in such a network spans through the optical ability, voltage management systems way that 300 V is maintained constant core in the tether cable and in the um- are required. at the ROV and TMS ends. bilical cable, with one pass in the TMS Voltage management from the ship Voltage management on the subsea winchslipring,andoneinthedeck side is implemented as follows: side is implemented as follows: storage winch slip ring and to the In the ROSUB 6000 system, the Thrusters and pump motors in the ship console. The TMS-Ship network ship power at 415 V at 50 Hz is con- ROV and TMS are operated with spans through one pass in the TMS verted to 6,600 V at 460 Hz and trans- brushless DC motors, which are con- winch slip ring and in the deck storage mitted through the 7,000-m-long trolled by power electronics. The con- winch slip ring and one core in the umbilical cable and further to the trollers help in operating the systems at umbilical cable and then to the ship ROV through the 400-m-long tether the required speeds. A BLDC motor console. cables. The voltages are stepped down in operation produces back-emf volt- The improved design incorporates and rectified so as to obtain 300 V age (Brushless Direct Current Motor the following: and 24 V DC, suitable for operating manufacturer recommendations for a. Redundancy is introduced in the the propulsion thrusters and control thruster Power System reference), at ROV-Console communication systems. The ROV has an electrical the pulse width modulation (PWM) link, by having an additional opti- load of 70 kW and the TMS has a frequency. This back-emf has the ten- cal pass in the TMS tether and deck total load of 20 kW. dency to raise the overall 300 V DC
62 Marine Technology Society Journal FIGURE 8
Schematic of the network.
May/June 2013 Volume 47 Number 3 63 FIGURE 9 of 19.52%. By ensuring proper operat- ing voltage with the aid of the de- Tree indicating improvements in TMS-Console. scribed voltage management devices the probability of failure for each BLDCmotorcontrollerisreduced to 16%. With this improvement, the MTBF of the ROV-TMS docking process is increased to 4.8 years. g. With redundant TMS pump In the base case, the TMS system is equipped with one electric motor driven hydraulic pump, which is used foroperatingthetethercablewinch drum. With a redundant pump, the winch operation due to the electrical and corresponding control system failure is reduced from 9.96% to 1%. The same can be seen from the failure trees in Figure 11. With this improvement, the MTBF bus voltages to more than 600 V. This 80and20mFareconnectedacross of the ROV-TMS docking process is is detrimental to all the power elec- the DC buses permanently in the increased to 4.9 years. The same can tronics controllers connected to the ROV and TMS. In the base case, be seen from Figure 12. The stage by 300 V DC network. To counter this each BLDC motor power electronics stage improvement in the probability back-emf, the DC capacitor banks of controller has a probability of failure of failure and the corresponding MTBF can be found from Table 3.
FIGURE 10 Type 4 Failure Scenario: (a) Automatic Voltage Compensation implementation methodology. (b) Location of capacitors in Manipulator Operation Failure the subsea side. Normal Working Scenario The ROV in the ROSUB 6000 is equipped with two manipulator arms with five and seven functions for carry- ing out subsea operations. The manip- ulators are operated by the personnel from the control console using joy- sticks. In addition to other vision sys- tems, manipulator arms are equipped with a camera, which will give a real- time video feedback to the operating personnel. Figure 13 shows the work class ROVs with manipulators involved in different kinds of tasks. The subsea operations depend on the mission objective and may involve tasks such as electric wet mate con- nector mate/de-mate, pipe line valve
64 Marine Technology Society Journal FIGURE 11 operations and pipe line sacrificial anode fixing. Improvement in the failure rate with redundant pump improved case. Failure Scenario The risk involved in these subsea operations varies widely (API RP14B, 2012; NORSOK standard, 2001). Figure 12 shows the ROV holding one end of the wet mate cable connec- tor for mating with the fixed ROV panel. The other end of the cable could be a part of the permanent sub- sea installation. When the manipula- toroperationfailsinthiscondition, the forced retrieval of the ROV by winding back the tether or main um- bilical winch could damage the subsea installation. Such damages could turn disastrous for subsea oil and gas well- heads and manifolds. Thus, the ROV will be anchored to the subsea installa- tion, with other systems connected to the ROV deployment vessel. To miti- gate this situation, another intervention
FIGURE 12
Tree indicating improvement in the overall MTBF after introducing the redundant pump.
May/June 2013 Volume 47 Number 3 65 TABLE 3 ROV to the location of interest. Dur-
MTBF Improvements with modifications for TMS-ROV docking failure case. ing the process, based on the ROV heading with respect to the TMS, the Improvement Probability of Failure MTBF Kevlar-armored, torsionally balanced Base design case 92.48% 1.9 years tether cable will be subjected to twist- ing, and the number of twists depend By means maintaining spares for ship based 78.9% 3.3 years electric systems on the skill of the pilot, nature of the operation and the condition of the sea By operating ROV isolation circuit breaker as a 73.13% 3.8 years switch water currents. Further, as the TMS is connected to the deployment vessel, By having redundancy in Ship-ROV optic link and a 66.64% 4.6 years which is maintained in a dynamic serial link between ROV and TMS positioning mode, it may also create With voltage control devices in top side and 64.97% 4.8 years heading changes for the TMS with back-emf capacitors in ROV 300 V circuits respect to the ROV. Thus, the num- With redundant TMS pump 64.05% 4.9 years ber of twists depends on the relative 360 deg. heading counts. When the vehicle has to be dispatched for crisis 90.27% with a corresponding MTBF ROV has completed the mission, it management. A similar condition of 2.1 years. The network and hard- will be docked back to the TMS after could occur if the ROV operates an ware used for the ROV-TMS docking winding back all the reeled out cable. oil pipe line isolation valve, which function is shared by the manipulator Tether cables are designed to with- leads to valve damages and consequent system. Therefore, the system improve- stand specific twists per meter length oil leakages, if double barrier isolation ments discussed for Type 3 ROV-TMS (Buckham et al., 2003; Sakamot et al., is not provided. The same could be docking failure apply equally for reduc- 2008). When the number of twists/ risks involved during salvage opera- ing the manipulator operation failure. meter exceeds the design limit, the tions. Therefore, the reliability of the It can be seen from Figure 14 that cable sheath and, hence, the cable manipulator system has to be high. the manipulator operation failure prob- will be damaged. Thus, to avoid cable ability is reduced to 55% with a cor- damage, the pilot has to ensure that Base Case responding MTBF of 6.2 years. The there is no residual twist on the cable The following could lead to manip- improvement with each change is before docking. ulator operations failure: listed in Table 4. To aid in a hassle free dock, the a. Manipulator functional failure. following parameters are monitored b. Hydraulic pump motor electric by the control system: system failure. Maintainability a. ROV heading counts provided by c. Manipulator operation vision sup- Importance of Cable Twist the heading sensor in the ROV. port failure. Monitoring Mechanism b. TMS heading counts provided by In the base case, the ROV manipula- When the ROV is undocked from the heading sensor mounted in tor control failure is calculated to be the TMS, the pilot will maneuver the the TMS. c. Length of the cable reeled out of FIGURE 13 the drum, which is provided by the tether cable layer counter. Typical ROV manipulator in operation (Courtesy: WHOI and MBARI websites). d. Cable tension which is provided by the load cell sensor mounted in the winch. As the heading sensors and electronic counting are done in the ROV and TMS, a power interruption to the ROV and TMS will result in the loss of twist count information. Even
66 Marine Technology Society Journal FIGURE 14
ROV manipulator control failure for the base and improved cases.
though the last logged value could be Figure 15 shows the heading counts failure rates of the tether cable. This made available in the shipside, once monitoring mechanism and the sea is given to indicate the impact of the the power resumes, the number of battery in the ROV. tether cable failure on the overall sys- heading changes undergone by the By means of introducing the sea tem MTBF. ROV during the interruption period battery, the probability of power As it is understood that the tether will not be known. Therefore, the failure to the ROV control systems is cable is an important component residual twists on the cable will not reduced from 15% to 5%. Thus, the having a significant role in the MTBF, be available to the pilot during the twist feedback information failure systems are incorporated that can final docking stage. To overcome this probability to the pilot is reduced measure the cable electric insulation problem and to avoid power interrup- from 60% to 55%. and optical losses in the system online. tion to the heading sensor and moni- Table 5 shows the MTBF of the As the cable performance depends on toring electronics, a sea battery is ROV-TMS docking process and the operating ambient condition, the used as a backup power in the ROV. manipulator operation with different inclusion of this mechanism will be useful for the system safety as well as TABLE 4 for preventive maintenance action.
MTBF improvements with modifications for manipulator function failure case.
Improvement Probability of Failure MTBF Preventive Maintenance Decision Support Base design case 90.27% 2.1 years Table 6 shows the probability of By means of maintaining spares for ship based 71% 4.1 years failure in percentage for the ROV- electric systems TMS docking process for different By operating ROV isolation circuit breaker as a 64.7% 4.8 years periods. The table also details the role switch of the subcomponents. By having redundancy in Ship-ROV optic link and 64% 5.0 years The cells with data in bold fonts a serial link between ROV and TMS indicate the failure rates of the com- With voltage control devices in top side and 55.11% 6.2 years ponents whose failure probabilities back-emf capacitors in ROV 300 V circuits are higher.
May/June 2013 Volume 47 Number 3 67 FIGURE 15 Preventive Maintenance Schedule Summary ROV and TMS having independent heading sensing systems and the location of the sea battery in the ROV. Umbilical and Tether Cables Thelongevityofthetethercable depends on the handling and electrical stresses. Handling stresses are due to twisting and can be optimized by skilled piloting. The failure rates of the umbil- ical and tether cables were obtained from OREDA and are used for the calculations. Andrew Bowen et al of WoodsHoleOceanographicInstitu- tion (WHOI) and Ed Mellinger et al. of Monterey Bay Aquarium Research TABLE 5 Institute (MBARI) performed the insu- Impact of tether cable failure in failure cases under study. lation life testing of field-aged samples of cables used in MBARI Tiburon ROV ROV-TMS Docking Manipulator Operation and WHOI Jason ROVs, which have Times Tether Probability of MTBF Probability of MTBF an accumulated time of 6,700 h in Failure FIT Failure (%) (years) Failure (%) (years) 230 dives. The tests identified factors ×1 64 4.9 55 6.3 affecting the insulation stress at the op- ×2 65 4.8 56 6.1 erating voltage and high hydrostatic pres- ×5 67 4.5 58.5 5.7 sures. It was calculated that the cable could survive for 22.8 years under dry ×10 70 4.1 62.4 5.1 aging conditions but would survive only ×20 75 3.6 67 4.5 for 7.6 years when operated at 400 Hz
TABLE 6
Maintenance decision support table.
Probability of Failure in % System/Component 1 year 3 years 5 years 10 years 15 years
ROV-TMS docking 18.1 45.4 64.0 87.6 93.5 Subcomponents Cable termination 0.064 0.18 0.30 0.60 0.90 Tether cable 0.38 1.14 1.9 3.76 5.59 Umbilical cable 0.21 0.63 1.06 2.11 3.15 HF converter 16.1 41.1 58.6 82.9 92.9 LV isolator 0.32 0.98 1.6 3.24 4.82 HV transformer 0.58 1.7 2.9 5.72 8.46 BLDC motors 0.39 1.18 2.01 3.9 5.8 Electrical slip ring 1.54 4.56 7.48 14.4 20.8 Power contactor 0.4 1.3 2.2 4.28 6.35 Plasma display 0.44 1.2 2.31 3.18 4.73 continued
68 Marine Technology Society Journal TABLE 6
Continued
Probability of Failure in % System/Component 1 year 3 years 5 years 10 years 15 years
Computers 0.45 1.35 2.2 4.45 6.6 PLC processor with memory 0.3 0.71 1.05 1.8 2.5 NI CPU IO modules 0.021 0.06 0.1 0.2 0.31 Thrusters BLDC motor power electronic controller 0.37 0.82 1.03 2.03 2.31 Fuses 0.008 0.026 0.043 0.087 0.13 Halogen lamp 0.017 0.052 0.087 2.13 2.59 Multiplexer power board 0.025 0.076 0.12 0.025 0.38 Multiplexer data board 0.079 0.23 0.39 0.79 1.18 Multiplexer video board 0.007 0.02 0.03 0.07 0.1 Real-time controller 1.11 3.31 5.46 10.64 15.53 Sea battery 8.8 24 37 60 75 Proximity sensor 0.052 0.15 0.26 0.52 .78 Fiber optic rotary joint 1.92 5.66 9.26 17.6 25.3 Photonic inertial navigation sensor 25.3 58.4 76.7 96.4 98.8 in a continuous deep water environment. The failure rates are used from a stan- number of charge-discharge cycles and Based on this experience, we have esti- dard obtained from the studies made the depth of discharge. In our appli- mated the tether cable replacement pe- for the U.S. Department of Energy- cation, the battery is subjected to very riod for the ROSUB6000 as 10 years. Energy Storage Studies program minimal stresses in terms of the depth (DeAnda et al., 2004), which consid- of discharge and duty cycle. Based on Sea Battery ers battery failure rates, when used in this experience, we have estimated the A sea battery has a failure rate of an UPS and similar applications. Lead sea battery replacement period for the 8.8% in the first year of operation. acid battery life depends highly on the ROSUB 6000 as 3 years.
TABLE 7
Summary of failures with probabilities of failure.
Base Case Improved Case Failure Type Failure Description Probability of Failure MTBF Probability of Failure MTBF
1 Camera not available for operation 83.51% 2.8 years 7.25% >10 years in ROV 1 Halogen Lamp not available for 83.40% 2.8 years 7.12% >10 years operation in ROV 2 Visual survey failure 98.86% 1.1 years 53.34% 6.6 years 2 SONAR bathymetric survey failure 97.87% 1.2 years 78.05% 3.3 years 2 Gas hydrate survey failure 98.89% 1.1 years 53.73% 6.5 years 3 ROV-TMS subsea docking failure 92.48% 1.9 years 64.05% 4.9 years 4 ROV manipulator operation failure 90.27% 2.1 years 55.11% 6.2 years
May/June 2013 Volume 47 Number 3 69 Summary and Conclusions ergy storage system. In: International Confer- International Offshore (Ocean) and Polar This paper describes the method- ence on renewable energies and power quality Engineering Conference, pp. 206-212. Beijing, – ology of RAM studies carried on the (ICREPQ), Spain, 28 30 March 2012, pp. 1-4. China: International Society of Offshore and Spain: European Association for the Develop- Polar Engineering (ISOPE). ROSUB 6000 deep water work class ment of Renewable Energies, Environment ROV system. Table 7 summarizes all Mellinger, E., Aabo, T., Bowen, A., Katz, C., and Power Quality (EA4EPQ). types of failures studied, the probability & Petitt, R.A., Jr. 2010. High Voltage Testing of failures and the MTBF in the base API RP14B, American Petroleum Institute. of an ROV electro-optic tether cable. MTS. case and improved cases. 2012. API Recommended Practices for Design, 28(9):4-5. Installation, Repair and Operation of Sub- The technical challenges in achiev- NORSOK standard. 2001. Risk and Emer- surface System. Pennsylvania: American ing the best possible MTBF for the gency Preparedness Analysis. Norway: Petroleum Institute. 30 pp. critical failures are explained in detail. Norwegian Technology Centre. The maintenance decision support table Barrade, P., & Ruffer, A. 2003. Current OREDA AUTOR. 2003. OREDA. SINTEF. details the operational personnel for the capability and power density of supercapaci- fi 835 pp. upkeep of the systems during the indi- tors: Considerations on energy ef ciency, ref. ISBN 90-75815-07-7. Pages 3,4. cated maintenance interval, so that the Paulo, F.R., Brian, K.J., Maiiesa, L.C., ş highest possible reliability is maintained Buckham, B.J., Driscoll, R.F., Nahon, M., & Ay en Basa, A., & Yilu, L. 2001. Energy during the mission period. The impor- Radanovic, B. 2003. Three dimensional dy- Storage Systems for Advanced Power Appli- cations. IEEE Proceedings. 89(12):3-4. tance of monitoring the tether cable namic simulation of slack tether cable in an ROV system. In: Proceedings of ISOPE 2003, healthiness during normal and wind- Ramesh, R., Jayakumar, V.K., Manecius, S., Hawaii, USA, Department of Mechanical ing operations, and the systems imple- Doss Prakash, V., Ramadass, G.A., & Atmanand, Engineering, Vol. 2, pp. 2-3. Victoria BC, mented for effectively monitoring and M.A. 2010. Distributed Real Time control Canada: University of Florida. maintaining the tether cable’sopera- systems for deep water ROV (ROSUB 6000). tional and functional healthiness, using DeAnda, M.F., Miller, J., Moseley, P., & In: 7th International Conference on Com- the tether cable pay-out, vehicle head- Butler, P. 2004. Reliability of Valve-Regulated putational Intelligence, Robotics and Auton- omous Systems (CIRAS) in 13th FIRA Robot ing, electric insulation and optical per- Lead-Acid Batteries for Stationary Applica- tions. California: Sandia National Laboratories. World congress, Proceedings, pp. 33-40. formance sensors with the aid of a sea 68 pp. http://dx.doi.org/10.2172/918779. New York: Springer. battery, is also discussed. FIDES Guide. 2009. Reliability Methodology Rufer, A., Hotellier, D., & Barrade, P. 2004. for Electronic Systems. FIDES group. 465 pp. A super capacitor based energy storage sub- Acknowledgments IEEE. 1997. IEEE Standard 493-1997, Recom- station for voltage compensation in Weak The authors gratefully acknowledge mended Practice for the Design of Reliable In- Transportation networks. IEEE T Power Deliv. the support extended by the Ministry of dustrial and Commercial Power Systems, IEEE 19(2):629-36. Earth Science, Government of India in Standards Boards. Available at: http://standards. Sakamot, K., Fujimoto, Y., & Osawa, H. fi funding this research. The authors also ieee.org/ ndstds/standard/493-2007.html. 2008. Development of fatigueless umbilical wish to thank the other staff involved Lemofouet, S., & Rufer, A. 2006. Hybrid cable for full ocean depth 12000 m. in the project for their contribution and Energy Storage system based on compressed In: Marine cable Development Section support. air and supercapacitors with maximum effi- Engineering Department, Furukawa Electric cient point tracking. IEEE T Ind Electron. Co. Ltd, Japan, Advanced Underwater 53(4):1105-15. Vehicle R and D Group, JAMSTEC, Japan Corresponding Author: in International wire and cable 57th Sym- Mallika, S., & Saravanakumar, S. 2011. Narayanaswamy Vedachalam posium proceedings, pp. 2-4. Eatontown, NJ: Review of ultracapacitor—Battery interfaces for National Institute of Ocean Technology IWCS Inc. energy management system. Int J Eng Technol. Chennai, India 3(1):2-3. Shukla, A.K., Sampath, S., & Vijayamohanan, Email: [email protected] K. 2001. Electro-chemical capacitors: Energy Manecius, S., Ramesh, R., Subramanian, A.N., Storage and beyond batteries. Curr Sci. Sathianarayanan, D., Harikrishnan, G., 79(12):37-38,41. References Jayakumar, V.K., … Amiragov, A. 2010. Al-Ramadhan, M., & Abido, M.A. 2012. Technology tool for deep ocean exploration— Tecnadyne Application Note AN601. 2006. Design and simulation of super capacitor en- remotely operated vehicle. In: Twentieth General Power System Wiring Practices
70 Marine Technology Society Journal Applied to Tecnadyne DC Brushless Motors. San Diego, CA: Tecnadyne, Inc.
Thomas,A.P.2008.OilCircuitBreaker Diagnostics. In: 7th Annual Wiedmann Technical conference, pp. 1-2, 5. New Orleans: Weidmann Inc.
U.S. Department of Defense. 1991. Military Handbook, Reliability Prediction of Elec- tronic Equipment. Washington, DC: Author.
Weddell, A.S., Merrett, G.V., Kazmierski, T.T., & Al-Hashimi, B.M. 2011. Accurate supercapacitor modeling for Energy harvesting wireless sensor nodes. IEEE T Circuits-II. 58(12):2. http://dx.doi.org/10.1109/TCSII. 2011.2172712.
May/June 2013 Volume 47 Number 3 71 PAPER Anchor Drop Tests for a Submarine Power-Cable Protector
AUTHORS ABSTRACT Han-Sam Yoon Submarine power cables are widely used for power transmission, such as Research Center for Ocean between mainlands and offshore islands and from offshore wind farms to on-land Industry and Development, substations. There are several ways to protect power cables from accidental loads. Pukyong National University, Protection includes concrete blankets, sand bags, bundles, tunnel-type protectors, Busan, South Korea and trenching. However, no design standard for power-cable protectors is currently Won-Bae Na available because of the varieties of cable protection solutions and man-made or Department of Ocean Engineering, natural hazards to submarine power cables. Thus, this paper presents anchor Pukyong National University, drop tests for a newly designed, matrix-type submarine power-cable protector Busan, South Korea assembled with reinforced concrete blocks, to make a safety assessment. Marine environments were surveyed at the target site and simulated in the test set-up. A 2-ton stock anchor was selected as the colliding object, and a 25-ton crane was Introduction prepared to drop the anchor. Preliminary tests were performed to investigate the nchoring activities—colliding effect of soil composition and protector arrangements on the test results. Finally, fi and dragging—have become the larg- four eld anchor drop test scenarios were designed, carried out, and analyzed, and a A safety assessment was made for the submarine power cable. From the tests, it was est cause of submarine cable faults in recent years (International Cable found that, in addition to falling distances, the soil composition and saturation were fi Protection Committee, 2009). To pre- signi cant factors for the settlement depth and damaged areas. Considering the vent power cable failures from this settlement depth of soils, the damaged areas of the concrete blocks, and the dam- cause, the International Cable Protec- aged state of the pipes (safety zone), all of the test results showed that the mattress tion Committee (ICPC) suggests the failed to protect the power cable from the anchor collision. The deformation, dam- use of automatic identification systems age, and breakage of the pipe, which simulated the safety zone of the power cable, (AISs) for vessels. Nevertheless, the use gave clues as to the reasons for the failure. fi of AISs is not applicable to small ships, Keywords: anchor drop, eld test, submarine power-cable protector, stock anchor and their use has not spread rapidly in some developing and even industrialized countries (Coffen-Smout & Herbert, Yao-Tian, 2012). Similarly, in 2006, island, and the power-supply black- 2000; International Cable Protection one of two submarine power cables out caused a simultaneous suspension Committee, 2009; Wagner, 1995). connecting the main Korean Peninsula of water availability. This is a serious issue, because cable to Jeju Island was damaged by ship an- Such accidents are also applicable failures can lead to significant inconve- choring activities. This event caused a to the power cables transporting off- nience to residents, cutting communi- power-supply blackout for the whole of shore wind power to a national grid cations, power, and water supplies. For Jeju Island, resulting in severe inconve- on land. Moreover, given the current example, in 2010 the submarine power nience to nearly 570,000 residents increasing trends in offshore wind- cable linking Shanghai and Shengsi and 30,000 tourists. Fortunately, no energy projects, offering security against Island, Zhejiang, was fouled and broken loss of human life was reported dur- many energy-supply emergencies— completely as a result of ship anchor- ing that period, likely because the whether natural or man-made—is a ing. The island lost its power supply outage lasted only 2.5 h during the significant issue. Thus, there has been for 4 days, and then electricity was only daytime (Woo et al., 2009). How- much work to assess the causes of dam- partially restored to about 90,000 resi- ever, it was certainly undesirable be- age and to improve cable protection. dents using diesel generators (Jie & cause tourism is important to the The possible causes—anchor collision
72 Marine Technology Society Journal and dragging—have been investigated tricity to a high voltage (about 33 kV) safety evaluation guideline for sub- and design criteria for submarine and sends it 8–16 km to a national marine power cable protection, and as- power-cable protectors have been im- or international grid at a substation sociated projects will launch in 2013. proved in South Korea (Woo et al., on land (Byrne & Houlsby, 2012; The safety guideline will be completed 2009). This extensive research has in- Esteban et al., 2011; Yamabuki & in 2015. cluded computer simulations of an- Kubori, 2012). Because wind speeds There is no international design chor collision and dragging on cable tend to increase significantly with dis- guideline and standard. At the Subsea protectors (Woo & Na, 2010). How- tance from land, the offshore wind re- Power Cables Conference in London ever, numerical simulations alone are sources can generate more electricity (April 2012), a roundtable discussion not fully reliable because it is not easy than wind resources at adjacent land- dealt with the necessities of interna- to make definite safety or failure as- based sites. This means the length of tional standards set for cable installa- sessments based solely on numerical the power cables will increase, and so tion projects. The burial protection results, such as stress contour and de- will the need for cable protection. index was suggested as a power cable formation patterns. The test process and results can pro- protection solution, but this method Thus, in this study, field anchor vide a valuable checkpoint for manag- is conceptual. Sharples (2011) empha- drop tests of a newly designed subma- ing the electrical power supply from sized the fact that different cable pro- rine power-cable protector were inves- the mainland to an island and from tection technologies developed over tigated. For this purpose, the following an offshore wind farm to an on-land time lend themselves to specific condi- works were carried out: (1) material station. tions and scenarios. These include preparation and test set-up, (2) field rock dumping, preformed concrete anchor drop tests, and (3) safety as- mattress, assisting natural sedimenta- sessment. For material preparation, a Current Practice tion with frond mats, durable padding mattress-type power-cable protector In South Korea, there is no a spe- or grout-filled bags, external plastic was selected, designed to allow adjust- cific design guideline and standard (polyurethane) or metal sheathing on ment of its horizontal and vertical for power cable protectors. After KT thecable,heavyarmoringbuiltinto lengths by controlling the number of Submarine (a Korean company) was the cable itself, and custom solutions. reinforced concrete blocks used. This established in 1994, submarine power Det Norske Veritas (DNV) published adjustability allows the blocks to be as- cable installation and maintenance the recommended practice DNV-RP- sembled in the field, using hooks and have been practiced under the super- F401 (Electrical Power Cables in Subsea links, into different sizes of protectors vision of the Korea Electric Power Applications, 2012). The recom- in a designated field environment after Corporation (KEPC). However, the mended practice (RP) focuses not on installing the power cables on the sea- design practice has not yet been estab- cable protection but on the electrical bed. In the field tests, first, the termi- lished because of the lack of data and power cables themselves. Because of nal velocity of a 2-ton stock anchor in studies. Although all of the power the varieties in cable protection solu- water was calculated and converted the cables in South Korea have been oper- tions and man-made or natural haz- velocity into a corresponding falling ated and maintained by KEPC since ards to submarine power cables, it is distance in air. Second, the soil proper- 1979, the first major issue on power hard to set the design guideline and ties were surveyed at the target site— cable design came up in 2006, after standard. Therefore, at the moment, Haenam, in the Southwest corner of the failure of the cable between Henam most work focuses on mitigating the the Korean Peninsula. Third, by rec- and Jeju. From the accident, it was risk of cable damage through cable ognizing the fundamental behaviors found that the concrete mattresses in- protection solutions and planning the of the protector, an experimental set-up stalled were not good enough to en- best cable route, etc. was designed. dure current anchor specifications However, Det Norske Veritas pub- This study should be relevant to and activities. That is why this study lished a related recommended practice the offshore wind power industry, investigated the newly designed cable DNV-RP-F107 (Risk Assessment of where submarine cables take power protector. With the series of field an- Pipeline Protection, 2010). This recom- to an offshore transformer and the off- chor collision and dragging tests, the mended practice has a chapter called shore transformer converts the elec- Korean government is focusing on a “Pipeline and Protection Capacity,”
May/June 2013 Volume 47 Number 3 73 which deals with steel pipeline, flexible FIGURE 2 shaped hooks were connected to the pipeline, umbilicals, and different pro- reinforcing bars (Figure 2c). Materials and facilities: (a) assembly of 70 tection methods. Here, umbilicals are blocks (5 EA × 14 EA), (b) circular links and Concrete is often considered to typically a complex compound of tub- arch hooks used to assemble each block, the ultimate construction material, be- ing, electrical wires, reinforcement, (c) array of reinforcing bars and hooks in cause of its considerable strength, rela- and protective layers. In other words, each concrete block, (d) 2-ton stock anchor, tively low cost, and virtually limitless umbilicals consist of hydraulic lines and (e) 25-ton crane. design capabilities. When subjected used to transfer chemicals and fluids to an impact or collision, concrete is and electric and fiber optic components generally submitted to both a multi- to monitor pressure, temperature, flow axial state of stress characterized by a and vibration, while submarine power high mean stress and high strain rates. cables are used for transmission of elec- It is known that the only material pa- tric power. Therefore, the recommended rameter governing impact resistance of practice can be useful to develop the concrete structures is based on the uni- design practice of submarine power axial unconfined compressive strength cable protection. of concrete (Daudeville & Malécot, 2011). Therefore, it is necessary for concrete to have a significant increase Material Preparation in its toughness, hence impact resis- and Test Set-up tance (Liu et al., 2012). Field drop tests on the protector A dimensional description of the blocks between the left and right blocks. were carried out in an open space. power-cable protector is shown in Fig- These arrangements were designed to For the field-test set-up, a 2-ton stock ure 1. The proposed mattress-type pro- change the size of the protector. The anchor (KS V3311, 2006) and a 25-ton tector was assembled from 70 blocks assembly could be performed on a ves- crane (Figures 2d and 2e) were pre- (5EA×14EA),asshowninFigure2a. sel using circular links and arch hooks pared. To analyze the movements of Here, the first notation (5 EA) indicates (Figure 2b). the protector and anchor, a camcorder the number of blocks in the y direction Each block was 0.5 m (length) × was used. (width), and the second notation (14 EA) 0.5 m (width) × 0.1 m (depth) and was It should be noted here that, instead indicates the number of blocks in the manufactured from reinforced concrete of a water environment, tests were car- x direction (length). There were three to increase its compressive and ten- ried out on land because otherwise it types of blocks—left, basic, and right— sile strengths. The design concrete would be quite difficult to observe the meaning that each column consisted compressive strength was 52 MN/m2. state of the protector during the anchor of one left, one right, and three basic The reinforcement array is shown in drop process. To accommodate the Figure 2c. Here, the tensile strength water environment, the effect of water FIGURE 1 of the reinforcing bars (SD 400) was resistance on the anchor was considered 560 MN/m2, the diameter was 13 mm, in the test by facilitating the soil condi- Dimensional description of the mattress-type and the entire length of the reinforc- tions of the target sites and converting power-cable protector. ing bars was 6.274 m in each concrete the terminal velocity of the anchor block. The hooks were zinc-coated, in water into a falling distance of the cold-drawn, round steel bars with a anchor in air. tensile strength of 686 MN/m2 and a To simulate the soil conditions on diameter of 16 mm. Once the rein- the target seabed (Haenam), the soils forced concrete blocks were manufac- were surveyed and the soil composi- tured, these arch-shaped hooks were tions were obtained using the American linked by the circular links (Figure 2b) Association of State Highway and so that the blocks were assembled and Transportation Officials (AASHTO) extended to the mattress. These arch- soil classification method (Table 1).
74 Marine Technology Society Journal TABLE 1 the test results were assumed minor;
Soil composition at the target site. hence, these were not considered in the tests. Sediment Texture (%) Before carrying out the field tests, Ground Gravel Sand Silt and Clay two preliminary tests were performed, designed as shown in Table 3, to Case 1 49.62 (≈50) 49.88 (≈50) 0.5 (≈0) pinpoint the measuring points and ≈ ≈ ≈ Case 2 2.89 ( 3) 96.81 ( 97) 0.3 ( 0) deformation patterns. The effects of variations in the soil composition However, in the field tests, approximate to be located not only at the target (Case 1 and Case 2) and mattress spec- values were used instead of the exact site but also at other sites. Thus, in ifications(3EA×3EAand5EA× percentage of each sediment texture addition to 5 m, 9 m was used as a 14 EA) were also investigated. Other (Table 1). Case 1 had 50% gravel and falling distance in the tests. factors, such as the soil condition and 50% sand, while Case 2 had 3% gravel Considering the added mass effects falling distance, were fixed as dry and and 97% sand. In addition to the com- on the tests, it should be noted that the 10 m, respectively. In the preliminary position, the soils were classified into stock anchor reaches the falling state tests, the safety assessment was made dry and saturated states by adjusting with a constant falling velocity (the ter- through the failure of blocks and the their water content. However, the de- minal velocity) in the target sites. In resulting settlement depth and shape. gree of saturation was not recorded in other words, the anchor is not acceler- Unlike the main test program, a plas- detail; only rough descriptions—dry ating before colliding. As this happens, tic pipe under the mattress was not and saturated—were used in the tests. the effect of the added mass on the installed. Considering the tidal effects on the anchor is not significant. Therefore, Finally, a criterion was decided for water depths at the target site, it was the effects of the added mass on the the safety or failure assessment of the assumed that the terminal velocity test results were not considered in the protector after collision with the 2-ton was the design velocity of the stock test. In addition, because of the pres- stock anchor for the main test program. anchor. However, in the calculations, ence of water, pressure effects in deep For the assessment, a safety zone was it was not easy to determine the drag water and the resulting soil behavior introduced along the center of the coefficient of the stock anchor because are other factors to be considered in power-cable location. To simulate this, of its unusual shape. Thus, a range the tests. However, their effects on a plastic pipe was embedded below the of drag coefficients, from 0.7 to 1.7 (Table 2), was introduced to investi- TABLE 2 gate a range of terminal velocities. By making use of the principle of energy Terminal velocity and falling distance with respect to drag coefficient.
conservation, the falling distances in Drag Coefficient Terminal Velocity (m/s) Energy (J) Falling Distance (m) air were calculated, ranging from 1.78 to 4.32 m. Because of the maximum 0.7 9.856 84755 4.32 value of 4.32 m (4.96 m in water), a 0.8 9.219 74153 3.78 falling distance of 5 m was considered 0.9 8.692 65918 3.36 fi in the eld tests. This selection was 1.0 8.246 59326 3.03 conservative in the sense that the cor- 1.1 7.682 53930 2.75 responding drag coefficient to the maximum falling distance was 0.7, 1.2 7.528 49445 2.52 which is much smaller than the drag 1.3 7.232 45633 2.33 coefficients of a C-section (2.30 or 1.4 6.969 42374 2.16 1.20), square prism (2.05 or 1.05), 1.5 6.733 39553 2.02 and disk (1.17) (Fox et al., 2004). 1.6 6.519 37078 1.89 However, it should be emphasized here that the protector was designed 1.7 6.324 34893 1.78
May/June 2013 Volume 47 Number 3 75 TABLE 3 FIGURE 4
Preliminary drop tests. Test result P1 (falling distance: 10 m, soil: Case 1, mattress 3 EA × 3 EA). Mattress Specifications Soil Soil Falling Identity Condition Composition Distance No. of Rows No. of Columns
P1 Dry Case 1 10 m 3 3 P2 Dry Case 2 10 m 5 14
TABLE 4 cause of the broken blocks under the Anchor drop test scenarios. mattress and because of the settlement depth and shape. Mattress Specifications Soil Soil Falling A detailed description of P2 is pro- Identity Condition Composition Distance No. of Rows No. of Columns vided in Table 3. For the test, the dry T1 Dry Case 1 5 m 5 14 soil composition of Case 2 was prepared below the mattress and the stock an- T2 Dry Case 1 9 m 5 14 chor was dropped from 10 m. Here, a T3 Saturated Case 2 5 m 5 14 5 EA × 14 EA mattress was prepared. T4 Saturated Case 2 9 m 5 14 The protector was damaged (Figure 5), and the blocks near the collision area were broken. Two blocks were totally mattress. The mattress was assumed to A detailed description of P1 is pro- crushed (Figures 5a and 5b). After re- have failed if the anchor and broken vided in Table 3. For the test, first, the moving the protector (Figures 5c and concrete blocks delivered a compres- dry soil composition of Case 1 was pre- 5d), the measured maximum vertical sive force to the pipe. In total, four pared below the mattress and the stock soil settlement was 37 cm. The vertical scenarios were designed to provide a anchor was dropped from 10 m. In this settlement differed from that in P1, al- safety assessment of the protector case, a 3 EA × 3 EA mattress was pre- though the falling distance of T1 and under anchor drops with the two-ton pared instead of a 5 EA × 14 EA. As a T2 was the same. It happened because stock anchor (Table 4). result (Figure 4), the blocks near the of the difference in the soil composi- collision area were broken, and three tion between T1 and T2. That is, the blocks were crushed (Figure 4a). After soil composition of Case 2 (gravel 3% removing the protector (Figure 4b), and sand 97%) was much weaker than Drop Test Results the measured maximum vertical soil The field tests, described in Tables 3 settlement was 7 cm. Despite the rela- and 4, were carried out on open land at tively shallow settlement, the protector Pukyong National University, located FIGURE 5 failed to protect the power cable be- in Busan. As described earlier, a 25-ton Test result P2 (falling distance: 10 m, soil: crane was used to drop the two-ton FIGURE 3 Case 2, mattress 5 EA × 14 EA). stock anchor to the protector. Before carrying out the four drop scenarios A typical anchor drop process between the (Table 4), preliminary drop tests were anchor and protector. performed to investigate damage pat- terns, determine measuring points, and assess the effects of soil composi- tions. Figure 3 shows a typical colliding sequence or process. In all of the tests, the same colliding process occurred, as follows.
76 Marine Technology Society Journal that of Case 1 (gravel 50% and sand FIGURE 7 Considering T4 (Table 4), the sat- 50%). For Case 2, the mattress pro- urated soil composition of Case 2 was Test result T2 (falling distance: 9 m, soil: tector also failed to protect the power Case 1, mattress 5 EA × 14 EA). prepared below the mattress and the cable because of the broken blocks stock anchor was dropped from 9 m under the mattress and the settlement (Figure 9a). The mattress arrangement depth and shape. was 5 EA × 14 EA. The blocks near the Considering T1 (Table 4), the dry collision area were broken (Figure 9b), soil composition of Case 1 was pre- resulting in a damaged area that was pared below the mattress and the stock 130-cm long and 50-cm wide, for a anchor was dropped from 5 m (Fig- total area of 6,500 cm2 (Figure 9c). ure 6a). The mattress arrangement After removing the protector, it was was 5 EA × 14 EA. Blocks near the found that the measured the max- collision area were broken (Figure 6b), imum vertical soil settlement was resulting in a damaged area that was 35 cm and the embedded pipe was 90-cm long and 17-cm wide, for a severely damaged (Figure 9d). total area of 1,530 cm2 (Figure 6c). mum vertical soil settlement was 7 cm After removing the protector, it was andtheembeddedpipewasseverely found that the measured maximum damaged (Figure 7d). Safety Assessment vertical soil settlement was about Considering T3 (Table 4), the sat- The anchor drop test results are 5 cm and the embedded pipe was dam- urated soil composition of Case 2 was summarized in Table 5. As shown in aged (Figure 6d). prepared below the mattress and the the table, all of the test results showed Considering T2 (Table 4), the dry stock anchor was dropped from 5 m the failure of the mattress power-cable soil composition of Case 1 was pre- (Figure 8a). The mattress arrangement protector under the anchor drop sce- pared below the mattress and the was 5 EA × 14 EA. The blocks near the narios tested. This failure assessment stock anchor was dropped from 9 m collision area were broken (Figure 8b), was due to the excessive compressive (Figure 7a). In this case, a 5 EA × resulting in a damaged area that was force on the pipe under the mattress, 14 EA mattress was prepared. The 96-cm long and 32-cm wide, for a with permanent deformation and blocks near the collision area were bro- total area of 3,072 cm2 (Figure 8c). breakage of the pipe. The collision ken (Figure 7b), resulting in a damaged After removing the protector, it was forces on the reinforced concrete blocks area that was 90-cm long and 28-cm found that the measured maximum transferred to the soil and obviously to wide, for a total area of 2,520 cm2 (Fig- vertical soil settlement was 13 cm the pipe. To help assess the test results, ure 7c). After removing the protector, and the embedded pipe was severely Figure 10 shows the settlement depth it was found that the measured maxi- damaged (Figure 8d). and damaged area, respectively, versus
FIGURE 6 FIGURE 8 FIGURE 9
Test result T1 (falling distance: 5 m, soil: Test result T3 (falling distance: 5 m, soil: Test result T4 (falling distance: 9 m, soil: Case 1, mattress 5 EA × 14 EA). Case 2, mattress 5 EA × 14 EA). Case 2, mattress 5 EA × $214 EA).
May/June 2013 Volume 47 Number 3 77 TABLE 5
Failure assessment.
Soil Falling Damaged Settlement Failure Identity Description Distance (m) Area (cm2) Depth (cm) Pipe State Assessment
T1 Dry Case 1 5 1,530 5 Damaged Failed T2 Dry Case 1 9 2,520 7 Damaged Failed T3 Sat. Case 2 5 3,072 13 Damaged Failed T4 Sat. Case 2 9 6,500 35 Damaged Failed the falling distances (5 and 9 m). From because it is directly related to the im- sized here that reinforced concrete the figures, the increase in falling dis- pact energy. The anchor velocity in structures in water generally deterio- tance increased the settlement depth water was converted to the velocity in rate as time goes. Thus, it is expected and damaged area, although the slopes air (Woo & Na, 2010). In that sense, that the protector in water will have differed. Considering the effect of the the water effect on the impact was con- different reaction to anchor collision soil conditions and composition, the sidered. In tunnel-type protectors, during its service life. However, Kim saturated Case 2 (gravel 3% and sand power cables do not have to be embed- et al. (2008) reported that reinforced 97%) gave deeper settlement depths dedintheseabed.Inmostcases,the concrete reefs, immersed in seawater and wider damaged areas than the protectors cover the power cable, for 18–25 years, have sound physical dry Case 1 (gravel 50% and sand which is located on the seabed. Thus, and chemical properties. Nonetheless, 50%) did. It was shown that this was the main energy dissipation is accord- in this field study, there were only lim- mainly due to the soil composition ef- ing to the toughness of the concrete ited test cases to distinguish the effects fect in addition to soil saturation be- mattress. However, as shown in the of soil composition and saturation on cause, in the preliminary tests, Case 2 test results, soil composition and soil the test results. gave a deeper depth (37 cm) than saturation had effects on the test re- Considering the test results, the Case1(7cm)did,althoughthesoil sults. In that sense, the water effect newly designed protector should be conditions were dry. on the soil was partially considered in modified and the burial condition of In the anchor drop tests, anchor the tests. Regarding to the water effect the power cable should be specified velocity is the most important factor on the mattress, it should be empha- to dissipate impact energy. A series of
FIGURE 10
Settlement depth (a) and damaged area (b) versus falling distance obtained from T1 to T4.
78 Marine Technology Society Journal field anchor drop and dragging tests was shown that soil composition did agency or its officers, agents, and will be scheduled to investigate the provide a representative effect on the employees. mechanism and accordingly to establish settlement depth and damaged area. a safety evaluation guideline of sub- Considering the settlement depth of marine power cable protection in the the soils, the damaged areas of the con- Corresponding Author: near future. The associated projects crete blocks, and the damaged state of Won-Bae Na in South Korea will be launched in the pipes (safety zone), all of the test Department of Ocean Engineering, 2013 and are expected to be done in results showed that the mattress failed Pukyong National University, 2015. to protect the power cable from the an- Busan, South Korea chor collision forces. The deformation, Email: [email protected] damage, and breakage of the pipe, sim- Conclusions ulating the safety zone of the power This study presents anchor drop cable, gave clues as to the failure. How- References tests on a newly designed matrix-type ever, it should be noted here that the Byrne, B.W., & Houlsby, G.T. 2012. submarine power-cable protector as- failure assessment in this study does Foundations for offshore wind turbines. sembled from reinforced concrete not necessarily ideally represent the Philos Trans R Soc A. 361:2909-30. http:// blocks to make a safety assessment. real failure of the power cables in the dx.doi.org/10.1098/rsta.2003.1286. For the study, the conditions of the target marine environment because of Coffen-Smout, S., & Herbert, G.J. 2000. marine environments, such as water real power cable specifications, such as fi Submarine cables: A challenge for ocean depths and soil speci cations, were the presence of armor layers. Also, in management. Mar Policy. 24:441-8. http:// surveyed at the target site and sim- the calculations of falling distances, a dx.doi.org/10.1016/S0308-597X(00)00027-0. ulated in the test set-up. A 2-ton conservative selection would result in stock anchor was selected as the collid- a worse failure assessment. Never- Daudeville, L., & Malécot, Y. 2011. Concrete ing object, a 25-ton crane was prepared theless, this study shows the collision structures under impact. Eur J Environ Civil Eng. 15:101-40. http://dx.doi.org/ to drop the anchor, and recording process of the stock anchor on the mat- 10.1080/19648189.2011.9695306. units were set up to capture the col- tress, damaged patterns of the concrete lision process and damage patterns. blocks, soil settlement, and effect of DNV-RP-F107. 2010. Risk Assessment of Before carrying out designated test sce- soil composition on the test results. Pipeline Protection. Katy, TX: Det Norske narios, preliminary tests were per- Thus, it was shown that the test pro- Veritas. formed to investigate the effects of cess and results provide valuable infor- DNV-RP-F401. 2012. Electrical Power Cables the soil composition and mattress ar- mation to design further anchor drop in Subsea Applications. Katy, TX: Det Norske rangement on the test results. Finally, tests, specify the soil conditions, and Veritas. four anchor drop test scenarios were establish a safety evaluation guideline Esteban, M.D., Diez, J.J., López, J.S., & designed, carried out, and analyzed, of submarine power cable protection Negro, V. 2011. Why offshore wind energy? and then a safety assessment was in the near future. Renew Energ. 36:444-50. http://dx.doi.org/ made for the matrix-type submarine 10.1016/j.renene.2010.07.009. power-cable protector. From the tests, in addition to the Acknowledgments Fox, R.W., McDonald, A.T., & Pritchard, P.J. falling distance, it was found that soil This study was supported finan- 2004. Introduction to Fluid Mechanics. Hoboken, NJ: Wiley. composition was a significant factor cially by the Singangjin Power Station in the settlement depth and damaged of the Korea Electric Power Corpora- International Cable Protection Committee. area. Case 2 (3% gravel and 97% tion (KEPCO). We sincerely thank 2009. Damage to submarine cables caused by sand) gave deeper settlement depths Dr. Hongjin Kim for his technical sup- anchors. Loss Prevention Bull. Available at: and wider damaged areas than Case 1 port. Additionally, material prepara- http://www.iscpc.org/publications/Loss_ (50% gravel and 50% sand) did. This tion by Samsung Industry is greatly Prevention_Bulletin_Anchor_Damage.pdf. observation was also made in the pre- appreciated. It should be noted here Jie, W., & Yao-Tian, F. 2012. Study on safety liminary tests; thus, in addition to the that this paper does not necessarily monitoring system for submarine power cable soil conditions (dry and saturated), it represent the views of the funding on the basis of AIS and radar technology.
May/June 2013 Volume 47 Number 3 79 Phys Proc. 24:961-5. http://dx.doi.org/ 10.1016/j.phpro.2012.02.144.
Kim, H.S., Kim, C.G., Na, W.B., Woo, J., & Kim, J.K. 2008. Physical and chemical deterioration of reinforced concrete reefs in Tongyeong coastal waters, Korea. Mar Technol Soc J. 42(3):110-8.
KS V3311. 2006. Anchor. Korean Standards Association.
Liu, F., Chen, G., Li, L., & Guo, Y. 2012. Study of impact performance of rubber reinforced concrete. Constr Build Mater. 36:604-16. http://dx.doi.org/10.1016/ j.conbuildmat.2012.06.014.
Sharples, M. 2011. Offshore electrical cable burial for wind farms: state of the art, standards and guidance & acceptable burial depths, separation distances and sand wave effect. Washington, DC: Bureau of Safety and Envi- ronmental Enforcement.
Wagner, E. 1995. Submarine cables and protections provided by the law of the sea. Mar Policy. 19:127-36. http://dx.doi.org/ 10.1016/0308-597X(94)00002-A.
Woo, J., Na, W.B., & Kim, H.T. 2009. Numerical simulation of arch-type submarine cable protector under anchor collision. J Ocean Eng Technol. 23:96-103.
Woo, J., & Na, W.B. 2010. Analyses of the maximum response of cylinders-connected protector under anchor colliding and dragging. J Ocean Eng Technol. 24:81-7.
Yamabuki, K., & Kubori, K. 2012. A tran- sient analysis of a scaled model for a sub- marine cable connected with an offshore wind farm. Electr Pow Syst Res. 85:59-63. http:// dx.doi.org/10.1016/j.epsr.2011.07.009.
80 Marine Technology Society Journal PAPER Elements of Underwater Glider Performance and Stability
AUTHORS ABSTRACT Shuangshuang Fan Underwater gliders are winged autonomous underwater vehicles (AUVs) that The State Key Lab of Fluid Power can be deployed for months at a time and travel thousands of kilometers. As Transmission and Control, with any vehicle, different applications impose different mission requirements Zhejiang University that impact vehicle design. We investigate the relationship between a glider’s Craig Woolsey geometry and its performance and stability characteristics. Because our aim is to Department of Aerospace and identify general trends rather than perform a detailed design optimization, we con- Ocean Engineering, Virginia Tech sider a generic glider shape: a cylindrical hull with trapezoidal wings. Geometric parameters of interest include the fineness ratio of the hull, the wing position and shape, and the position and size of the vertical stabilizer. We describe the 1. Introduction results of parametric studies for steady wings-level flight, both at minimum glide fl or at least two decades, experi- angle and at maximum horizontal speed, as well as for steady turning ight. We mental ocean scientists have envi- describe the variation in required lung capacity and maximum lift-to-drag ratio F corresponding to a given vehicle size and speed; we also consider range and en- sioned a dense distribution of mobile ocean sensor platforms to provide per- durance, given some initial supply of energy for propulsion. We investigate how the fi sistent and pervasive ocean monitoring turning performance varies with wing and vertical stabilizer con guration. To (Curtin et al., 1993). Within this vi- support this analysis, we consider the glider as an 8-degree-of-freedom multibody sion, there is an economic argument system (a rigid body with a cylindrically actuated internal moving mass) and fl for using underwater gliders to sample develop approximate expressions for turning ight in terms of geometry and control ’ the deep ocean over large spatial and parameters. Moving from performance to stability and recognizing that a glider s temporal scales (Rudnick et al., 2004). motion is well described in terms of small perturbations from wings-level equilib- fi fl The first generation of underwater rium, we study stability as an eigenvalue problem for a rigid (actuators- xed) ight gliders, such as Slocum (Webb et al., vehicle. We present a number of root locus plots in terms of various geometric param- 2001), Seaglider (Eriksen et al., 2001), eters that illuminate the design tradeoff between stability and control authority. and Spray (Sherman et al., 2001), were Keywords: multibody dynamics, design analysis, range and endurance, buoy- designed for such long-endurance, deep ancy propulsion ocean sampling missions. More recent development efforts have produced var- iants that are suitable for both deeper at Virginia Tech provides unique new was that a blended wing-body glider (Osse & Eriksen, 2007) and shallower capabilities for testing such algorithms would yield greater flight efficiency (Teledyne Webb Research, 2013) op- (Wolek et al., 2012). than “legacy” configurations. The pri- erations. Although glider endurance Earlier studies have addressed vari- mary focus of the 2003 glider study suffers in shallower water, it compares ous stability and performance tradeoffs was performance; earlier investigations well with that of conventional under- involved in underwater glider design. had considered stability. Graver et al. water vehicles, and gliders are more ro- A sweeping 2003 analysis sponsored (1998) investigated the stability of bust to biological fouling and debris. by the U.S. Office of Naval Research wings-level flight with respect to a Moreover, advanced perception, plan- provided insightful comparisons be- “bottom-heaviness” parameter related ning, and control algorithms that exploit tween the propulsive efficiency of un- to the glider’s metacentric height. natural vehicle and environmental dy- derwater gliders and both biological Galea (1999) provided a general static namics can improve performance. A and engineered flyers (Jenkins et al., stability analysis for glider wings-level shallow-water glider developed recently 2003). One conclusion of that study flight and turning motion. Graver
May/June 2013 Volume 47 Number 3 81 (2005) analyzed scaling rules for steady design optimization, we use simple and lateral-directional eigenmodes for glide performance (e.g., the glide speed methods such as these to develop a a rigid glider vary with certain geomet- versus ballast loading, glide angle and generic glider hydrodynamic model ric parameters. We summarize and glider volume), and he provided a that supports performance and stability conclude in Section 6. preliminary overview of glider design analysis. We consider two wings-level requirements, including sizing, body, flight conditions (minimum glide angle and wing geometry. Graver (2005) and maximum horizontal speed) as well 2. Underwater Glider also discussed longitudinal stability, as turning motion. To support our anal- focusing especially on the role of the ysis of turning motion for a vehicle Dynamics With a phugoid mode, a mode that had been with a cylindrically actuated internal Cylindrically Actuated recognized in aircraft motion a cen- moving mass, we follow the regular Moving Mass tury before by Lanchester (Lanchester, perturbation method described in The 8-degree-of-freedom glider is m 1908; Mises, 1959). Nonlinear gliding Mahmoudian et al. (2010). The per- modeledasarigidbody(mass rb) m stability is discussed in Bhatta and formance analysis covers preliminary with a single moving point mass ( p) Leonard (2008), where a composite design considerations, such as sizing, that is offset from the centerline. The Lyapunov function is constructed to range and endurance, and turning capa- point mass can move longitudinally prove gliding stability. One advantage bility. For stability analysis, we view the and can revolve around the vehicle cen- of Lyapunov analysis is that it pro- glider as a rigid body and investigate terline. Earlier multibody dynamic vides a tool for estimating the region the effect of geometric parameters on models incorporated one or more of attraction for asymptotically stable the longitudinal and lateral-directional rectilinear mass particles for attitude equilibria; such information can be eigenmodes. Specifically, we consider control, but the cylindrical actuation useful in scheduling transitions be- the effect of changes in wing shape, scheme better reflects the actual con- tween steady motions. wing longitudinal location, and verti- trol mechanism in several existing In any flight vehicle design effort, it cal stabilizer size and location. gliders. is important to understand the rela- In this paper, we consider a con- The vehicle also includes a variable tionship between vehicle geometry ventional glider configuration compris- ballast actuator whose effect is repre- m and performance and stability (Pamadi, ing a cylindrical hull with a trapezoidal sented by a point mass ( b) with vari- fi 2004). To simplify our parametric anal- wing and vertical stabilizer. The anal- able volume (Vb), which is xed at the ysis, we describe the hull and wing ysis makes use of a new multibody body frame origin. In modeling a buoy- geometry using several nondimen- dynamic model for a glider with a cy- ancy control system, one may assume sional parameters: the hull fineness lindrically actuated moving mass. This either that the mass varies or the dis- ratio, wing aspect ratio, wingspan actuation scheme matches that of sev- placement, depending on whether the ratio, and wing thickness ratio. In ad- eral existing gliders including Seaglider, “control volume” that contains the dition to these parameters, the wing Spray, and the Virginia Tech underwater vehicle is fixed or deformable. In either and vertical stabilizer configurations glider (Wolek et al., 2012). The paper case, the net effect is a change in the (shape, size, and location) are also con- is organized as follows. Section 2 pre- vehicle’s density. Thus, in our model, sidered. As hydrodynamic coefficients sents the derivation of an 8-degree- when the variable ballast actuator de- are determined by the glider geometry of-freedom underwater glider dynamic creases the vehicle’svolumesufficiently, and the flow characteristics, it is neces- model with a cylindrically actuated the vehicle becomes denser than the sary to obtain a hydrodynamic model moving mass. In Section 3, we define surrounding water and descends. Con- for the glider. For generic vehicle the nomenclature associated with glid- versely, when the actuator increases the shapes, there are well-known semi- er geometry and with vehicle motion displaced volume, the vehicle becomes empirical expressions relating geometry and we review relevant glider hydrody- less dense than the surrounding water to aerodynamic (or hydrodynamic) coef- namic characteristics. Section 4 presents and ascends. ficients (Etkin & Reid, 1996; USAF some analytical results concerning per- The total vehicle mass, which Stability and Control DATCOM). formance in steady wings-level flight remains fixed, is Because our focus is to identify general and in steady turning motion. Sec- trends rather than perform a detailed tion 5 describes how the longitudinal m ¼ mrb þ mp þ mb
82 Marine Technology Society Journal 2.1. Kinematics (roll angle φ, pitch angle θ, and head- In addition to the 6 degrees of free- Define a body-fixed, orthonormal ing angle ψ), we have dom associated with the vehicle’strans- reference frame centered at the geo- lation and rotation, there are 2 degrees e^ ψ e^ θ e^ φ metric center of the vehicle (the cen- RIBðÞ¼φ; θ; ψ e 3 e 2 e 1 of freedom associated with the moving ter of buoyancy) and represented by mass, which is modeled as a particle. To where e (·) denotes the matrix the unit vectors b1, b2,andb3.The describe the point mass position, we de- exponential. fi “ ” vector b1 is aligned with the longi- ne a third orthonormal actuator triad tudinal axis of the vehicle, b points The origin of the body frame sits at {a , a , aμ}, where a is parallel with b 2 ’ 1 r 1 1 out the right wing, and b completes the vehicle s center of buoyancy (CB), (see Figure 1). The vector a points in 3 fi r the right-handed triad (see Figure 1). which remains xed under our as- the radial direction from the vehicle Define another orthonormal reference sumptions. The center of mass (CM) centerline through the point mass. The frame, denoted by the unit vectors i , of the glider (neglecting the contri- vector aμ completes the right-handed 1 m fi bution of p) is located at rrb (see i2,andi3,whichis xed in inertial frame. The proper rotation matrix RBP space such that i is aligned with the Figure 1). Let the inertial vector X = maps free vectors from this particle- 3 x y z T force due to gravity. The relative orien- [ , , ] represent the position vector fixed frame to the body frame, tation of these two reference frames is from the origin of the inertial frame to 0 1 the origin of the body frame. Let v = 10 0 given by the proper rotation matrix T T @ A u v w ω p q r RBP ¼ sinμ cosμ R , which maps free vectors from [ , , ] and =[ , , ] represent 0 IB 0 cosμ sinμ the body-fixed reference frame into the translational and rotational veloci- the inertial reference frame. Let ei ty of the body with respect to the iner- where μ is the rotation angle of the represent the standard basis vector tial frame, but expressed in the body moving mass about the longitudinal for R3, where i Î{1, 2, 3}, and let the frame. The kinematic equations are axis of the vehicle. Let character ^ denote the 3 × 3 skew- X ¼ RIBv ð1Þ 0 1 symmetric matrix satisfying ab^ ¼ r px a b ∼ ¼ r þ R ¼ @ R A × for vectors a and b.Then,in rp pxa1 par p ^ RIB¼ RIBω ð2Þ terms of conventional Euler angles 0 p
denote the particle’s position with re- spect to the body frame origin, expressed FIGURE 1 in the particle frame. Correspondingly, An underwater glider with a cylindrically actuated moving point mass. define the body vector 0 1 r px ∼ @ A rp ¼ RBPrp¼ Rp sinμ Rp cosμ b
Then the kinematics of the moving mass particle relative to inertial space is ¼ þ ω þ μ Þ þ ÞðÞ vp v b1 × rp rpxb1 3
Note that we may also write ¼ I ^ ^ η vp r p e1! rpe1 v ω where η ¼ : rpx μ
May/June 2013 Volume 47 Number 3 83 2.2. Dynamics where cylindrical fuselage has diameter d and To derive the equations of motion, length l. The wingspan (tip to tip) is b. fi fi T one rst de nes the total kinetic energy ζ ¼ R i3 We consider an untapered, trapezoidal of the body/particle/fluid system, wing with a constant cross-sectional is the “tilt vector,” the body frame unit shape. The wing planform area is de- S 1 T vector in the direction of gravity, fv noted . The mean aerodynamic chord T ¼ Tp þ Tb þ Trb þ Tf ¼ η M rp η 2 and mv are the viscous force and mo- length (i.e., the average width of a rect- ment acting on the glider, expressed angular wing with equivalent aerody- where u τ namic properties) is c and S ¼ b⋅c. in the body frame, and px and px are the input force and moment, which Another important geometric param- M ¼ M þ M þ M þ M t rp p rp b rb f adjust the moving point mass location eter is the maximum wing thickness . to control vehicle attitude. The hull and wing geometry can be u Explicit expressions for the generalized Letting b denote the rate of change characterized by several nondimen- inertia matrices are given in Appendix A. of displaced volume, an input, we have sional parameters: the hull fineness The generalized momentum is ratio ( f ), the wing aspect ratio (AR), κ Vb ¼ u ð Þ the wingspan ratio ( ), and wing thick- 0 1 b 8 ∼ p ness ratio (t ). B C ∂T B h C ¼ Equations (4) through (8) describe the @ p A ∂η px l b2 b h dynamics of the cylindrically actuated f ¼ ; AR ¼ ; κ ¼ ; and px glider. Together with the kinematic d S d t equations (1), (2), and (3), these equa- t∼ ¼ where p is the total body translational c tions completely describe the motion momentum, h is the total body an- of the vehicle in still water. gular momentum, and p and h ap- px px Having obtained a multibody dy- We also consider a few other con- pear in the point mass momentum as fi namic model, one may compute steady guration parameters for the wing follows: motions, examine their stability, de- and vertical stabilizer, including wing l 0 1 velop feedback control schemes, and longitudinal position w, vertical stabi- pp lizer longitudinal position lv and area @ x A implement them in simulation. For p ¼ RBP pp S p r example, one may investigate flight of the vertical stabilizer v. The aerody- hp =Rp x p control methods that involve stitch- namic center of the wing and the ver- tical stabilizer, which is located near ing together sequences of stable glid- ∼ ∼ l l The dynamic equations in the body ing motions, as in Mahmoudian and the quarter-chord line, are w and v l frame are Woolsey (2013). (normalized by the fuselage length ) aft of the center of buoyancy, respec- ¼ ω þ ∼ ζ þ ð Þ p p × mg fv 4 tively, while the area of the vertical sta- S bilizer v is normalized by the fuselage ¼ ω þ þ m g ζ h h × p × v rb rrb × 3. Glider Geometry frontal area Sf .Allofthegeometric and Hydrodynamic þ mpgrp × ζ þ mv ð5Þ parameters that we consider are indi- Characteristics cated in Figure 2. 3.1. Geometry and Nomenclature A critical parameter for perfor- p ¼ ⋅ T ω þ μ Motivated by the challenge of de- mance analysis is the buoyant lung px e1 RBP pp × b1 capacity η signinganunderwaterglidertomeet , given as a percentage of þ m gζ þ u ð Þ p px 6 particular mission requirements, we the neutrally buoyant displacement. investigate the general relationship be- Buoyancy actuators include piston- tween glider geometry and the stability cylinder arrangements, oil-filled blad- T hp ¼ Rpe ⋅ R p ω þ μb x 3 BP p × 1 and performance characteristics. In ders, and pneumatic bladders. For doing so, we consider a generic wing- simplicity, we consider the case of a þ mpgζ þ τp ð7Þ x and-cylinder configuration, where the piston-cylinder actuator and assume a
84 Marine Technology Society Journal FIGURE 2 The hydrodynamic force and moment Geometric parameters of the underwater glider model. are typically represented using non- dimensional coefficients as follows: 0 1 0 1 L CL @ A 1 2 @ A fv ¼ RBC SF ¼ ρV S CSF 2 D CD 0 1 0 1 K bCl @ A 1 2 @ A mv ¼ M ¼ ρV S cCm 2 N bCn
The nondimensional coefficients de- pend on the vehicle geometry and the flight condition. Based on physical considerations, such as left/right sym- metry of the outer mold line, we assume cylindrical hull with constant cross- Let η denote the fractional dis- these coefficients have the following sectional area (see Figure 3). Recall placement from neutral buoyancy, dependencies that the dynamic model presented ear- η ∈ η; η ,defined such that η >0 C ¼ C α; q∼ ; C ¼ C β; p∼; r∼ ; lier assumes changes in buoyant vol- corresponds to an increase in buoy- L L SF SF umeoccurattheoriginofthebody ancy. Then ∼ ∼ ∼ frame. Although a change in buoyancy CD ¼ CD α; q ; Cl ¼ Cl β; p; r ; generated with the arrangement shown B ¼ ρgðÞ1 þ η VNB in Figure 3 would induce a moment, C ¼ C α; q∼ and C ¼ C β; p∼; r∼ we do not account for it here; our aim Thus, m m n n is merely to relate changes in buoyancy η ∼ p∼; q∼; r∼ to the vehicle geometry. Let denote W ¼ W B ¼ ρgVNB ρgðÞ1 þ η VNB Here, are nondimensional roll, the percentage difference between the pitch and yaw rates, which are defined ¼ ηρgVNB displacement required for neutral buoy- as η ancy (VNB) and the maximum displace- ¼ ρgV þ η ∼ ∼ ment (V). That is, 1 p ¼ p=ðÞ2V0=b ; q ¼ q= 2V0=c
∼ V ¼ð1 þ ηÞVNB and η ¼ V=VNB 1 and r ¼ r=ðÞ2V =b 3.2. Hydrodynamic Characteristics 0 To assess glider performance and V where V = W/(ρg)andW is the where 0 is the nominal velocity of the NB stability, it is necessary to develop a vehicle’s dry weight. The “net weight” vehicle. (Please note that while V rep- ∼ hydrodynamic model. The hydro- of the glider is denoted W ¼ W B, resents volume, V represents speed.) B dynamic forces (lift, side force, and drag) For aircraft flight dynamic models, de- where is the buoyant force. “ ” are expressed in the current reference pendence of the forces and moments fi FIGURE 3 frame, de ned such that the 1-axis is on vehicle acceleration is typically in- α aligned with the velocity vector. Let = cluded in these nondimensional coeffi- Notional schematic of the buoyancy actuation arctan(w/u) denote the vehicle’s “angle cients as well (e.g., dependence of Cm system. ” β v of attack and let =arcsin(/||v||) on α). Here, these effects are instead “ ” denote the sideslip angle. The cur- included in the added mass and inertia rent frame is related to the body frame terms. Dependence of the moments through the proper rotation matrix on inertial attitude, due to the meta- centric moment, is also incorporated e^ α e^ β RBCðÞ¼α; β e 2 e 3 elsewhere in the formulation.
May/June 2013 Volume 47 Number 3 85 Following convention, we assume hull diameter, or wing chord). In fact, coefficients CL and CD. The coefficients that the nondimensional hydrodynamic the hydrodynamic coefficients are espe- CL and CD are related to the descent angle forces and moments above depend cially sensitive to Reynolds number for ξ as shown in the triangle at the right in linearly on their arguments (e.g., Cn ¼ speeds at which underwater gliders Figure 4. Summing forces in Figure 4 C β þ C p∼ þ C r∼ nβ np nr ), with the excep- typically operate. For motion through along the velocity direction gives tion of the drag coefficient, which var- water, these speeds correspond to a crit- ies quadratically with lift, ical Reynolds number range in which ∼ 1 2 fl CD ρV S ¼ W sin ξ ow over the vehicle may (or may not) 2 C ¼ C þ KC 2 D D0 L transition from laminar to turbulent. The descent angle is the angle from the CD The parameter 0 represents the par- inertial horizontal plane down to the ve- asitic drag due, for example, to skin fric- 4. Performance Analysis locity vector; it is the negative of the K tion. The parameter accounts for drag 4.1. Steady Motions flight path angle γ that is commonly that is induced when the wing gener- In this section, we discuss two types used in aircraft flight dynamics (Etkin ates lift. It scales inversely with the of underwater glider steady motions: & Reid, 1996). Solving for speed, one AR aspect ratio ; induced drag vanishes wings-level flight and steady turning finds that for a wing of infinite span. motion. sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi fi ∼ The hydrodynamic coef cients (such W sin ξ C V ¼ 2 ð Þ as nβ ) are determined in part by the 9 4.1.1. Wings-Level Flight ρSCD glider geometry, such as the slender- Our discussion of wings-level per- ness of the fuselage, the shape and formance begins with a general over- location of the wing, the size and loca- The horizontal and vertical components view and then focuses on two specific tion of the vertical stabilizer, etc. For of speed are flight conditions: flight at minimum generic flight vehicle shapes, there are glide angle and flight at maximum Vx ¼ V cosξ well-known semiempirical expressions horizontal speed. relating geometry to aerodynamic (or Figure 4 shows the free body dia- Vz ¼ V sin ξ hydrodynamic) coefficients (Etkin & gram for a flight vehicle in wings- Reid, 1996; USAF Stability and Control ∼ level gliding flight. In this sketch, W DATCOM), although these methods Referring to Figure 4, we note the fol- denotes the vehicle’s net weight (weight are imprecise. One can obtain higher lowing relationships: fi minus buoyant force). Here, we adopt delity approximations using compu- “ ”— fl a performance model we treat the CD tational uid dynamics methods, rang- sin ξ ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi and vehicle as a point mass, ignoring rota- C 2 þ C 2 ing from simple vortex lattice methods D L tional dynamics. As explained earlier, to full Navier-Stokes solvers. However, CL the lift and drag force are typically ex- cos ξ ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð10Þ semiempirical methods provide a sim- C 2 þ C 2 pressed in terms of nondimensional D L ple way to investigate the first-order effect of changes in vehicle geometry FIGURE 4 on performance and stability. While hydrodynamic coefficients Free body diagram for wings-level gliding flight. depend on glider geometry, they also depend on the flow characteristics, which correlate to the Reynolds number
Vx ¼ length Re ν where xlength is some characteristic lin- ear dimension (e.g., vehicle length,
86 Marine Technology Society Journal Recall that at a constant altitude), this flight condition corresponds to the minimum drag force; the values of the drag and lift coefficient in this condition are ∼ η W ¼ ρgV 1 þ η rffiffiffiffiffiffiffiffi CD C ¼ C and C ¼ 0 Dmd 2 D Lmd 0 K As mentioned earlier, we assume that buoyancy is controlled by a single- “ ” “ ” stroke (piston-cylinder) actuator. We (Adopting aircraft nomenclature, the subscript md stands for minimum drag. ) ξ take the piston diameter to be the hull These expressions can be obtained by differentiating the right-hand side of tan = 2 CD KCL CL CL fi diameter, and we assume the buoyancy ( 0 + )/ with respect to and nding the roots. Referring to equation (12), fi “ fl ” actuation is concentrated at the origin we nd that the speed for minimum drag (the speed-to- y )is of the body frame (i.e., we ignore mo- vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi u , ments due to changes in buoyancy). u qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi tπgl AR η When the vehicle’s net weight is maxi- Vmd ¼ C 2 þ C 2 κ2 þ η Dmd Lmd mum, we have η ¼ η so that 2 1 vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð13Þ u ,rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi uπgl AR η C ∼ η t D ¼ 0 ðÞ1 þ 4KCD W ¼ ρgV κ2 þ η K 0 1 þ η 2 1 η π ¼ ρg d 2l ð Þ þ η 11 1 4 The minimum glide angle condition is illustrated in the plot of CL versus CD in Figure 5, a curve sometimes called the drag polar. Note that the lift-to-drag ratio is Substituting equation (11) into equa- maximum when a line extending from the origin is just tangent the drag polar. tion (9), we find that This flight condition corresponds to the shallowest achievable glide angle, which is 8° in the case of the Slocum model given in (Graver, 2005; Bhatta, 2006). ∼ B. Maximum Horizontal Speed. 2W sinξ Using the lift-and-drag triangle in Figure 4, we V 2 ¼ fi ρSCD nd that πgl d 2 η sinξ ¼ sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ∼ 2 S 1 þ η CD W C V ¼ 2 L x = πgl AR η ρS ½ C 2 þ C 2 3 4 ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1 L D κ2 þ η 2 2 2 1 CD þ CL ð Þ 12 FIGURE 5
Slocum Thus, we find that speed scales with Drag polar for a model of the glider. the square root of linear dimension l and inversely with the wingspan ratio κ. The dependence of speed on aspect ratio is more subtle, since AR affects CD through the induced drag parameter K. A. Minimum Glide Angle Flight. In still water, flight at the shallowest glide path angle results in the maximum horizontal range. Referring to Figure 4, the minimum glide angle occurs when the lift-to-drag ratio is maximum. In powered flight (e.g., for aircraft flying
May/June 2013 Volume 47 Number 3 87 pffiffiffi The value is maximum when by its theoretical limit arctan 1= 2 . Further, one may verify that in the KC → C limit D0 0, the lift and drag fCðÞ¼ L L = fi 2 2 3 4 coef cients for maximum horizontal ½ CL þ CD speed are
fi σ ¼ KC fi pffiffiffi is maximum. De ning 2 D0 , one nds (after some effort) that C ≈ C and LmaxVx 2 D0
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi CD V ≈ CD ðÞþ KCD rffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi max x 0 1 2 0 2 C ¼ ðÞþþ σ ðÞþ σ 2 þ σ2 LmaxVx 1 1 8 4K qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4.1.2. Turning Motion 1 C ¼ C þ ðÞþþ σ ðÞþ σ 2 þ σ2 DmaxVx D 1 1 8 Mahmoudian et al. (2010) devel- 0 K 8 oped analytical approximations for steady turning motion of an under- Noting from Figure 4 that water glider using regular perturbation theory, with the vehicle turn rate as the C perturbation parameter. The analysis tan ξ ¼ D ; CL assumed rectilinear motion of the mov- ing point mass. Using the same ap- proach, we rederive the steady turning we find that for wings-level gliding flight at maximum horizontal speed, flight approximation with a cylindrical qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi moving point mass actuator. We treat pffiffiffi 1 fl σ þ pffiffiffi ðÞþþ σ ðÞþ σ 2 þ σ2 turning ight as a small perturbation C 2 1 1 8 tan ξ ¼ DmaxVx ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi8 from a nominal, wings-level equilibrium C qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi LmaxVx fl V ðÞþþ σ ðÞþ σ 2 þ σ2 ight condition at speed 0 and pitch 1 1 8 θ angle 0, at some corresponding angle α fl of attack 0. In wings-level ight, the μ Figure 6 shows the drag-to-lift ratiopffiffiffi and the descent angle. Note that in the limit moving mass rotation angle =0,so σ → 0, we have ξ → arctan 1= 2 ≈ 35°. that the roll angle ϕ and the sideslip fl KC β For well-designed ight vehicles, for which the product D0 is reasonably angle are both zero. We hold the θ small, the descent angle for maximum downrange speed is well approximated pitch angle constant at 0 and perturb the steady wings-level flight such that the body angular velocity vector ω is FIGURE 6 vertical with a small magnitude ɛωn KC ωn Drag-to-lift ratio and descent angle versus 2 D0 . where is somepffiffiffiffiffiffiffi characteristic fre- g=l V l ɛ quency (e.g., or 0/ ), and is the perturbation parameter. To first order in ɛ, one finds
V ≈ V ; φ ≈ ɛφ ; 0 1
α ≈ α ; β ≈ ɛβ ; 0 1
m∼ ≈ m∼ and μ ≈ ɛμ 0 1
φ β Explicit expressions for 1, 1,and μ 1 are given in equations (14), (15),
88 Marine Technology Society Journal and (16); these analytical expressions enable one to investigate the role of vehicle parameters in a vehicle’sturning performance. ∼ ∼ ∼ ξ ¼ gm m R ÞÞV ω C l 2m Sρ þ m N þ m r m X cosα cotθ 1 1 2 p 0 p 0 n nr 0 2 0 v p p u 0 0 x ∼ ∼ m M þ m r m þ Z sinα S Cn lm þ m r CD þ CS þ C 2 K α2 ρ 2 0 w p p w 0 β 0 p p 0 β Lα 0 x x ∼ ∼ ∼ þ m X þ Y Þcos α Þcscθ C l 2m Sρ þ m N þ m r m X cos α Þcosθ2 2 0 u v 0 0 nr 0 2 0 v p p u 0 0 x ∼ 2 þ Cl l 2m Sρ þ m r þ m R ðÞm Z sinα Þsinθ þ m r þ m R m X cos α p 0 2 rb rbz p p w 0 0 rb rbz p p u 0 ∼ ∼ þ m N þ m r m Z sinα sin θ S Cn lm þm r CD þ CS þ C 2 K α2 ρ 0 v p p w 0 2 0 β 0 p p 0 β Lα 0 x x ∼ ∼ þ m X þ Y cos α cos θ þ S Cl lm þ m r þ m R CD þ CS þ C 2 K α2 ρ 2 0 u v 0 0 β 0 rb rbz p p 0 β Lα 0 ∼ þ 2m0 Yv Zw sinα0 sinθ0 ð14Þ
∼ ∼ ∼ φ ¼ = gm V ω secθ m þ m X cos α cosθ þ m þ m Z sinα sinθ 1 1 2 0 0 n 0 2 0 u 0 0 2 0 w 0 0 ∼ ∼ 2 S CD þ CS þ C 2 K α2 ρ Cn l 2m Sρ þ m N þ m r m X cos α cosθ 0 β Lα 0 r 0 2 0 v p p u 0 0 x ∼ 2 þ Cl l 2m Sρ þ m r þ m R m Z sinα sinθ þ m r þ m R m X cosα p 0 2 rb rbz p p w 0 0 rb rbz p p u 0 ∼ ∼ þ m N þm r m Z sinα sin θ = S Cn lm þ m r CD þCS þC 2 K α2 ρ 0 v p p w 0 2 0 β 0 p p 0 β Lα 0 x x ∼ ∼ þ m X þ Y cos α cosθ þ S Cl lm þ m r þ m R CD þ CS þ C 2 K α2 ρ 2 0 u v 0 0 β 0 rb rbz p p 0 β Lα 0 ∼ þ 2m0 Yv Zw sinα0 sinθ0 ð15Þ
∼ ∼ β ¼ ω C l 2m Sρ þ m N þ m r m X cos α cosθ2 1 n nr 0 2 0 v p p u 0 0 x ∼ 2 þ Cl l 2m Sρ þ m r þ m R m Z sinα sinθ þ m r þ m R m X cosα p 0 2 rb rbz p p w 0 0 rb rbz p p u 0 ∼ ∼ þ m N þ m r m Z sinα sin θ = V S Cn lm þ m r CD þCS þC 2 K α2 ρ 0 v p p w 0 2 0 0 β 0 p p 0 β Lα 0 x x ∼ ∼ þ m X þY cosα cos θ þ S Cl lm þ m r þ m R CD þ CS þ C 2 K α2 ρ 2 0 u v 0 0 β 0 rb rbz p p 0 β Lα 0 ∼ þ 2m0 Yu Zw sinα0 sinθ0 ð16Þ
4.2. Parametric Performance Analysis Here, we examine performance in steady wings-level and turning flight.
4.2.1. Performance Analysis of Wings-level Flight A vehicle’s geometry defines its performance. We first consider the effect of various geometric parameters on the speed at minimum glide angle (also called the “speed to fly”) and the maximum lift-to-drag ratio. We also consider range, endurance, and number of dives, for a given propulsive energy budget. We focus on a few key parameters such as hull length and fineness ratio, wing aspect ratio, the wingspan ratio, and also the buoyant lung capacity η. Size Analysis. Because underwater gliders operate at conditions where the flow over the vehicle and its components may be laminar or turbulent, it is important to keep track of the Reynolds number, which characterizes the flow over a body. We define
Vl Vc c κ Re ¼ and Re ¼ ¼ Re ¼ Re l ν c ν l l l fAR
May/June 2013 Volume 47 Number 3 89 Referring to equation (12), we may write Referring to (Hoerner, 1965; Stengel, 2004), one finds that CD depends on 0 2 C l πgl AR η Reynolds number, so D0 varies with 2 1 Rel ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ν κ2 þ η 2 2 speed and length. 2 1 CD þ CL Figures 7 and 8 present surface fi C plots of the variation in required lung Note that the Reynolds number Rel affects the parasitic drag coef cient D0 and thus appears on both sides of the equation above. Solving for η we find capacity and the maximum lift-to-drag ratio for a glider with the following parameter values 1 1 π gl 3 AR 1 η ¼ where Φ ¼ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð17Þ Φ Re2 ν2 κ2 2 2 1 l 2 CD þ CL l ¼ 1:5m; AR ¼ 11; κ ¼ 6;
∼ For flight at the shallowest descent angle, the parameters CD, CL,andRel are f ¼ 7; and t ¼ 0:02
rffiffiffiffiffiffiffiffi These parameter values are based on a CD Vmdl Slocum C ¼ C ; C ¼ 0 and Re ¼ : model of used in earlier studies Dmd 2 D Lmd lmd 0 K ν (Graver, 2005; Bhatta, 2006). Figure 7 shows the variation in lung fl The maximum lift-to-drag ratio at this ight condition can be described as capacity required for flight of a 52-kg sffiffiffiffiffiffiffiffiffiffiffiffiffi glider over a range of minimum glide L C angle speeds, given variations in one of ¼ Lmd ¼ 1 D C KC l AR Dmd 4 D0 the four geometric parameters , , κ,orf. (In each plot, the nonvarying FIGURE 7 parameters take the nominal values given earlier.) To reduce the lung ca- Variation of the required lung capacity with the given minimum glide angle speed and size. pacity required for a given speed at the (a) Variation of lung capacity with V and l. (b) Variation of lung capacity with V and AR. md md minimum glide angle, one should in- (c) Variation of lung capacity with Vmd and κ. (d) Variation of lung capacity with Vmd and f. crease the vehicle size (parameterized by hull length l )andfineness ratio f, and decrease the wingspan ratio κ.The required lung capacity does not vary with the wing aspect ratio AR. Figure 8 shows the variation in maximum lift-to-drag ratio of a 52-kg glider over a range of minimum glide angle speeds, given variations in one of the four geometric parameters l, AR, κ,orf.(Again,thenonvarying parameters take the nominal values given earlier.) The apparent disconti- nuities occur when the flow over the wings transitions between laminar and turbulent. To increase the lift-to-drag ratio for a given speed to flywithina given flow regime (laminar or turbulent), one should increase the vehicle size (i.e., the hull length l ) and the wing- span ratio κ. The lift-to-drag ratio ap- pears less sensitive to changes in hull
90 Marine Technology Society Journal FIGURE 8 the vehicle displacement varies from minimum to maximum Variation of maximum lift-drag ratio with the given minimum glide angle speed and size. (a) Vari- ation of maximum lift-to-drag ratio with Vmd and l. (b) Variation of maximum lift-to-drag ratio with η V AR V κ 2ηVNB ¼ 2 V md and . (c) Variation of maximum lift-to-drag ratio with md and . (d) Variation of maximum 1 þ η lift-to-drag ratio with Vmd and f. Correspondingly, the piston of the buoyancy actuator is moved from its maximally retracted position to its max- imally extended position. The piston must counter a hydrostatic pressure ρgΔz acting on the piston face, which has area πd2/4. Thus, we find that π η l 3 ΔE ¼ ρgΔz 2 1þ η f 2
In keeping with other simplifying as- sumptions, we ignore the variation in pressure within the dry volume due to the piston displacements. The time re- quired to execute this dive, assuming the symmetrical flight condition in ascent, is Δz ΔT ¼ 2 z
where, recalling equations (10) and (13), z ¼ Vmd sin ξmd sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi πgl AR η C ¼ Dmd fi = neness ratio or wing aspect ratio, depth. The energy required to execute κ2 þ η 2 2 3 4 2 1 CD þ CL within a given flow regime. asinglesaw-toothdiveisgiven(ap- md md Figure 9 shows the variation in proximately) by the pressure-volume Given an amount of stored energy E displaced mass (for neutral buoyancy) work required at depth. Assume that p allocated for propulsion, the total with length, for the nondimensional parameter values above. FIGURE 9 Range and Endurance. Referring to Neutral displacement versus length, at f =7. Figure 4 and considering saw-tooth profiles to a depth Δz at the minimum glide angle flight condition, the per-dive range is approximately
CL Δz Δx ¼ 2 md Δz ¼ pffiffiffiffiffiffiffiffiffiffiffi CD KC md D0
Note that we are ignoring the effects of transition between gliding flight con- ditions, on the assumption that such transitions can be effected quickly com- pared with the total dive time and
May/June 2013 Volume 47 Number 3 91 number of dives that can be executed to for propulsion is 540 kJ, equivalent Moreover, for deep dives, variation in depth Δz is toasingle5Ah,30VDCbattery. water density is significant (Osse & In generating Figure 10, we assumed Eriksen, 2007); ocean stratification E N ¼ floor p flight at the minimum glide angle and hull compressibility have a marked ΔE speed with the net weight (or buoy- effect on glider performance (Jenkins ancy) fixed at the maximum value, as et al., 2003). Considering these and where “floor” indicates the greatest determined from equation (17). other factors, such as the time spent lower integer. The total range that can As indicated in Figure 10(a), the in transition between equilibrium flight be traversed (in still water) is number of dives that can be executed conditions, would alter the range and R ¼ N Δx involves a tradeoff between nomi- endurance contours, but the qualitative nal speed and dive depth. Range and trends would persist. and the total endurance is endurance diminish nonlinearly with E ¼ N ΔT : increasing nominal speed but are inde- 4.2.2. Performance Analysis pendent of dive depth, a consequence of Turning Motion Figure 10 shows contour plots indi- of our assumptions that hydrostatic Based on the approximate expres- cating range and endurance and num- pressure is linear in depth (i.e., the sions of turning motion presented in ber of dives for a glider of given size water density is constant) and that Section 4.1.2, we examine how the and geometry when repeatedly diving pump efficiency does not vary with wing geometry (sweep angle, dihedral to a given depth at a given nominal depth. Deep diving gliders typically angle, and vertical placement) and speed. In these plots, the vehicle length modulate their buoyancy using a the vertical stabilizer geometry (location is 1.5 m, which corresponds to a mass pump-driven, oil-filled bladder whose lv and area Sv) affect turning capabil- of 52 kg. The total power available efficiency varies with ambient pressure. ity here. Variations in the wing sweep angle, dihedral angle, and vertical place- FIGURE 10 ment affect the roll moment due to sideslip, as expressed by the hydrody- Contours of range (in km), endurance (in days), and number of dives for a 540-kJ glider. (a) Dive fi C namic coef cient lβ (Etkin & Reid, contours. (b) Range contours (km). (c) Endurance contours (days). 1996). Therefore, we vary the coef- fi C cient lβ to investigate the effect of wing configuration parameters on turn- ing motion. Note that the vertical sta- bilizer parameters lv and Sv do not appear explicitly in equations (14), (15), and (16). However, they do affect the fi C hydrodynamic coef cients, such as Sβ , C C nr and nβ (Nelson, 1998) and thus influence turning performance. Recalling that turning motions are parameterized by the moving mass ro- tation angle (μ), the glider roll angle (φ), and the sideslip angle (β), we ex- amine the variation in the first-order μ φ β l S sensitivities 1, 1,and 1 with v, v, C and lβ for a given turn rate. Recall that approximate values of μ, φ,and β may be obtained by multiplying the μ φ β parameters 1, 1, and 1 by the turn rate. In Figures 12(a), 11(b), and 11(c), which were generated using expressions
92 Marine Technology Society Journal FIGURE 11 Linearizing the dynamic equations about μ ϕ β l S C Variation in turning parameters 1, 1 and 1 with v, v and l β . (a) Variation of turning parameters the above wings-level equilibrium, one l S C with v. (b) Variation of turning parameters with v. (c) Variation of turning parameters with l β. finds that the resulting equations de- compose into longitudinal and lateral- directional components. Ignoring certain kinematic variables, one obtains two sets of four, first-order equations,
Xlong ¼ Along Xlong þ Blong ulong and
Xlat ¼ Alat Xlat þ Blat ulat
where
T Xlong ¼ Δu; Δw; Δq; Δθ and
T Xlat ¼ ½ Δv; Δp; Δr; Δφ
and where the elements of the state and input matrices depend on the steady flight condition and on the glider geometry, through the stability derivatives. Eigenvalues λ and non- dimensional eigenvectors ν (in am- plitudeandphaseform)forthestate matrices Along and Alat are listed in l (14), (15), and (16), we see that when v examine the effects of a few critical Tables 1 and 2. S “ or v (or their product, the vertical sta- parameters on glider stability. For the maximum horizontal- bilizer volume”) is small and/or the di- speed flight condition considered C hedral parameter lβ is less negative, a here, the longitudinal eigenvalues smaller moving mass rotation μ and 5.1. Eigenmode Analysis shown in Table 1 include two real roll angle φ are required to establish Considering a glider with fixed ac- eigenvalues and a complex conjugate a given steady turn rate. Correspond- tuators as a rigid body, we linearize pair. Examination of the eigenvec- ingly, however, the vehicle’ssteadyturn the dynamic equations about a wings- tors associated with these eigenvalues rate is more sensitive to errors in the level equilibrium condition. Specifically, indicates the following character- rollangle.WhileFigure11describes we consider the case of steady flight at istic modes: the effect of wing and vertical stabilizer maximum horizontal speed. Given a ■ a quickly converging pitch rate geometry on the steady turning flight dynamic model, one may obtain an mode, condition, it says nothing of stability, equilibrium flight condition with the ■ aslowlyconvergingspeedmode, which is the topic of Section 5. help of a numerical trim solver. In our and case, using Matlab’s fsolve subroutine, ■ an underdamped mode in which we found the following equilibrium: the pitch angle is coupled with the 5. Stability Analysis angle of attack. ’ ∼ A glider s geometry affects the hy- Veq ¼ 0:77 m=s; meq ¼ 0:2130 kg; The lateral-directional eigenvalues drodynamic coefficients that appear shown in Table 2 also include two in stability analysis. In this section, γeq ¼ 35°; rpxeq ¼ 0:2826 m and real eigenvalues and a complex conju- we consider the natural modes of glider gate pair. Examination of the eigenvec- α ¼ : motion and use root locus analysis to eq 1 2° tors associated with these eigenvalues
May/June 2013 Volume 47 Number 3 93 TABLE 1
Eigenvalues and eigenvectors of longitudinal motion.
Longitudinal λ1 ¼ 3:28 λ3 ¼ 0:85 þ 0:27i λ3 ¼ 0:85 0:27i λ4 ¼ 0:06
Δu ν11 ¼ 0:0315∠0° ν21 ¼ 0:0661∠ 126° ν31 ¼ 0:0661∠126° ν41 ¼ 1∠0°
Δw ν12 ¼ 0:0631∠0° ν22 ¼ 0:6694∠0° ν32 ¼ 0:6694∠0° ν42 ¼ 0:0231∠180°
Δq ν13 ¼ 1∠180° ν23 ¼ 1∠84:5° ν33 ¼ 1∠ 84:5° ν43 ¼ 0:0005∠180°
Δθ ν14 ¼ 0:1306∠0° ν24 ¼ 0:4793∠ 78° ν34 ¼ 0:4793∠78° ν44 ¼ 0:0038∠0°
TABLE 2
Eigenvalues and eigenvectors of lateral-directional motion.
Lateral-directional λ1 ¼ 1:33 þ 1:75i λ2 ¼ 1:33 1:75i λ3 ¼ 1:81 λ4 ¼ 0:17
Δv ν11 ¼ 0:0363∠ 131° ν21 ¼ 0:0363∠131° ν31 ¼ 0:1313∠0° ν41 ¼ 0:7647∠0°
Δp ν12 ¼ 1∠0° ν22 ¼ 1∠0° ν32 ¼ 0:9125∠0° ν42 ¼ 0:4∠0°
Δr ν13 ¼ 0:5026∠150° ν23 ¼ 0:5026∠ 150° ν33 ¼ 1∠0° ν43 ¼ 0:0235∠180°
Δϕ ν14 ¼ 0:1969∠ 127° ν24 ¼ 0:1969∠127° ν34 ¼ 0:2125∠180° ν44 ¼ 1∠180° indicates the following characteristic changes the hydrodynamic coeffi- analysis are based on the Slocum modes: cients, which affects the eigenmodes model used in earlier studies (Graver, ■ a slowly converging, coupled roll of the glider dynamics. There are sev- 2005; Bhatta, 2006). Stability of and yaw rate mode, eral methods to obtain hydrodynamic steady motion is obviously affected ■ aslowlyconvergingmodeinvolv- coefficients, including analytical, by vehicle speed; in order to make ing roll angle and side velocity, and experimental, and computational ap- reasonable comparisons between dif- ■ an underdamped mode in which the proaches (Geisbert, 2007). For anal- ferent flight conditions, we fixtheflight roll rate and yaw rate are strongly ysis of general trends, as described speed at V = 0.77 m/s, as in previous coupled. here, a semiempirical approach is suf- studies. ficient (Nelson, 1998). Figure 12 shows root locus plots for 5.2. Glider Stability Varied Again, the physical and hydro- longitudinal modes in wings-level With Geometry dynamic characteristics used in this flight at maximum speed (left) and at Here, we investigate the effect of FIGURE 12 specific geometric parameters on the eigenvalue distribution. We consider Root locus plots for longitudinal modes with the parameter lw. (Root locus branches begin at red two specific flight conditions: maxi- circles and end at blue squares.) (a) Maximum speed. (b) Minimum glide angle. mum horizontal speed and minimum glideangle.Wepresentrootlocus plots for the longitudinal modes, in terms of the longitudinal wing loca- l tion w, and for the lateral-directional modes, in terms of vertical stabilizer l S location v and area v, as well the dihe- C dral parameter lβ (which accounts for the effect of wing sweep, dihedral angle, and vertical placement). The l l S variation of parameters w, v,and v
94 Marine Technology Society Journal minimum glide angle (right) in terms FIGURE 13 l of the parameter w. In these plots, l l Root loci for lateral-directional modes with parameter v. (Root locus branches begin at red circles w varies from zero (in which case and end at blue squares.) (a) Maximum speed. (b) Minimum glide angle. the wing is aligned with the center of buoyancy) to 0.2 l. Note that the farther aft the wing is located, the more stable the glider longitudinal dynamics become, due in part to the increased pitch damping. Figure 13 shows root locus plots for the lateral-directional modes in wings- level flight at maximum speed (left) and at minimum glide angle (right) l in terms of the parameter v.Inthese l l l plots, v varies from 0.5 to , that is, from the stern of the hull to a half- vehicle length aft of the stern. The FIGURE 14 farther aft the vertical stabilizer is located, the more stable the glider Root loci for lateral-directional modes with parameter Sv. (Root locus branches begin at red circles lateral-directional dynamics become, and end at blue squares.) (a) Maximum speed. (b) Minimum glide angle. due to increasing yaw stiffness and damping. Figure 14 shows root locus plots for the lateral-directional modes in wings-level flight at maximum speed and at minimum glide angle S in terms of the parameter v,which varies from half the hull frontal area to 1.2 times the hull frontal area. Note that a larger vertical stabilizer area yields more stable lateral-directional modes, by increasing yaw stiffness anddamping.Figure15showsroot locus plots for the lateral-directional fl modes in wings-level ight at maximum FIGURE 15 speed and at minimum glide angle in C C terms of the parameter lβ , which var- Root loci for lateral-directional modes with parameter l β . (Root locus branches begin at red ies from “more negative” (−0.8) to “less circles and end at blue squares.) (a) Maximum speed. (b) Minimum glide angle. negative” (−0.2). Note that larger neg- ative values of this parameter (corre- sponding to wings with larger sweep angle, larger dihedral angle, or higher vertical placement) yield more stable lateral-directional dynamics. Of course, greater stability implies that greater control authority is required to effect a maneuver, such as a turn. Tradeoffs between control authority and stabil- ity are fundamental in vehicle design
May/June 2013 Volume 47 Number 3 95 and they suggest the need for guide- found that a smaller roll angle is required to effect a steady turn at a given rate lines. For manned vehicles, such guide- when the vertical tail volume and/or the dihedral effect is smaller. We also pro- lines are obtained based on crew and vided simple methods to estimate range and endurance; a more sophisticated passenger comfort, but for unmanned analysis would incorporate details of the buoyancy lung mechanization as well vehicles they must be derived from as the variation of water density and hull compressibility.Turning to stability, other considerations such as payload we used root locus analysis to examine the variation in longitudinal and lateral- motion. directional eigenvalues with changes in wing location, wing shape, and vertical sta- bilizer size and location. We found that the farther aft the wing is located, the more stable the glider longitudinal dynamics become, due in part to the increased pitch 6. Conclusion damping. The farther aft the vertical stabilizer is located and/or the larger the vertical Considering a conventional under- stabilizer area is, the more stable the glider lateral-directional dynamics become, due water glider configuration comprising to the increasing yaw stiffness and damping. Also, a larger dihedral effect yields a cylindrical hull, a simple trapezoidal more stable lateral-directional modes; dihedral effect can be increased by increas- wing and a vertical stabilizer, we have ing sweep or dihedral angle and by placing the wings higher on the hull. Increased provided analysis to describe the effect stability may provide better response to disturbances, but may also limit control of a few important geometric param- authority, a tradeoff that must be considered in vehicle design. eters on steady wings-level flight and steady turning flight. Starting from an 8-degree-of-freedom model that Acknowledgments fi incorporates a cylindrically actuated The authors gratefully acknowledge the sponsorship of the Of ce of Naval Research fi moving point mass, we considered under Grant #N00014-08-1-0012. The rst author would like to thank the China fi two important wings-level gliding con- Scholarship Council (CSC) for nancial support during her visit to Virginia Tech. ditions: minimum glide angle and maximum horizontal speed. We also Corresponding Author: developed approximate analytical ex- Shuangshuang Fan pressions for steady turning motion in The State Key Lab of Fluid Power Transmission and Control, terms of the cylindrical actuation Zhejiang University, Hangzhou, China scheme and investigated the relationship Email: [email protected] between glider geometric parameters and the vehicle’s performance and sta- bility characteristics. The geometric Appendix A. Body/Particle/Fluid System Energy parameters characterized the slender- To derive the equations of motion for an underwater glider with a moving mass nessofthehull,thepositionand particle, one first determines the kinetic energy of the body/particle/fluid system shape of the wing, and the size and po- in order to compute the momenta. The particle kinetic energy is sition of the vertical stabilizer. We 1 T 1 T found, for example, that for a glider Tp ¼ mpνp νp ¼ η Mp rp η 2 2 of given mass and buoyant lung capac- ity, higher speeds are attainable using where longer hull lengths, smaller wing 0 1 m I m ^ m m ^ spans, larger hull fineness ratios, and 0 10 1T p prp pe1 prpe1 I I B C higher wing aspect ratios. To maxi- B CB C B m ^ m ^ ^ m ^ m ^ ^ C B r^p CB r^p C B prp prprp prpe1 prprpe1 C M ¼ m ¼ B C mize the lift-drag ratio at a given min- p rp pB T CB T C B C @ e A@ e A Bm T m T^ m 0 C 1 1 pe1 pe1 rp p imum glide angle speed, on the other T T @ A e r^p e r^p hand, one should decrease the hull 1 1 m T^ m T^ ^ 0 m T^ ^ pe1 rp pe1 rprp pe1 rprpe1 length and increase the wingspan ratio. Adapting a regular perturba- tion approach to develop analytical ex- Here and elsewhere in the text, 0 represents a matrix of zeros whose dimensions pressions for steady turning flight, we are clear from context.
96 Marine Technology Society Journal T The kinetic energy b of the mass References Lanchester, F.W. 1908. Aerodonetics. particle representing the buoyancy Bhatta, P. 2006. Nonlinear stability and London: A. Constable and Co. 468 pp. fi control of gliding vehicles. Ph.D. thesis, control system is de ned similarly. Mahmoudian, N., Geisbert, J., & Woolsey, Princeton University. 206 pp. The generalized mass matrix is C.A. 2010. Approximate analytical turning 0 1 Bhatta, P., & Leonard, N.E. 2008. Nonlinear conditions for underwater gliders and impli- mbI mbr^b 0 gliding stability and control for vehicles cations for path planning. IEEE J Oceanic B C B C with hydrodynamic forcing. Automatica. Eng. 35(1):131-43. http://dx.doi.org/10.1109/ Mb ¼ @mbr^b mbr^br^b 0 A 44(5):1240-50. http://dx.doi.org/10.1016/ JOE.2009.2039655. 000 j.automatica.2007.10.006. Mahmoudian, N., & Woolsey, C.A. 2013. Curtin, T.B., Bellingham, J.G., Catipovic, J., An efficient motion control system for under- Where rb denotes the location of & Webb, D. 1993. Autonomous oceano- water gliders. Nonlinear Engineering: Modeling the mass particle in the body frame. graphic sampling networks. Oceanography. and Application, 2013. (To appear.) Since we have assumed the buoyancy 6(3):86-94. http://dx.doi.org/10.5670/ Mises, R.V. 1959. Theory of Flight. control system is at the body frame oceanog.1993.03. T New York: Dover. 672 pp. origin, however, rb = [0, 0, 0] . Eriksen, C.C., Osse, T.J., Light, R.D., Wen, T., The kinetic energy of the rigid Nelson, R.C. 1998. Flight Stability and Auto- Lehman, T.W., Sabin, P.L., … Chiodi, A.M. body portion of the glider is also qua- matic Control. New York: McGraw-Hill 2001. Seaglider: A long-range autonomous dratic in η, with the generalized mass Higher Education. 441 pp. underwater vehicle for oceanographic research. matrix IEEE J Oceanic Eng. 26(4):424-36. http:// Osse, T.J., & Eriksen, C.C. 2007. The 0 1 dx.doi.org/10.1109/48.972073. deepglider: A full ocean depth glider for mrbI mrbr^rb 0 B C oceanographic research. In: Proc MTS/IEEE B C Etkin, B., & Reid, L.D. 1996. Dynamics of Mrb ¼ m ^ 0 OCEANS. pp. 1-12. Vancouver, BC: IEEE. @ rbrrb J rb A Flight: Stability and Control. New York: 000 John Wiley and Sons. 400 pp. Pamadi, B.N. 2004. Performance, Stability, Dynamics and Control of Airplanes. Reston, Galea, A.M. 1999. Optimal path planning VA: AIAA. 780 pp. http://dx.doi.org/10.2514/ where Jrb is the matrix of rigid body and high level control of an autonomous 4.862274. moments of inertia. gliding underwater vehicle. Master thesis, Finally, define the generalized added Massachusetts Institute of Technology. Rudnick, D.L., Davis, R.E., Eriksen, C.C., mass matrix 67 pp. Fratantoni, D.M., & Perry, M.J. 2004. Underwater glider for ocean research. 0 1 Graver, J., Liu, J., Woolsey, C.A., & Leonard, T Mar Technol Soc J. 38(1):48-59. M f Cf 0 N.E. 1998. Design and analysis of an under- M ¼ @ A f Cf J f 0 water vehicle for controlled gliding. In: Proc Sherman, J., Davis, R.E., Owens, W.B., & 000 CISS. pp. 801-6. Princeton, NJ: IEEE. Valdes, J. 2001. The autonomous under- water glider “Spray”. IEEE J Oceanic Eng. Graver, J.G. 2005. Underwater gliders: 26(4):437-46. http://dx.doi.org/10.1109/ where the component submatrices Jf, Dynamics, control and design. Ph.D. thesis, M 48.972076. f,andCf represent added inertia, Princeton University. 273 pp. added mass, and hydrodynamic cou- Stengel, R.F. 2004. Flight Dynamics. Princeton, Geisbert, J.S. 2007. Hydrodynamic modeling pling between the translational and ro- NJ: Princeton University Press. 845 pp. for autonomous underwater vehicle using tational motion of the rigid body. computational and semi-empirical methods. Teledyne Webb Research. 2013. Electric The total kinetic energy of the rigid fl Master thesis, Virginia Tech. 87 pp. glider. http://www.webbresearch.com/ body/particle/ uid system is electricglider.aspx, April 2013. Hoerner, S.F. 1965. Fluid Dynamic Drag. 1 T Midland Park, NJ: Author. 452 pp. T ¼ Tp þ Tb þ Trb þ Tf ¼ η M rp η USAF Stability and Control Datcom. 1978. 2 Flight Control Division, Air Force Flight Jenkins, S.A., Humphreys, D.E., Sherman, J., Dynamics Laboratory. Fairborn, OH: Osse, J., Jones, C., Leonard, N.E., …, Wasyl, J. Wright Patterson Air Force Base. where 2003. Underwater glider system study. Technical Report 53, Office of Naval Research (ONR). Webb, D.C., Simonetti, P.J., & Jones, C.P. M ¼ M þ M þ M þ M : rp p rp b rb f 240 pp. 2001. SLOCUM: An underwater glider
May/June 2013 Volume 47 Number 3 97 propelled by environmental energy. IEEE J Oceanic Eng. 26(4):447-52. http://dx.doi.org/ 10.1109/48.972077.
Wolek, A., Burns, J., Woolsey, C.A., Techy, L., Quenzer, J., & Morgansen, K. 2012. A maneuverable, pneumatic underwater glider. In: Proc MTS/IEEE OCEANS. October 14–19, 2012. Virginia Beach, VA: IEEE.
98 Marine Technology Society Journal PAPER Analysis of Underwater Acoustic Communication Channels
AUTHORS ABSTRACT Sadia Ahmed The underwater acoustic communication (UAC) channel presents many difficul- Huseyin Arslan ties such as high frequency, space, and time selectivity, frequency-dependent Department of Electrical noise, and significant range and band limitation on transmission. Traditional UAC Engineering, University of channel models that model such channels primarily include environmental models South Florida based on experimental data; models that are developed using mathematical equa- tions such as wave equations, modal methods, and parabolic equations; and using statistical distributions. These methods/models are often limited in their coverage Introduction and accurate representations of every possible UAC channel environment. It is also he underwater acoustic commu- physically impractical and cost ineffective to try to measure/estimate each channel nication (UAC) channel is vast and to determine its model. In this paper, the authors will present the analysis of UAC T channels according to the UAC channel environments classified and presented in varying in nature. The existing UAC channel models may not be sufficient a prior work by the authors, in which cognitive intelligence is used in the selection to represent every single UAC chan- of the appropriate channel representations according to each sensed environment. nel scenario. Moreover, the choice of To the best knowledge of the authors, this type of analysis and representation of models from the existing ones may UAC channels with respect to each UAC environment has not been addressed in the fi notbeaccuratetorepresentthetrue literature to date and therefore presents a signi cant contribution. channel environment. Thus, the vary- Keywords: channel representation, deep channel, shallow channel, underwater ing nature of the UAC channel re- channel environment quires representing of such channel according to its channel environment, whichinturnisspecified by sets of The contributions of this paper are a brief literature review of UAC channel parameters. If the channel as follows: channel models. Mapping of UAC parameters and hence the channel en- ■ This paper presents an analysis of Channel Parameters to UAC Channel vironment is accurately determined, UAC channel impulse response Environments discusses the mapping the environment can be mapped onto according to each broadly catego- of UAC channel environment param- the appropriate UAC channel repre- rized UAC channel environment eters onto UAC channel environments. sentation (Ahmed & Arslan, 2009a, (Figure 1). UAC Channel Representation Accord- 2009b). The same channel represen- ■ Fading characteristics of the re- ing to Environment presents the anal- tations can be reapplied in same or ceived signal and signal-to-noise ysis of channel impulse response and similar environments. The parameter ratio (SNR) of UAC channel in fading characteristics of UAC channels values can be adaptively measured/ each channel environment and according to channel environments. estimated or derived according to the the relationship between envi- SNR Analysis provides the SNR analy- UAC environment. Therefore, the rela- ronment parameters and differ- sis of the channel representations. Ben- tionship between UAC channel repre- ent types of fading are analyzed efits of Channel Classification and sentations and the UAC environments and discussed. Selection of Channels briefly presents allows wider representation and cover- ■ The channel representations are the benefits of channel selection and age of the varying UAC channels. generated using the AcTUP soft- the channel selection methods. Simula- A high level classification of the UAC ware module. tion Results presents the simulation re- channel environments according to The rest of the paper is organized sults, and Conclusion addresses the literature is presented in Figure 1. as follows. Related Works presents concluding remarks.
May/June 2013 Volume 47 Number 3 99 FIGURE 1 loss characteristics and incorporates features such as surface wave model, Identification and high-level classification of UAC channel environments. internal wave model, tidal currents model, two-layer bottom interactions, and ambient noise. Second, 3-D ray tracing is used to develop the propaga- tion model that includes effects such as range dependent bathymetry, branch- ing at the water/sediment interface, propagation through the sediment layer, range-dependent sound speed, caustics, reflection from the moving sea surface, and motion of transmitter/ receiver platforms. In the current paper, the effect of environment parameters and the prop- agation characteristics are incorpo- rated in the deterministic and stochastic components of the arrived paths. In Geng and Zielinski (1995), the random fluctuation of dominant eigen paths between transmitter and receiver is represented by the presence of smaller sub-eigen paths. The com- bination of eigen and sub-eigen paths is represented by Rician fading. In Bjerrum-Niese and Lutzen (2000), signal-to-multipath ratio and signal fading statistics is presented. Turbu- lence of water causes change in signal Related Works mitter and receiver motion. In this phase and amplitude. Ray tracing is The UAC channels are presented model, the eigen rays corresponding used to determine the deterministic fl using stochastic models in some litera- to direct/re ected multipaths are de- component and phase and amplitude ture. In Galvin and Coats (1996), the termined using ray tracing while the variation is placed on top of the deter- random diffusive multipaths are mod- ministic components. amplitude and phase fluctuation of eled using Rayleigh fading. In the current paper, the determin- received signal is presented first by lin- In the current paper, the random istic eigen components are first derived ear and then nonlinear transformations fluctuation due to diffusive paths are using Ray tracing and then the random of Gaussian variables. In Morozov represented as Rayleigh or Rician vari- fluctuation causing sub-eigen compo- (1995), the estimation of slow phase ables according to the environment. nents are placed on top of the determin- fl uctuations of channel impulse re- In Appleby and Davies (1998), istic components. The combined effect ’ sponse is described as Markov s process, time and frequency dispersion of of eigen and sub-eigen is represented as and the accumulation of impulse chan- UAC channel is represented by a Gaussian, Rayleigh, or Rician variables. nel responses is decided by the Viterbi model, which encompasses two sepa- In Walree et al. (2008) and algorithm. In Byun et al. (2007), a chan- rate modeling stages. First, the envi- Socheleau et al. (2011), data are mea- nel model is proposed to present the ronment model is developed using sured and the measured data are inter- time-varying UAC channel, where the the environmental data such as wind polated to determine channel impulse time variation is produced by trans- speed, sound speed profile, bottom response (CIR). Both uncorrelated and
100 Marine Technology Society Journal correlated taps are considered. Pseudo- ■ Line-of-sight (LOS) path is con- Geng & Zielinski, 1995) accompanied random binary signal is used as probe sidered to be present in each UAC by less dominant paths or sub-eigen signal in the measurements. environment. paths, for example, originating from The rest of this section is organized as various scatters. follows. Channel Impulse Response Mapping of UAC Channel of UAC Channels presents the CIR Shallow Channel Representation Parameters to UAC and Fading Characteristics, Probability According to Environment Channel Environments Distribution, Relationship Between A generic shallow water channel is The cognitive intelligence (CI) al- Fading and Channel Parameters for illustrated in Figure 2. The shallow gorithms to map UAC channel param- Wide Sense Stationary (WSS) Un- water UAC channel multipaths can eters to environments and to map correlated Tap Channel presents the be grouped according to their origina- UAC environments to channel models fading characteristics of different UAC tion. In a shallow UAC channel envi- have been presented in Ahmed and channels according to each UAC ronment, there may be five groups of Arslan (2009a, 2009b), respectively. environment. Frequency Dependent eigen and sub-eigen paths. The first All possible UAC channel environ- and Independent Noise briefly touches group of paths may result from surface ments may be determined from the on the noise components and Fading only reflection and scatter, while the sensed channel environment parame- Characteristics, Distribution, Rela- third group may result from bottom ters. The channel representations, once tionship Between Fading and Chan- only reflection, bottom refraction, mapped from the environments, will nel Parameters for Quasi-stationary and scatter. The second group may in- be more accurate since they are derived Channels on quasistationarity of UAC clude paths that reflect on both surface from the actual channel environments. channels. and bottom but the first reflection is on the surface. The fourth group may fl Channel Impulse Response also include paths re ecting on both UAC Channel fi fl of UAC Channels surface and bottom but the rst re ec- Representation According tion is on the bottom. There may be Let the transmitted signal be denoted to Environment scatters associated with these paths by an impulse, δ(t), where δ represents a In the proposed channel analysis, as well. Depending on the transmis- Dirac delta function. The UAC channel the following assumptions are made. sion range and depth, sound refrac- will produce multipaths that may vary Channel Assumptions tion through water layers may result in in time. In a time invariant channel, ■ The channel equations are derived in the time domain. The transmis- the channel impulseP response can be ex- h τ L 1 α δ τ −τ FIGURE 2 sion frequency and bandwidth are pressed as ( REF)= l¼0 l ( REF l). The variables αl and τl denote the considered as parameters defining Underwater acoustic shallow water channel. fi the UAC environment (Ahmed & attenuation coef cient and the time l Arslan, 2009a). delay of the th path respectively. The variable L denotes the total number of ■ Power in terms of path loss in dB τ is considered for each path in the multipaths, REF is a time reference. power delay profile. In a time variant channel, this equa- fi ■ Time variation of channel is applied tion can be modi ed as below, on top of the power delay profile. XL 1 hðÞ¼τREF ; t αl ðÞt δτðÞREF τl ðÞt : ■ The individual scatters are assumed l¼0 to be independent and identically ð1Þ distributed (i.i.d.) Gaussian random variables in the case of uncorrelated In an UAC channel, group of multi- taps. paths may consist of dominant paths, ■ Each dominant and its correspond- for examples, originating from reflec- ing sub-eigen paths arrive at the tions on the boundaries, also known receiver at the same time. as eigen paths (Gutierrez et al., 2005;
May/June 2013 Volume 47 Number 3 101 another group of eigen and sub-eigen paths. This fifth group may also include FIGURE 3 paths resulting from reflection, refraction, and scatter on marine life and other Single path originated from each group in UAC objects in the water medium. In addition, there may be a direct LOS that may shallow channel. Solid line represents eigen paths, depend on transmission range and depth. Equation (1) can be expanded to repre- and dashed line represents sub-eigen paths. sent channel impulse response for all these five groups of paths as below. XII XI hðtÞ¼α0ðtÞδðtÞþ αiðtÞδðt τiðtÞÞ þ αiiðtÞδðt τiiðtÞÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}i¼1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}ii¼IIþ1 GROUP 1 GROUP2 XJJ À Á XJ À Á þ αjðtÞδ t τjðtÞ þ αjjðtÞδ t τjjðtÞ j¼Iþ jj¼JJþ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 GROUP3 GROUP4 XL 1 Á þ αkðtÞδðt τkðtÞ : ð2Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}k¼Jþ1 GROUP 5 source and destination denoted by D, Table 1 presents examples of dominant paths in these groups. source and destination depth from sur- z z Each group of (2) can be expanded into many eigen paths and their corre- face denoted by s and r respectively, sponding sub-eigen paths as in (3). Each eigen and its sub-eigen paths arrive at the and water column height between sur- H same time at each delay. face and bottom denoted by . There " # are four such image sources and are M À Á X1 1 À Á GROUP ¼ α ðtÞδ t τ þ α ðtÞδ t τ given by Lurton (1996). 1 1 1 1m1 1 m1¼2 " # z v ¼ ðv ÞH þ zs zr M 1 2 1 À Á X2 1 À Á z v ¼ 2ðv 1ÞH þ zs þ zr þ α ðtÞδ t τ þ α m ðtÞδ t τ ::: 2 ð Þ 2 2 2 2 2 z ¼ vH z z 4 m ¼ ð3Þ 3v 2 s r " 2 2 # z4v ¼ 2vH zs þ zr : À Á MXII 1 À Á ::: þ α ðtÞδ t τ þ α ðtÞδ t τ : |fflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflffl}II II IImII II mII ¼2 Eigenpath |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl} Then the time delay of each multipath Sub eigenpaths at the destination can be expressed as
Rangewv Figure 3 illustrates one single dominant path originating in each group along with τwv ¼ ; ð5Þ less dominant paths due to scatters. c In an ideal scenario, with a smooth surface and a smooth bottom boundary, where w = 1, 2, 3, 4 denotes the image the channel generated multipaths can be described as arriving from image sources source types and c denotes the sound (Lurton, 1996). Under this scenario, the range traversed by each path from source velocity. The values of v can be v =1, to destination denoted by Rangewv can be expressed in terms of the distance between 2, 3…. If only path loss is considered TABLE 1 and the sound velocity is considered constant (the value is provided in sim- fi Shallow water channel: The ve groups and their respective paths. ulation), each multipath from indi- Group Paths in the Group vidual image source will go through path loss given by Lurton (1996), GROUP1
GROUP2 TLwv ¼ 20logRangewv þ βRangewv; ð6Þ GROUP3 where β is the water absorption coeffi- GROUP4 cient with units of dB/Km.Inthisideal GROUP5 scenario, in the absence of scatters, each
102 Marine Technology Society Journal path arriving from each image source will only consist of a dominant path. The amplitude of each path derived from (6) can be expressed as
TLwv: Awv ¼ 10 10 ð7Þ
In case of a smooth surface and a smooth bottom and in the absence of sub-eigen paths, there will only be dominant paths; the CIR will consist of one LOS, one surface reflected path (GROUP1), one bottom reflected path (GROUP3), multiple paths in GROUP2, and multiple reflected paths in GROUP4. Therefore, in the absence of sub-eigen paths, (2) becomes À Á XI À Á hðtÞ¼α ðtÞδðtÞþ α ðtÞδ t τ þ α ðtÞδ t τ ðtÞ 0 |fflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflffl}1 1 ii ii ii¼II þ1 GROUP1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl} GROUP2 À Á XJ À Á þ α ðtÞδ t τ ðtÞ þ α ðtÞδ t τ ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}JJ JJ jj jj jj¼JJ þ1 GROUP3 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl} GROUP4
LX 1 À Á þ αkðtÞδ t τkðtÞ ð8Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}k¼Jþ1 GROUP5
The above ideal scenarios generate deterministic path components. Now, let the smooth surface and smooth bottom be replaced by surface waves and a rough bottom, respectively. Let the following conditions be assumed: (a) the transmitter and the receiver are stationary; (b) the water column height (vertical distance between surface and bottom) remain the same for both transmitter and receiver; (c) the acoustic wave length is much larger than the wave surface and bottom reflector elements; (d) the dominant paths arrive at the receiver; and (e) the delays of dominant paths are calculated using image sources, although the surface movement due to surface waves and the presence of rough bottom may vary these dominant path delays. The scatters induced by surface waves and rough bottom may produce sub-eigen paths that can be represented as stochastic path components along with each dominant path. Then (8) becomes
M À Á X1 1 À Á hðtÞ¼α ðtÞδðtÞþ α ðtÞδ t τ þ α ðtÞδ t τ 0 1 1 1m1 1 m ¼ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 2 GROUP1
XI À Á MMXii 1 À Á þ α ðtÞδ t τ ðtÞ þ α ðtÞδ t τ ðtÞ ii ii iimmii ii ii|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}¼IIþ1 mmii¼2 GROUP2 À Á PXJJ 1 À Á þ α ðtÞδ t τ þ α ðtÞδ t τ JJ JJ JJpJJ 3 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}pJJ ¼2 GROUP3
XJ À Á PPXjj 1 Á þ α ðtÞδ t τ ðtÞ þ α ðtÞδðt τ ðtÞ jj jj jjppjj jj jj¼JJþ pp ¼ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 jj 2 GROUP4
XL 1 À Á QXk 1 À Á þ α ðtÞδ t τ ðtÞ þ α ðtÞδ t τ : ð Þ k k kqk k 9 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}k¼Jþ1 qk ¼2 GROUP5
May/June 2013 Volume 47 Number 3 103 Let the combination of each dominant and its corresponding sub-eigen paths be denoted as R′index(t). Using (9), h(t) can be expressed as the sum of variables as below,
hðtÞ¼h ðtÞ¼α ðtÞδðtÞþ R ðtÞ SBET 0 |ffl{zffl}1 GROUP1 þ R ðtÞþR ðtÞþ::: þ R ðtÞ þ R ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}IIþ1 IIþ2 I |fflffl{zfflffl}JJ GROUP2 GROUP3 þ R ðtÞþR ðtÞþ::: þ R ðtÞ þ R ðtÞþR ðtÞþ:::R ðtÞ; ð Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}JJþ1 JJþ2 J |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 10 GROUP4 GROUP5
GROUP fl GROUP fl where 1 denotes the surface only re ected/scattered paths, 3 denotes bottom only re ected/scattered paths, GROUP fl and 5 denotes paths corresponding to refraction in the medium and refraction/re ection/scatter on other objects. GROUP fl GROUP The 2 represents the surface/bottom re ected/scattered paths, while 4 represents the bottom/surface reflected/scattered paths. It is to be noted that arrival time of groups of paths and paths within the groups may vary. According to Figure 1, the shallow channel can be classified into three broad categories. They are close to surface, close to bottom, and in between channels. The surface and bottom roughness dictates further classification of shallow channel environment. The channel representations for these environments are given below. A channel that represents a shallow channel communication environment in between surface and bottom can be expressed h t by (10), where SBET ( ) denotes the channel impulse response. Depending on how close to the surface and/or to the bottom h h the source and destination are, both CIR, SS and SB , for close to surface and close to bottom environment respectively, may have paths in GROUP1 through GROUP4. 1) Shallow Channel Close to Rough Surface: Similar to a channel somewhere in between surface and bottom, a close to rough surface shallow channel can be expressed as (10). If however the bottom is far away from the surface in a close to rough surface communication environment, strictly ideally, the bottom reflected dominant paths may disappear due to higher loss and/or longer delay in arriving. Under such scenario, GROUP3 will be empty, and in GROUP2 and GROUP4 only surface scattered sub-eigen paths will dominate. Let the combination of scattered sub-eigen paths generated only from the surface corresponding to each negligible surface/bottom reflected dominant paths be denoted by the variables R′index. In that case, h t (10) will reduce to SS ( ) as below,
h ðtÞ¼α ðtÞδðtÞþ R ðtÞ þ R′ ðtÞþR′ ðtÞþ::: þ R′ðtÞ SS 0 |ffl{zffl}1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}IIþ1 IIþ2 I GROUP1 GROUP2
þ R′ ðtÞþR′ ðtÞþ::: þ R′ðtÞ þ RJþ ðtÞþRJþ ðtÞþ:::RL ðtÞ : ð11Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}JJþ1 JJþ2 J |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 2 1 GROUP4 GROUP5
h t h t The CIR in a close to a rough surface for long, short, and medium range transmission can be expressed as SRS=L ( ), SRS=S ( ), h t and SRS=M ( ), respectively. The expressions for these are derived from (11). In a long range close to rough surface transmission, the sub-eigen paths due to scatter are negligible and hence may result in GROUP2 and GROUP4 of (11) to be empty. Surface reflected dominant paths may dominate over the surface scattered R″ t fl sub-eigen paths. Let 1( ) denote the combination of surface re ected dominant path and negligible sub-eigen scatters. There may be horizontal variation of sound speed resulting in scatter and/or dominant paths due to refraction. Even though some reflection and scatters may occur due to objects in the medium, in a long range these may/may not be negligible. Hence GROUP5 may not be empty. Using (11), the CIR for transmission can be written as
h ðtÞ¼α ðtÞδðtÞþ R″ðtÞ þ R ðtÞþR ðtÞþ:::R ðtÞ : ð Þ SRS=L 0 |ffl{zffl}1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 12 GROUP1 GROUP5
In a short range close to rough surface transmission, surface scattered sub-eigen paths will be dominating. Therefore, GROUP2 and GROUP4 will not be empty. Due to short range, there may not be horizontal sound velocity variation
104 Marine Technology Society Journal but the presence of other objects in the water may result in reflection and scatters. If the range is short, the reflection/scatter fi h t on objects in the medium may be signi cant. Therefore, GROUP5 may not be empty. The resulting CIR, SRS=S ( ) will be as R t same as (11) with 1( ) having more dominant sub-eigen paths. In a medium range transmission, there may be dominant paths due to reflection and sub-eigen paths due to scatter. If the fl fi h t range is medium, the re ection/scatter on objects in the medium may be signi cant. The CIR of such a channel, SRS=M ( ) will be as same as (11). 2) Shallow Channel Close to Smooth Surface: In case of smooth surface, there will be no sub-eigen paths due to scatters on surface or bottom. Hence when the bottom is far away from the surface, ideally, GROUP2 and GROUP4 will be empty. For medium range transmission, (11) can be expressed as,
h ðtÞ¼α ðtÞδðtÞþR′″ðtÞ þ R ðtÞþR ðtÞþ:::R ðtÞ; ð Þ SSS=M 0 |fflffl{zfflffl}1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 13 GROUP1 GROUP5 R′″ fl where 1 denotes surface only re ected dominant path without any sub-eigen paths. Equation (13) also represents short range and long range close to smooth surface channels. 3) Shallow Channel Close to Rough Bottom: Similar to channels close to the surface, a close to rough bottom channel can be expressed as (10). If the surface is far away from the bottom, ideally, the surface reflected dominant paths will disappear h t R′ t due to higher loss and/or due to delay in arriving and (10) will reduce to SB ( ) as shown in (14). Variable Bindex( ) denotes the combination of sub-eigen scatters generated only from the bottom corresponding to each negligible surface/bottom reflected dominant path.
h ðtÞ¼α ðtÞδðtÞþR′ ðtÞþR′ ðtÞþ::: þ R′ ðtÞ SB 0 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}BIIþ1 BIIþ2 BI GROUP2
RJJ ðtÞ þ R′ ðtÞþR′ ðtÞþ::: þ R′ ðtÞ |fflffl{zfflffl} |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}BJJ þ1 BJJþ2 BJ GROUP3 GROUP4 þ R ðtÞþR ðtÞþ:::R ðtÞ : ð Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 14 GROUP5 h h The CIR in a close to a rough bottom for long-, short-, and medium-range transmission can be expressed as SRB=L , SRB=S , h fl and SRB=M , respectively. In a close to rough bottom shallow channel, in addition to bottom re ection, different bottom com- position may produce refracted scatters in GROUP2, GROUP3, and GROUP4. In long-range transmissions, these scatters may not have significant contribution and so, GROUP2 and GROUP4 may be empty. Then (14) becomes
hS ðtÞ¼α ðtÞδðtÞþ R″ ðtÞ þ RJþ ðtÞþRJþ ðtÞþ:::RL ðtÞ; ð15Þ RB=L 0 |fflffl{zfflffl}JJ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 2 1 GROUP3 GROUP5
where RJJ″(t) denotes combination of bottom reflected dominant path and negligible sub-eigen scatters. Different marine life and other objects on the ocean floor may produce scatters due to reflection and refraction. In long- range transmission, these scatters may not be significant but in short- and medium-range transmission, these scatters may be dominant. In short and medium range transmissions, strong bottom reflected/refracted scatters may also be dominant. h t R t Therefore, short range close to rough bottom transmission can be expressed as (14), denoted by SRB=S ( ), where JJ( ) will contain more dominant sub-eigen paths. A medium range close to rough bottom transmission can also be expressed as (14) h t and denoted by SRB=M ( ). 4) Shallow Channel Close to Smooth Bottom: In case of smooth bottom, there will be no sub-eigen paths due to scatters on the bottom. Hence for medium range transmission, (14) can be expressed as
hS ðtÞ¼α ðtÞδðtÞþ R′″ðtÞ þ RJþ ðtÞþRJþ ðtÞþ:::RL ðtÞ; ð16Þ SB=M 0 |fflffl{zfflffl}JJ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}1 2 1 GROUP3 GROUP5
May/June 2013 Volume 47 Number 3 105 ′″ where RJJ (t) denotes bottom only reflected dominant path without any sub-eigen steepest paths, GROUP2 denotes the paths. Equation (16) also represents short range and long range close to smooth axis paths, and GROUP3 denotes the h t h t fl bottom channels denoted by SSB=S ( ) and SSB=L ( ), respectively. bottom re ected paths. 2) Other Deep Channels: Deep Channel Representation According to Environment Isothermal Deep Channel: The If only path loss is considered, in a deep channel, each multipath will go CIR in isothermal channels for long-, through path loss given by Lurton (1996) and will arrive at various delays. medium-, and short-range transmis- h t In a deep channel, when the sound velocity is not constant, the first group of sion can be expressed as DISO=L;M;S ( ). multipaths represents the steepest paths, the second group represents grazing Forlong-,medium-,andshort-range paths for isothermal channel or axis paths for SOFAR channel, and the third transmission, not close to surface or group represents bottom reflected multipaths (Lurton, 1996). These paths are bottom, the scatters may be insignif- presented below. icant resulting in mostly dominant eigen paths similar to (18). For chan- MD 1 XID À Á XiD À Á nels close to surface or bottom, the h ðtÞ¼ α ðtÞδ t τ þ α ðtÞδ t τ D iD iD iDmD iD iD presence of significant scatters may re- iD¼1 mD ¼2 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}iD sult in an equation similar to (17). The GROUP1 first group of paths denotes the steepest PD 1 XJD À Á XjD À Á paths, the second one denotes grazing þ α ðtÞδ t τ þ α ðtÞδ t τ jD jD jDpD jD jD p ¼ paths, and the third one denotes the jD¼IDþ1 Dj 2 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}D bottom reflected paths. GROUP2
L QD 1 XD 1 À Á XkD À Á Fading Characteristics, þ α ðtÞδ t τ þ α ðtÞδ t τ : ð Þ kD kD kDqD kD 17 kD Probability Distribution, kD¼JDþ1 qD ¼2 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}kD Relationship Between Fading GROUP3 and Channel Parameters for Wide Sense Stationary (WSS) Although (17) considers both eigen and sub-eigen components, the existence of a Uncorrelated Tap Channel fewer number of scatters in a deep channel may only cause dominant eigen com- In determining the fading char- ponents to exist. The deep channel can be broadly categorized into SOFAR and acteristics and probability distribution other types of deep channels. of various UAC channels, the follow- 1) SOFAR Channel: The CIR in a SOFAR channel for long-, medium-, and ing assumptions are made: short-range transmission can be derived from (17). For long-, medium-, and Assumptions: short-range transmission, not close to surface or bottom, the scatters may be ■ Channel paths are considered at fi insigni cant resulting in only dominant components as below, each sample time. ■ I Intheabsenceofanaturalpath XD À Á h ðtÞ¼ α ðtÞδ t τ DSOF=L;M;S iD iD at any sample, a path is gener- |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}iD¼1 ated by interpolating neighboring GROUP1 paths. XJD À Á ■ The symbol period is considered þ α ðtÞδ t τ jD jD large enough to encapsulate all the jD¼IDþ1 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl} significant arrived multipaths. GROUP2 After convolving with the channel the LXD 1 À Á þ α ðtÞδ t τ : ð Þ received signal, using (1), can be ex- kD kD 18 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}kD¼JDþ1 pressed as GROUP3 XL 1 À Á rðtÞ¼α0ðtÞsðtÞþ αl ðtÞs t τl ; However, for SOFAR channels close to surface or bottom, there may be some l¼1 þ n ðtÞþn ðtÞ; ð Þ significant scatters that would result in (17). In both cases, GROUP1 denotes the 1 2 19
106 Marine Technology Society Journal s t n t n t G RL RC where the variables ( ), 1( ) and 2( ) a variable, , ,or identifying an amplitude with either Gaussian, Rayleigh, or denote the transmitted signal, frequency- Rician distribution, respectively. independent and frequency-dependent These variables are an indication of the channel environment and are directly noise, respectively. related to the environment parameters. For example, the value of the range param- When each arrived path is i.i.d. eter (short/medium/long) and/or depth parameter (close to surface/close to bot- Gaussian, the following conditions tom, etc.) may determine the variable at each sample location to be G, RL,orRC. may occur. Case a) When the dominant If the channel delay spread is long and some paths arrive outside of the symbol path to less dominant multipath ratio, duration, those outside paths will also contain combination of dominant and sub- which is denoted by signal to multipath eigen paths resulting in an amplitude variation, the distribution of which can be ratio, SMR is less than 1, i.e., SMR ≪ 1 presented by a Gaussian, Rayleigh, or Rician variable according to the channel en- the amplitude of the envelop of paths vironment. Figure 4 illustrates the relationship between the paths, the symbol du- follows Rayleigh distribution (Geng & ration, and the sample time. The received signal representation in terms of Zielinski, 1995). Case b) When the Gaussian, Rayleigh, or Rician fading for the UAC channels described in the last eigen path component dominates, as subsection are given below. The SMR for each path can be expressed as in the case of direct LOS, SMR ≫ 1, and the amplitude of the envelop of jEigenpathj SMRPath ¼ P : ð20Þ the paths follows Gaussian distribution. j SubEigenPathj Case c) When the dominant path is comparable to the less dominant paths, Depending on the value of SMRPath of each path, the combination of eigen and such that the dominant path exists as sub-eigen components will follow Rayleigh, Gaussian, or Rician distribution. If one single large path compared to the the symbol duration encapsulate all paths, then less dominant paths, i.e., SMR ≂ 1 jLOSj the amplitude of the envelop of the SMR ¼ P : ð Þ Symbol j Other j 21 paths follows Rician distribution. Path The symbol is sampled at each ar- rived multipath. Each path at each sam- Depending on the value of SMRSymbol, the combination of all paths (each path a ple location is a combination of eigen and combination of eigen and sub-eigen components) within the symbol duration will sub-eigen paths. At each sample location, follow Rayleigh, Gaussian, or Rician distribution. these simultaneous paths can add con- Fading characteristics of the shallow channel will be addressed first below, fol- structively or destructively. The ampli- lowed by the fading characteristics of the deep channel. tude of the resultant path at each sample (i) Fading characteristics of shallow channel: location can be subjected to one of the 1) Shallow Channel Close to Rough Surface: The received signal in a close to a three conditions mentioned above result- rough surface for long-, short-, and medium-range transmission can be expressed as r t r t r t ing in Gaussian, Rayleigh or Rician fading SRS=L ( ), SRS=S ( ), and SRS=M ( ), respectively. Using (12), in long-range transmission, distribution. Let each sample represent h i r ðtÞ¼G þ RC″ðtÞ SRS=L 0 |fflfflffl{zfflfflffl}1 FIGURE 4 RicianðGROUP Þ h 1 i þ RC ðtÞþRC ðtÞþ:::RC ðtÞ Channel paths, symbol duration, and sample |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 time: The bold lines represent dominant eigen RicianðGROUP5Þ and dashed lines represent sub-eigen paths. n1ðtÞþn2ðtÞ; ð22Þ Each arrived path within symbol duration and outside of symbol duration may consist of one RC″ t fl dominant and/or one/multiple sub-eigen paths. where 1( ) represents the Rician envelop corresponding to surface re ected dom- inant path and sub-eigen paths. Each of RCJs represent a Rician envelop corre- sponding to scatter/dominant paths due to refraction from sound speed variation and/or reflection/refraction/scatter on objects in the medium. The surface reflected path will produce Rician fading if the scatters are not negligible otherwise it will produce Gaussian fading.
May/June 2013 Volume 47 Number 3 107 In a short-range transmission, using (11), the received signal can be expressed as h i r ðtÞ¼G þ RL ðtÞ SRS=S 0 |fflfflffl{zfflfflffl}1 RayleighðGROUP1Þ h i þ RL′ ðtÞþRL′ ðtÞþ::: þ ::: þ RL′ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}II þ1 IIþ2 I RayleighðGROUP2Þ h i þ RL′ ðtÞþRL′ ðtÞþ::: þ RL′ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}JJþ1 JJþ2 J RayleighðGROUP4Þ h i þ RL ðtÞþRL ðtÞþ:::RL ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 RayleighðGROUP5Þ
þ n1ðtÞþn2ðtÞ; ð23Þ RL t fl where 1( ) represents the Rayleigh envelop corresponding to surface re ected path and dominant scattered sub-eigen paths. The RL′II sandRL′JJ s represent Rayleigh envelop of combination of surface scattered sub-eigen paths corresponding to each negligible surface/bottom reflected (first reflection on surface for GROUP2 and first reflection on bottom for GROUP4) dom- inant path. Each of RLJs represent a Rayleigh envelop corresponding to scatter/dominant paths due to refraction from sound speed variation and/or reflection/refraction/scatter on objects in the medium. In a medium range, paths in GROUP5 will result in some Rician variables and some Rayleigh variables. Therefore, using (11), h i r ðtÞ¼G þ RC ðtÞ SRS=M 0 |fflfflffl{zfflfflffl}1 RicianðGROUP Þ h 1 i þ RL′ ðtÞþRL′ ðtÞþ::: þ RL′ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}II þ1 II þ2 I RayleighðGROUP Þ h 2 i þ RL′ ðtÞþRL′ ðtÞþ::: þ RL′ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}JJ þ1 JJ þ2 J h RayleighðGROUP4Þ þ RC ðtÞþRC ðtÞþ:::RC ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 JþJ′ RicianðGROUP Þ h 5 i þ RL þ ðtÞþRL þ ðtÞþ:::RL ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}J′ 1 J′ 2 L 1 RayleighðGROUP5Þ
þ n1ðtÞþn2ðtÞ; ð24Þ RC t fl where 1( ) represents the Rician envelop of dominant surface re ected path and sub-eigen scatters. 2) Shallow Channel Close to Smooth Surface: In case of smooth surface, the received signal in long, short, and medium r t r t r t range can be denoted as SSS=L ( ), SSS=S ( ), and SSS=M ( ), respectively. The equations for long, short, and medium range will be same and using (13) can be expressed as h i r ðtÞ¼G þ G′″ðtÞ SSS=L;M;S 0 |fflfflffl{zfflfflffl}1 GaussianðGROUP1Þ h i þ G ðtÞþG ðtÞþ:::G ðtÞ þ n ðtÞþn ðtÞ; ð Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 1 2 25 GaussianðGROUP5Þ where G′″denotes the Gaussian variable corresponding to surface only reflected dominant path without any sub-eigen paths. The variable GJs denote Gaussian variables representing dominant paths due to refraction from sound speed variation and/or reflection/refraction on objects in the medium.
108 Marine Technology Society Journal 3) Shallow Channel Close to Rough Bottom: The received signal in a close to a rough bottom for long-, short-, and r r r medium-range transmission can be expressed as SRB=L , SRB=S , and SRB=M , respectively. In a long-range transmission, the bottom reflected/refracted paths will produce Rician fading, if the scatters are not negligible otherwise it will produce Gaussian fading. Therefore, using (15), h i h i r ðtÞ¼G þ RC′″ðtÞ þ RC ðtÞþRC ðtÞþ:::RC ðtÞ þ n ðtÞþn ðtÞ; ð Þ SRB=L 0 |fflfflfflffl{zfflfflfflffl}JJ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 1 2 26 RicianðGROUP3Þ RicianðGROUP5Þ where RCJJ″ represents the Rician envelop corresponding to bottom reflected dominant path and negligible sub-eigen scatters. Using (14), h i h i r ðtÞ¼G þ RL′ ðtÞþRL′ ðtÞþ::: þ RL′ ðtÞ þ RL ðtÞ SRB=S 0 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}BII þ1 BII þ2 BI |fflfflffl{zfflfflffl}JJ RayleighðGROUP2Þ RayleighðGROUP3Þ h i þ RL′ ðtÞþRL′ ðtÞþ::: þ RL′ ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}BJJ þ1 BJJþ2 BJ RayleighðGROUP4Þ h i þ RL ðtÞþRL ðtÞþ:::RL ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 RayleighðGROUP5Þ
þ n1ðtÞþn2ðtÞ; ð27Þ where RLBII′ sandRLBJJ′ s represent Rayleigh envelops of combination of bottom scattered sub-eigen paths correspond- ing to each negligible surface/bottom reflected path (first reflection on surface for GROUP2 and first reflection on bottom for GROUP4). In a medium range, paths in GROUP5 will result in some Rician variables and some Rayleigh variables. Therefore, using (14) h i r ðtÞ¼G þ RL′ ðtÞþRL′ ðtÞþ::: þ RL′ ðtÞ SRB=M 0 |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}BIIþ1 BIIþ2 BI RayleighðGROUP2Þ h i þ RCJJ ðtÞ þ RL′ ðtÞþ::: þ RL′ ðtÞ |fflfflffl{zfflfflffl} |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}BJJþ1 BJ RicianðGROUP3Þ RayleighðGROUP4Þ h i þ RC ðtÞþRC ðtÞþ:::RC ðtÞ þ RL ðtÞþRL ðtÞþ:::RL ðtÞ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 JþJ′ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}J′þ1 J′þ2 L 1 RicianðGROUP5Þ RayleighðGROUP5Þ
þ n1ðtÞþn2ðtÞ; ð28Þ where RCJJ (t) represents the Rician variable corresponding to the bottom reflected dominant path and sub-eigen scatters. r r 4) Shallow Channel Close to Smooth Bottom: In case of smooth bottom, the equations can be expressed as SSB=L , SSB=S , r and SSB=M . Expressions for short, medium, and long range will be same and using (16) can be expressed as h i rS ðtÞ¼G þ G′″ðtÞ SB=S 0 |fflfflffl{zfflfflffl}JJ GaussianðGROUP3Þ h i þ G ðtÞþG ðtÞþ:::G ðtÞ þ n ðtÞþn ðtÞ; ð Þ |fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Jþ1 Jþ2 L 1 1 2 29 GaussianðGROUP5Þ where G′″JJ represents the Gaussian variable corresponding to bottom reflected dominant path.
May/June 2013 Volume 47 Number 3 109 5) Shallow Channel in Between FIGURE 5 will be affected. Frequency-dependent Surface and Bottom: The received noise is included under n (t). Shallow channel: (a) Long-range, high-depth, 2 signal in an environment between sur- and low-frequency Rician fading zone. (b) Short- face and bottom will be affected by range, low-depth, and high-frequency Rayleigh Fading Characteristics, both surface and the bottom. The type fading zone. Distribution, Relationship of channel for long, short, and medium Between Fading and range transmission can be expressed as Channel Parameters for r r r SBET =L , SBET =S , and SBET =M respectively. Quasi-stationary Channels r The equation for SBET =L can be expressed In UAC channel, wide sense sta- r r as a combination of SSS=L and SSB=L , tionary (WSS) assumption is not always when both surface and the bottom are true (Bjerrum-Niese & Lutzen, 2000; smooth. If either or both are rough, Socheleau et al., 2011; Walree et al., the equations can be modified to include 2008). When the transmitter and the r more scatters. Similarly, SBET =S will be receiver or their platforms are moving, r r a combination of SSS=S and SSB=S ,and the various taps can be correlated at r r SBET =M will be a combination of SSS=M different delays. There are different ap- r the deep channel is close to surface/ and SSB=M . Rough surface/bottom will proaches to address non-WSS chan- add scatters and equations will change bottom, the fading characteristics of nels. One method is to consider the accordingly. In a clear, unobstructed close to surface, close to bottom or in channel as quasi-WSS, i.e., the channel channel, the increase of transmission between channels may apply. is WSS within a certain time and band range and water column depth will of frequency. Another way of dealing produce dominant components. If fi Frequency Dependent and with non-WSS is to de ne time and fre- the transmission is close to surface/ Independent Noise quency dependent scattering functions bottom or there are smaller objects in (Walree et al., 2008). In this paper, the the water, the resulting scatters com- Table 2 presents the possible noise channels considered are WSS. bined with the dominant component in UAC channel. Some of these noise may produce Rician fading. With is frequency independent and can n t farther increase of range and depth, be considered under, 1( ) as Additive SNR Analysis Signal-to-Noise Ratio for WSS scattering effect may be minimal and White Gaussian Noise (AWGN) with Uncorrelated Tap Channel the Rician may become Gaussian zero mean and normal distribution. only fading. In a clear, unobstructed However, some of the noise in Table 2 From the equations (22) through short range and low water column can be frequency dependent, and if the (29), it can be concluded that the received depth channels, there will be dominant operating transmission frequency is as signal in any underwater environment components. But due to the closeness same as the frequencies of any of these of Figure 1 is a summation/combination of the two boundaries and the shorter noise sources, the transmitted signal of Gaussian random variables (RV), range to travel, the scattering com- TABLE 2 ponents will be significant and the scatters will be comparable to the Self and ambient noise in UAC. dominant components, resulting in Rayleigh fading. Figure 5 illustrates Machinery Self-Noise Noise Flow Noise Cavitation this characteristics. (ii) Fading characteristics in deep Pumps, Relative motion Bubble collapse channel: Deep channel transmission reduction gears, between object power plant, and the water will result in Gaussian fading due to etc. the presence of noise, if the transmis- Ambient Noise Hydrodynamic Seismic Biological Ocean traffic sion happens far from surface/bottom boundaries, and the objects in the Movement Movement of Marine life Other boats transmission path are scarce. If however of water earth
110 Marine Technology Society Journal Rician RVs, and Rayleigh RVs. Let the tics. For K ≫ 1, the signal will follow where the mean and the variance of the summation of Gaussian RVs, Rician Gaussian statistics. above SNR will be as follows, RVs, and Rayleigh RVs be denoted as The signal to noise ratio (SNR) can G R RL RVEXP SUM, SUM, and SUM, respectively. be expressed as, μEXP ¼ ; ðσ2 þ N Þ Therefore, the pdf of the received signal otr SignalPower VARðRV Þ will be equal to the pdf of an RV that SNR ¼ σ2 ¼ EXP ð Þ NoisePower EXP 2 38 G R ðσ2 þ Notr Þ is a summation of SUM, SUM,and P ð33Þ j Pathj2 RLSUM or any combination of them. ¼ : NoisePower RVCHI If the RV representing the received sig- μCHI ¼ ; ðσ2 þ Notr Þ nal is denoted by RVREC,then Let the AWGN noise variance and the VARðRV Þ σ2 ¼ CHI ð Þ CHI 2 39 RV ¼ G þ R þ RL ð Þ frequency dependent noise variance be ðσ2 þ Notr Þ REC SUM SUM SUM 30 2 denoted as σ and Notr, respectively. Therefore, (33) can be expressed as Using the values of exponential mean Although RVREC is expressed in (30) and variance and non-central chi-square as summation of Gaussian, Rayleigh, ðjRV jÞ2 mean and variance, equations (38) and SNR ¼ REC ð Þ RVREC 34 or Rician variables, represents σ2 þ Notr (39) become the resultant after the vectorial addition of all paths within symbol duration. λ 1 μEXP ¼ ; Since every path is an i.i.d. Gaussian, or using (19) ðσ2 þ Notr Þ RV the resultant amplitude, i.e., | REC| λ 2 P 2 L 1 2 σEXP ¼ ; ð40Þ will follow any one of Gaussian, ðj l¼ αl ðtÞsðt τl ÞjÞ ðσ2 þ N Þ2 SNR ¼ 0 : ð35Þ otr Rayleigh, or Rician distributions. Rician σ2 þ Notr fading is governed by two parameters, ðK ′ þ λÞ μCHI ¼ ; K, and Ω, which can be expressed as, ðσ2 þ N Þ The eigen and sub-eigen paths will vary otr P in different environments. Hence, the ðK ′ þ λÞ K ¼ d ; ð Þ σ2 ¼ 2 2 ; ð Þ PLL 31 CHI 41 1 P SNR will vary according to each en- ðσ2 þ N Þ2 pi¼1 pi otr vironment. The numerator of (35) will K ′ XLL 1 bethesquareofRayleighorRiceor where > 0 represents the degrees of Ω ¼ Pd þ Ppi; ð32Þ Gaussian variable and the denomina- freedom and λ > 0 represents the rate pi¼1 tor will be the summation of Gaussian in the first equation and noncentrality variance and variance of noise com- parameter in the second equation. P where d represents the power of the ponent, Notr. The square of Rayleigh dominant path, and Ppi, the power of variable gives exponential distribution each less dominant path. Clearly, and the square of Rician variable gives Benefits of Channel when the power of any path is deter- non-chi-square distribution and hence Classification and mined by the transmission loss in (6) can be expressed as RVEXP and RVCHI, α Selection of Channels and by the equation for ,thepath respectively. Therefore, when RVREC is In this section, first, the benefits of R H f powers will depend on , ,and . a Rayleigh or Rician variable, SNR can channel classification will be provided According to the UAC environment, be expressed as SNREXP and SNRCHI briefly and, second, selection of chan- R H f , , will vary resulting in different respectively as shown below. nels will be discussed. values of K and Ω. When K ≂ 0orK ≪
1, the denominator or the sum of RVEXP SNREXP ¼ ð36Þ Benefits of Channel powers of less dominant paths will be ðσ2 þ NotrÞ greater than the power of the domi- Classification nant path, the received signal will fol- It is beneficial to classify the UAC low Rayleigh fading. For K ≥ 1, the RVCHI channels according to their environ- SNRCHI ¼ ð37Þ received signal will follow Rician statis- ðσ2 þ Notr Þ ments. Once the UAC environments
May/June 2013 Volume 47 Number 3 111 are determined, the appropriate chan- is used to differentiate each environ- life concentration may indicate the nel representation can be used. ment and its corresponding channel new UAC environment to be a close In shallow channel environments, equations. For example, the longitude/ to surface channel environment. In close to surface channel may have latitude of location, time of year or sea- such a case, depending on the devia- LOS path (if both the transmitter son, wind velocity will determine the tion of parameter values of the new and receiver are in sight of each other) roughness of the sea surface. Knowing UAC environment from the thresh- arriving first, followed by one time these parameters in addition to the olds of parameter values of a known surface reflected path, then one time transceiver depth from surface will de- UAC environment in the channel data- bottom reflected path, followed by termine if the channel is close to rough base, the in between surface and bottom bottom-surface one time reflected or smooth surface. Once rough sur- environment may be selected. Corre- path, surface-bottom one time reflected face is identified, scatters due to rough spondingly, the channel representation paths, followed by other multiple surface may be taken into account, and for in between surface and bottom can reflected paths. In close to bottom the channel equations corresponding be chosen for communication. channel, the paths will be in the to close to rough surface environment order of LOS, bottom reflected, sur- may be utilized. face reflected, bottom-surface one Simulation Results time reflected path, surface-bottom Selection of Channel Models The simulation is carried out using reflected path followed by other mul- The CI can sense channel envi- the parameters in Table 3, MATLAB, tiple reflected paths. In in-between ronment parameters and map them and the Bellhop model (Porter, 2011) channels, if the difference |zs − zr|is to accurate UAC channel environment usedandprovidedbytheAcTUP small the order of the paths will be according to parameter values (Ahmed software module (Maggi & Duncan, LOS, surface, bottom, surface-bottom & Arslan, 2009a). Once the UAC 2005). one time reflected, bottom-surface one channel environment is determined, The range to depth ratio can define time reflected path followed by multi- the UAC channel environment can be an underwater channel to be shallow ple reflected paths. If the difference mapped (Ahmed & Arslan, 2009b) or deep. A range to depth ratio of |zs − zr|islarge,thepathswillbeLOS, onto any one of the appropriate chan- 10:1 may define a channel as shallow surface, bottom, bottom-surface, nel representations that were presented (Bessios & Caimi, 1994) and the trans- surface-bottom followed by rest of the in the previous sections. mission can be considered horizontal. multiple reflected paths. Once the Channel Representation of Closest The range of transmission can define channel environment and hence Fit: In an event, when the channel data- a channel to be short, medium, or the path origins are identified, it may base does not contain an exact match long. A long-range channel over several be easier to retrieve the signal infor- of a UAC environment, CI can choose tens of kilometers is limited to a few mation. For example, a surface only re- a channel representation that fits kilohertz; a medium-range channel flected path will be affected by surface closest to the UAC environment. over several kilometers has a band- wave and other surface agitations. Thismayhappenwhenasignificant width in the order of tens of kilohertz, Knowledge of path origin will allow number of channel parameters and/or while a short range channel over several applying noise cancellation and small- parametervaluesdefining the spe- tens of meters may have hundreds of scale fading compensation techniques cific UAC environment differ from a kilohertz (Stojanovic, 1996) available. suited for surface boundary agitation. known UAC environment in the data- First, the simulation results of the The UAC channels can be affected base. For example, the depth value in a channel impulse response are presented. by geographical location of commu- new UAC environment may be larger Second, the results of the fading char- nication (longitude/latitude), trans- than the depth threshold for close to acteristics of various channels are mitter and receiver distances from the surface environment in the database, presented. surface and the bottom boundaries, the temperature, and the location in A) Channel Impulse Response water column height, transmission the world may indicate the new envi- in Different UAC Environments range, frequency, sound velocity, the ronment to be in between the sur- ■ Shallow Channel (Constant Sound water environment, etc. Channel param- face and the bottom. But the type of Velocity), Smooth Surface and eters unique to each UAC environment ocean trafficandthetypeofmarine Bottom:
112 Marine Technology Society Journal TABLE 3
Values of depth, transmission distance, transmitter and receiver depth for shallow channel scenario: Long-, medium-, and short-range channels.
Depth (m) Distance (m) Transmitter Depth (m) Receiver Depth (m) Channel Type Frequency (kHz)
1,000 10,000 995 995 Long, Close to bottom 1 5 5 Long, Close to surface 1 5 995 Long, In between 1 100 1,000 95 95 Medium, Close to bottom 10 5 4 Medium, Close to surface 10 5 95 Medium, In between 10 9 90 8.5 8.5 Short, Close to bottom 100 1 1 Short, Close to surface 100 1 8.5 Short, In between 100
In a shallow in between surface close to each other and will be less together, 3H will be grouped together and bottom channel environment, distinct. (using (4)). when the boundaries are smooth, the For short and medium range, if Equations (4) and (6) are used to CIR will contain paths from surface H is higher, multiple boundary re- generate delay and transmission loss only reflection, multiple surface bot- flected paths will be grouped together amplitudes of Figure 15. In this figure, tom reflections, bottom only reflection, and will almost overlap. For example, only the LOS, surface-only, bottom-only, multiple bottom surface reflections, paths resulting from 2H will be grouped bottom-surface, and surface-bottom and paths due to other reflections/ refractions/scatters from in between objects as in (10). The CIR of in be- FIGURE 6 tween channels in Figures 8, 11, and Short range, close to surface, shallow channel (smooth surface and bottom): transmission loss/ 14 contain all these groups of paths. amplitude at various delays and at various ranges, depth = 9 m, transmission distance = 90 m, Figures 6, 9, and 12 illustrate frequency = 100 kHz. close to smooth surface channels. If the paths reflected from the bottom are weak, they can be neglected. Fig- ures 7, 10, and 13 illustrate close to smooth bottom channels. If the paths reflected on the surface are weak, they can be neglected. In close to surface smooth chan- nels, the values of source depth zs and receiver depth zr will be smaller com- pared to water column height H or transmission range D.WhenbothH and D are small, in case of short range, the paths LOS, surface only, bottom- only, bottom-surface, surface-bottom, paths will be more distinctly apart from each other. If D is high as in long-range channels, the above paths will arrive
May/June 2013 Volume 47 Number 3 113 FIGURE 7 FIGURE 9
Short range, close to bottom, shallow channel (smooth surface and Medium range, close to smooth surface, shallow channel (smooth bottom): transmission loss/amplitude at various delays and at various surface and bottom): transmission loss/amplitude at various delays ranges, depth = 9 m, transmission distance = 90 m, frequency = 100 kHz. and at various ranges, depth = 100 m, transmission distance = 1,000 m, frequency = 10 kHz.
FIGURE 8 FIGURE 10 Short range, in between smooth surface and smooth bottom, shallow channel (smooth surface and bottom): transmission loss/amplitude at Medium range, close to smooth bottom, shallow channel (smooth various delays and at various ranges, depth = 9 m, transmission distance = surface and bottom): transmission loss/amplitude at various delays 90 m, frequency = 100 kHz. and at various ranges, depth = 100 m, transmission distance = 1,000 m, frequency = 10 kHz.
114 Marine Technology Society Journal FIGURE 11 FIGURE 13
Medium range, in between smooth surface and smooth bottom, shallow Long range, close to smooth bottom, shallow channel (smooth surface channel (smooth surface and bottom): transmission loss/amplitude and bottom): transmission loss/amplitude at various delays and at at various delays and at various ranges, depth = 100 m, transmission various ranges, depth = 1,000 m, transmission distance = 10,000 m, distance = 1,000 m, frequency = 10 kHz. frequency = 1 kHz.
FIGURE 12
Long range, close to smooth surface, shallow channel (smooth surface and bottom): transmission loss/amplitude at various delays and at various ranges, depth = 1,000 m, transmission distance = 10,000 m, FIGURE 14 frequency = 1 kHz. Long range, in between smooth surface and smooth bottom, shallow channel (smooth surface and bottom): transmission loss/amplitude at various delays and at various ranges, depth = 1,000 m, transmission distance = 10,000 m, frequency = 1 kHz.
May/June 2013 Volume 47 Number 3 115 paths are displayed. For short range chan- Compared to the short range chan- lays in Figures 6, 9, and 12 will vary. nel (a), D is small and H is small, hence nels, the medium range channel paths This variation will be more prominent the LOS and surface only paths are are much less spread out and are al- in short and medium range channels. distinct. For medium-range (b) and most overlapping, and are arriving as For a varying bottom, the number long-range (c) channels, both D and an overlapped bundle at each delay. of paths, their amplitudes, and delays H are high and these two paths almost This can be observed in Figures 9, 10, inFigures7,10,and13willvary. overlap each other. Paths interacting and 11. In long-range channels, the This variation will be more prominent with the bottom boundary arrive later neighboring paths completely overlap in short- and medium-range channels. but these paths are close to the LOS each other. As a result, at each delay, ■ Deep Channel Simulation (Varying and surface only reflected paths in there is only one path instead of spread- Sound Velocity Profile): terms of loss and delay and hence cannot ing of paths. Figures 12, 13, and 14 Sound velocity will vary in a deep be neglected. If zs and zr are small illustrate this. channel. Considering a variable sound enough and H and D are large enough, In the shallow channel environ- velocity profile simulation can be car- the paths interacting with the bottom ments presented above, the paths in dif- ried out in SOFAR and other deep will have larger delay and loss and hence ferent groups arrive very close to each channels. Simulation results will be can be neglected as seen in equation (13). other. Because of this reason, the paths similar to that of the shallow channel In a short range, shallow, close in different groups are not separately figures as presented above. Because of to smooth surface channels,asin shown in the figures. high depth and long range that charac- Figure 6, the paths are more spread ■ Shallow Channel (Constant Sound terize the deep channels, there will be out at each delay, i.e., at each delay, Velocity), Rough Surface and high loss associated with each path ar- neighboring paths arrive without over- Bottom: riving at very long delays. lapping. In Figure 8, short range, in If the bottom or the surface varies in B) Fading Characteristics of between surface and bottom channel, shallow channels, the power delay pro- WSS Uncorrelated Tap Channel the paths are less spread out compared file varies drastically, where only a few In Figure 16, the power (power to closed to surface case. In a close to paths arrive at the receiver at different calculated in terms of path loss) ratios bottom channel, as in Figure 7, the delays and at different power levels. of direct path to other paths, in various paths are least spread out among the For a varying surface, the num- ranges, in shallow water close to bot- three short range channels. ber of paths, their amplitudes, and de- tom channels are illustrated. The power
FIGURE 15
Shallow channel, close to surface (smooth surface and bottom): trans- FIGURE 16 mission loss at various delay. (a) Depth = 9 m, distance = 90 m, transmitter depth = 1 m, receiver depth = 1 m, frequency = 100 kHz. (b) Depth = 100 Top: Short range, close to bottom, shallow channel; Middle: Medium range, m, distance = 1,000 m, transmitter depth = 5 m, receiver depth = 4 m, close to bottom, shallow channel; Bottom: Long range, close to bottom, frequency = 10 kHz. (c) Depth =1,000 m, distance = 10,000 m, trans- shallow channel. mitter depth = 5 m, receiver depth = 5 m, frequency = 1 kHz.
116 Marine Technology Society Journal values are taken from Figures 7, 10, References Maggi, A., & Duncan, A. 2005. Underwater and 13. All the arrived paths are con- Ahmed, S., & Arslan, H. 2009a. Cognitive acoustic propagation modeling software-actup sidered. In medium- and long-range intelligence in UAC channel parameter v2.2l. Center for Marine Science and Technology channels, the ratio is greater than 1 at identification, measurement, estimation, and (CMST). January 25, 2012. environment mapping. In: Proc. MTS/IEEE all three distances, indicating Rician or Morozov, A.K. 1995. The sequential analysis Oceans. Bremen, Germany. doi: 10.1109/ Gaussian fading. At 6,000 m in long application in the problem of estimation OCEANSE.2009.5278161. range and at 600 m in medium range, of stochastic channel impulse response. it is Gaussian fading. At 3,000 m in Ahmed, S., & Arslan, H. 2009b. Cognitive In: Proc. MTS/IEEE Oceans. San Diego, CA. long range and at 200 m in medium intelligence in the mapping of underwater doi: 10.1109/OCEANS.1995.528570. acoustic communication environments to range, it is also Gaussian fading. At Porter, M.B. 2011. The bellhop manual and channel models. In: Proc. MTS/IEEE Oceans. longer distances, the direct path loses user’s guide: Preliminary draft. Heat, Light, Biloxi, Mississippi, USA. power significantly and becomes com- and Sound Research, Inc. May 30, 2012. parable to the less dominant paths. Appleby, S., & Davies, J. 1998. Time, Socheleau, F., Laot, C., & Passerieux, J. Hence at 1,000 m in medium and at frequency and angular dispersion modeling 2011. Stochastic replay of non-WSSUS under- in the underwater communications channel. 10,000 m in long range channels, water acoustic communication channels In: Proc. MTS/IEEE Oceans. Nice, France. it becomes Rician fading. In short recorded at sea. IEEE Trans Signal Process. doi: 10.1109/OCEANS.1998.724318. range channels, the indirect paths 59(10)4838-49. http://dx.doi.org/10.1109/ fi have signi cant power and hence re- Bessios, A., & Caimi, F. 1994. Multipath com- TSP.2011.2160057. sults in mostly Rayleigh fading at all pensation for underwater acoustic communica- Stojanovic, M. 1996. Recent advances in three distances. tion. In: Proc. MTS/IEEE Oceans. Brest, France. high-speed underwater acoustic communica- doi: 10.1109/OCEANS.1994.363905. tions. IEEE J Ocean Eng. 21(2):125-36. Conclusion Bjerrum-Niese, C., & Lutzen, R. 2000. http://dx.doi.org/10.1109/48.486787. Stochastic simulation of acoustic commu- Once the UAC environments are Walree, P., Jenserud, T., & Smedsrud, M. nication in turbulent shallow water. IEEE J determined from the channel parameters, 2008. A discrete-time channel simulator driven Ocean Eng. 25(4)523-32. doi: 10.1109/ the channel representations can be de- by measured scattering functions. IEEE J 48.895360. rived according to the environments. Selected Areas Commun. 26(9)1628-37. In this paper, a high level classification Byun, S., Kim, S., Lim, Y., & Seong, W. of the UAC channel environments are 2007. Time-varying underwater acoustic presented and channel representations channel modeling for moving platform. are proposed, which are derived accord- In: Proc. MTS/IEEE Oceans. Vancouver, BC. ing to the classified UAC environments. doi: 10.1109/OCEANS.2007.4449361. The channel analysis is shown in terms Galvin, R., & Coats, R. 1996. A stochastic of channel impulse response equations underwater acoustic channel model. In: Proc. and fading characteristics of the received MTS/IEEE Oceans. Fort Lauderdale, FL. signals. As part of future research, cor- doi: 10.1109/OCEANS.1996.572599. related taps and non-WSS channels Geng, X., & Zielinski, A. 1995. An eigenpath can be considered. underwater acoustic communication channel model. In: Proc. MTS/IEEE Oceans. San Diego, Authors: CA. doi: 10.1109/OCEANS.1995.528591. Sadia Ahmed Gutierrez, M.A.M., Sanchez, P.L.P., & Neto, Huseyin Arslan J.V.V. 2005. An eigenpath underwater acoustic Department of Electrical Engineering, communication channel simulation. In: Proc. University of South Florida, MTS/IEEE Oceans. Washington, DC, USA. 4202 East Fowler Avenue, doi: 10.1109/OCEANS.2005.1639788. ENB 118, Tampa, FL 33620 Lurton, X. 1996. An Introduction to Email: [email protected]; Underwater Acoustics: Principles and [email protected] Applications. UK: Springer.
May/June 2013 Volume 47 Number 3 117 PAPER Wrecks on the Bottom: Useful, Ecological Sentinels?
AUTHOR ABSTRACT Andrea Peirano Wrecks play an important role in enhancing marine biodiversity. SCUBA diving ENEA-Marine Environment video-samplings were performed on eight wrecks, including seven shipwrecks and Research Centre, La Spezia, Italy a sunken airplane, scattered over 180 km along the Ligurian coastline in the north- western Mediterranean Sea, in water depths of 30–65 m. Differences in composi- tion of macrobenthic communities were found to be related to the bottom Introduction sedimentology and the composition and geometry of the investigated structures. fl Ostrea recks are artificial habitats that The iron, at, and even substrata of shipwrecks were dominated by Bivalvia ( edulis Corynactis viridis may enhance marine biodiversity ) and Anthozoa ( ), whereas the aluminum, cage-like struc- W ture of the airplane was dominated by massive sponges and bryozoans. Further- (Baine, 2001; Svane & Petersen, 2001; Massin et al., 2002; Mallefet et al., more, abundances of some macrobenthic invertebrates were greater on the 2008). Their geometrical complexi- wrecks than those observed on natural, rocky substrates. Because of the increasing ties, structures, and textures provide popularity of use of video and photo digital apparatuses among recreational divers, fi suitable substrates for settlements combined with wreck resistance to corrosion, arti cial geometries and available ’ of several benthic species (Svane & surfaces that facilitate species settlement and growth, data from wrecks consisting Petersen, 2001). On soft bottoms, of images and related metadata (depth, date, water temperature, etc.) could provide wrecks especially play an important a new opportunity for monitoring Mediterranean marine biodiversity. fi role by offering suitable surfaces Keywords: wrecks, macrobenthos, video-sampling, CCR scienti c diving for the larve of benthic organisms, which otherwise would not be able to settle. Because of the function and use of ity are ships that were sunk during Given their importance as promot- these artificial structures, however, World War II. Airplanes that were ers of marine biodiversity, old ships the presence of pollutants, such as lost in the war often have been de- and sunken oil and gas platforms, heavy metals in cables and paints stroyed and dispersed by trawlers. both of which have become popular and oil and explosive residuals (Church The interest in Italian wrecks has gen- as dive attractions, have been included et al., 2007) may be found within erally come from archeologists because within Marine-protected areas (MPA) their compartments. Thus, before of their importance as sites of national of the world (Bonshack & Sutherland, being eligible to be positioned inten- heritage (http://www.archeomar.it). 1985; Baine, 2001; Walker et al., tionally on the seabed, these struc- However, except for a few general 2007; Kaiser & Kasprzak, 2008). tures should be cleaned and treated observations, the importance of the World War II ships are the most com- to remove any pollutant representing Ligurian wrecks as a possible promoter mon and best preserved wrecks be- serious threat to marine life. Further- of Mediterranean marine biodiversity cause of the thickness of their hulls more, their scuttling should be limited has not been taken into account. and the armoring of their superstruc- by appropriate regulations (Bell et al., The aim of the present work is to tures. Moreover, some of them have 1997; Helton, 2003). analyze and compare the characteris- been included on lists of archaeological On the Ligurian Sea seabed in the tics and composition of macrobenthic importance to ensure that their histor- northwest Mediterranean Sea, more communities colonizing eight wrecks, ical importance is passed on to future than 50 wrecks were found along taking into account the structural ge- generations (UNESCO, 2001; Church the coastline in water depths of 20– ometry, composition, and texture of et al., 2007; Wessex Archaeology 100 m (Carta, 2000; Carta et al., the materials composing the wrecks. Limited, 2008; Underwood, 2009). 2008; Mirto et al., 2009). The major- Comparisons between macrobenthic
118 Marine Technology Society Journal taxa on wrecks with those living on artificial structures, only those lying FIGURE 2 neighboring natural substrates also between 30 and 65 m in depth were Equa fl Exploring the wreck of the using the were made to elucidate factors in u- taken into account to reduce the im- mixed-gas closed-circuit rebreather (CCR) encing colonization and the wrecks’ pact caused by wave action and the apparatus APD Inspiration®. role in contributing to coastal com- seasonal thermocline. Seven of the munity richness and conservation. eight wrecks investigated were ships; Thewrecksastoolsformonitoring six were iron ships that sank between marine biodiversity are discussed. 1917 and 1967 (Mohawk Deer, Genova, Marcella, Vittoria, Equa, Concordia)and onewasawoodenship(theCycnus) Material and Methods sunkin1981.Theotherwreck,the Study Site BR.20, was an Italian bomber shot SCUBA video surveys were per- down near Imperia in 1941. The Cycnus formed in 2008–2009 on eight and the bomber were situated Posidonia “wrecks” lying on the Ligurian seabed on sandy bottoms close to (Figure 2). Compared to an open- oceanica (Figure 1), scattered over 180 km along seagrass beds (Bianchi & circuit (OC) apparatus, CCR allowed the coastline. The Liguria region is Peirano, 1995). One of the iron ships, dives at greater depths with longer Mohawk Deer dominated by a large and well-defined the , lay on a detritic sea- stays and a reduced number and dura- anticlockwise circulation and by bio- bed with the bow against a rocky wall tion of decompression stops (Parrish diversity hot spots promoted by the dominated by a rich coralligenous as- & Pyle, 2002). A Sony full-HD presence of a coralligenous commu- semblage. The other shipwrecks were (1,920 × 1,080 pixels) video camera nity, usually growing below 25 m in positioned on muddy bottoms. was enclosed in an underwater housing depth (Cattaneo-Vietti et al., 2010). with a wide-angle lens and two lamps With the purpose of analyzing only Video-Sampling (50 W each). A frame (25 × 25 cm) was fi mature communities, wrecks that sank The videos were taped by means of xed on the camera at distance of 30 or more years ago (Perkon-Finkel SCUBA diving performed using a 30 cm (Figure 3). Short videos (video et al., 2006; Relini et al., 2007) were mixed-gas, closed-circuit rebreather clips) were shot at random in different selectedforthisstudy.Amongthese (CCR) apparatus APD “Inspiration” parts of each wreck, as hull, cranes, and ® propeller, etc. In the laboratory, videos
FIGURE 1 FIGURE 3 Wrecks’ distribution along the Liguria region. 1 = Cycnus, 2 = BR.20 Bomber, 3 = Mohawk Deer, 4=Genova,5=Marcella,6=Vittoria,7=Equa,8=Concordia. One video image from the Concordia star- board side of the ship, colonized by Ostrea edulis and Corynactis viridis (dark points). During the video shootings, the frame allowed the diver to maintain the video camera per- pendicular to and at a fixed distance from the surface.
May/June 2013 Volume 47 Number 3 119 were analyzed, and for each wreck, Results vermilara, Flabellia petiolata and Goio- several variables, divided in different A minimum dive-time of 20 min cladia sp. clustered around the center categories, were evaluated. Data on allowed a careful exploration of each of the PCA diagram were only found depth range (30–40 m, 40–50 m, wreck. The resulting high-definition occasionally. The aluminum hull 50–60 m), bottom/seabed (sediment) (HD) videos extracting single frames of the BR.20 bomber was dominated type (1 = sand, 2 = mud, 3 = detritic, (maximum resolution of about 5 mega- by sponges (Dictyoceratida sp. 2, 4 = rock), wreck zone (1 = internal, 2 = pixels each) guaranteed suitable images Aplysina aerophoba), and one bryozoan external), wreck material (1 = wood, for identifying macrobenthic species (Celleporidae sp.) was found (Fig- 2 = iron, 3 = aluminum), surface tex- more than 1 cm in size. Macrobenthic ure 4a); see the lower left quadrant of ture(1=even,2=rough,3=grid-like, species were classified at species or the PCA diagram. The scatterplot of 4 = with cracks), geometrical shape family level. A total of 35 macrobenthic row scores (wrecks) confirmed the of the structure (1 = round, 2 = flat, organisms (7 Algae, 11 Porifera, ordination of variable; almost all taxa 3 = angular, 4 = complex), and struc- 9Anthozoa,1Bivalvia,2Anellida, growing on the BR.20 bomber were ture slope (1 = horizontal, 2 = subhori- 4 Bryozoa) were identified (Table 1). grouped in the lower left quadrant zontal,3=vertical,4=overhanging) Principal component analysis (Figure 4b). fi were extracted from each video clip. (PCA) revealed that the first two com- The three types of seabed identi ed Among benthic organisms found ponents were both significant: the first during the present study were mud on the wrecks, only the long-living (PC1) explained 10.5 % of the vari- with >88 % of fines and sand and det- macrobenthic taxa were considered ance, the second (PC2) explained ritic seabed each with <10 % of fines. in the present study because of their 7.9 %. (Figures 4a and 4b). The anal- Fines included clay + silt following multiannual lifespan of colonization. ysis of the variable importance, rep- Bertolotto et al. (2005). Neither the Taxonomical identification of the resented in Figure 5, showed that amount of fines (R = −0.14; p > 0.05) macrobenthic species was facilitated species ordination was mainly related nor the distance of the wrecks from by using HD digital video softwares to the type of the bottom (muddy bot- the coast (R =0.23,p > 0.05) were cor- (Picture Motion Brower® by Sony toms vs. detritic/sandy bottoms) and related with the number of species and Media Player Classic® by Gabest). to the type of material composing the found. Macrobenthic species abundance was wreck (aluminum vs. iron). Hence, Data collected on “wrecks” were evaluated in terms of cover on still- variables were divided into two main compared with those extracted from frames selected randomly from each groups, represented on the right and the literature and referring to natural video clip. The minimum surface ana- on the left sides of the PCA diagram substrata (Figure 6). An increase in lyzed in each video clip was 1 m2. The respectively (Figure 4a). Flat and verti- the number of different benthic spe- total abundance of a species was esti- cal surfaces of the iron shipwrecks, cies on natural substrata was found mated following semiquantitative lying on muddy bottoms, were charac- from the Western to Eastern side of scale adopted in cover visual estimation terized by the highest cover of the bi- the Ligurian coast. In contrast, the (Boudouresque, 1971; Kenchigton, valve Ostrea edulis and the anthozoan number of species colonizing wrecks 1978; Bianchi et al., 2004; Work Corynactis viridis, reaching the 90% showed a weak negative trend from et al., 2008): <1% = rare, 1–10% = of cover (Figure 4a). Subhorizontal, west to east. In the cases of the Mohawk present, 10–50% = abundant, > 50% = overhanging rough structures favored Deer (114 %) and Genova (111%), spe- very abundant. The resulting matrix settlement and growth of low-light tol- cies abundances were higher than those (wrecks × variables) was analyzed by erant species such as the anthozoans recorded on the nearby natural sub- using the principal component analysis Paramuricea clavata, Leptopsamia strates (Table 2). (PCA). pruvoti, Eunicella cavolinii, bryozoans Data on species abundance re- (Aedonidae spp.), serpulids, and red corded on wrecks were compared encrusting algae (Corallinales spp.), as Discussion with those collected with video and/or shown in the upper right side of the The combination of close-circuit photo sampling on natural substrata diagram (Figure 4a). In contrast, rebreather (CCR) diving with high- nearby. Differences between wrecks other species such as Caulerpa racemosa definition (HD) video shooting was and natural substrata were examined. v. cylindracea, Chartella sp., Codium useful in the deep-diving surveys. As
120 Marine Technology Society Journal TABLE 1
List of species found on wrecks. Wreck numbers are referred to Figure 1. Numbers for bottom type, material structure, surface typology and slope are reported in material and methods.
Wreck number 12345678
Distance from the coast (nm) 0.5 1.5 0 1 0.9 8.6 2.5 14 Video samples (n) 5 12 16 9 12 10 8 7 Depth range (m) 35–38 46 30–46 52–55 42–60 35–38 38–40 40–42 Bottom type 14422222 Wreck zone 1 1 1–211111 Material 1–22–3222222 Surface texture 1–2–41–2–3–41–21–2–3–41–21–3–41–2–31–3 Structure shape 1–2–31–2–3–41–2–31–2–3–41–2–3–41–2–31–2–3–41–2–3 Structure slope 1–2–31–2–31–2–3–41–2–32–3–41–3–41–2–31–3 Algae 1 Corallinales sp.1 + + + + 2 Corallinales sp.2 + 3 Gloiocladia sp. + 4 Peyssonellia sp. + 5 Caulerpa racemosa + 7 Codium vermilara + 8 Flabellia petiolata + Porifera 9 Haliclona sp. + 10 Dictyoceratida sp.1 + + 11 Dictyoceratida sp.2 + 12 Dysidea sp. ++ ++ 13 Aplysina aerophoba +++ 14 Porifera indet. sp.1 + + 15 Porifera indet. sp.2 + + + + + + 16 Porifera indet sp.3 + + 17 Porifera indet sp.4 + 18 Porifera indet sp.5 + + + + + + 19 Porifera indet sp.6 + Anthozoa 20 Eunicella cavolinii + 21 Eunicella singularis + 22 Eunicella verrucosa ++ + 23 Leptogorgia sarmentosa ++ + 24 Paramuricea clavata + continued
May/June 2013 Volume 47 Number 3 121 TABLE 1
Continued
Wreck number 1 2 3 4 5678
25 Corynactis viridis ++++ 26 Balanophyllia europaea ++ + 27 Leptpsammia pruvoti + 28 Phyllangia sp. + Bivalvia 29 Ostrea edulis + ++++++ Anellida 30 Sabella spallanzanii ++ 31 Serpulidae spp. + + + Bryozoa 32 Aedonidae sp. + + 33 Watersiporidae sp. + 34 Celleporidae sp. + + 35 Chartella sp. + a noninvasive sampling method, circuit (OC) diving apparatus that en- find any differences between the two video-sampling had no impact on the hances turbidity during video shooting methods when photographs had a sig- investigated organisms. The only pos- on vertical and below overhanging nificant area coverage and adequate sible disturbance from sampling was structures, was drastically reduced by resolution. The video procedure used the bioturbation effect that was pre- the use of CCR. By comparing visual in the present work assured the anal- vented by using CCR. Bubble emis- and photo-sampling on macrobenthic ysis of a minimum area larger than sion during the diver’s exhalation, organisms of Mediterranean hard sub- 0.25 m2, in accordance with methods normally occurring with the open strates, Parravicini et al. (2009) did not suggested for the sampling of Mediter- ranean hard bottoms and artificial sub- FIGURE 4 strata such as artificial reefs (Weinberg 1978; Bianchi et al., 2004, Relini PCA of the loading factors between principal components axis (PC1 and PC2): a) scatterplots of 2004; Parravicini et al., 2009), while categorical variable categories (depth, bottom type, wreck material, and structure characteristics) and continuous variables (species); b) scatterplots of wrecks’ scores. Wrecks and species num- HD resolution proved its potential in fi bers are reported in Table 1. species identi cation. In the present study, PCA analysis revealed that bottom type is fun- damental in epibenthic coloniza- tion of wrecks and it has a key role in determining marine community struc- tures. A connection between species occurrence and sediment typology is in agreement with findings of Zintzen et al. (2008) and Guerin (2009), who showed a relationship among epifaunal communities on wrecks and oil plat- forms, and the bottom sediment of
122 Marine Technology Society Journal FIGURE 5 in Liguria that wooden barges and shipwrecks were less appropriate for Plot of variable importance in scatterplot of Figure 4. Variable importance varies from a maximum (1) on the left to a minimum (0) on the right. colonization, in agreement with video shot on the Cycnus. Iron structures of wrecks are usually damaged by corro- sion, which first attacks the thinnest parts (Relini et al., 2007) and at the end, may contribute to the collapse of the whole structure (Bell et al., 1997). This damage is enhanced by bubbles emitted by SCUBA open- circuit apparatus and by chains used to anchor diving buoys. The illegal predation of wrecks further contrib- uted to their destruction (UNESCO, 2001; Tilburg, 2006). Videos of this study showed that the aluminum on the aircraft BR-20 and the massive structures such as the propellers, cranes and portholes of the iron ships were to be the most resistant materials to the effects of corrosion. theBalticSea.InLiguriathisisalso and artificial substrata such as con- Studying wrecks in the North Sea, true for natural, rocky bottoms where crete, rocks, ceramic, and earthenware Australia and Red Sea, Guerin (2009), littoral photophilic communities are material demonstrated that species Walker et al. (2007) and Perkol-Finkel influenced by substratum mineralogy recruitment and survival were strictly et al. (2005, 2006) also agreed that the (Cattaneo-Vietti et al., 2002). dependent on the substrate-type geometrical complexity of wreck struc- Also, wreck material is fundamen- (Burt et al., 2009; Perkol-Finkel & tures plays a key role in determin- tal in macrobenthos colonization. Ex- Benayahu, 2006; Antoniadou et al., ing species colonization. On muddy periments comparing natural habitats 2010). Relini et al. (2007) showed bottoms of the Ligurian Sea, ver- tical surfaces of studied shipwrecks were dominated by Ostrea edulis and FIGURE 6 Corynactis viridis. The cage-like struc- Number of species found on wrecks (present work) versus nearby natural substrata (from Peirano ture of the bomber BR-20 probably & Sassarini, 1991; Cocito et al., 2002; Cattaneo-Vietti, 2004). limited sediment accumulation by al- lowing enough water circulation to re- move sediments. These environmental conditions determined the settle- ment and colonization of Porifera and Bryozoa, and the two taxa became the dominant filter-feeders colonizing the airplane remnants. Wrecks are not only devices for at- tracting divers but play an important role in increasing production normally associated with bare bottoms (mud and sandy) (Svane & Petersen, 2001; Massin et al., 2002; Church et al.,
May/June 2013 Volume 47 Number 3 123 124 aieTcnlg oit Journal Society Technology Marine
TABLE 2
Comparison among taxa composition of macrobenthic assemblages found on wrecks studied in the present work (pw) and those reported on natural substrata in nearby sites in previous papers (1 = Cattaneo-Vietti, 2004; 2 = Peirano & Sassarini, 1991; 3 = Cocito et al., 2002).
Reference number pw pw pw (1) pw (1) pw pw (2) pw (2) pw (3)
area Imperia Imperia Camogli Camogli Paraggi Paraggi Framura Framura P. Mesco P. Montenero P. Montenero La Spezia La Spezia Wreck/sample 1 2 3 P0C 4 C4 5 6 – 7 – 8 – number Method Video Video Video Photo Video Photo Video Video Photo Video Photo Video Photo Depth range (m) 30 46 30–46 24–33 30–52 12–16 42–60 38 18–27 38 18–27 42 15–24 Bottom (sediment) 133424224 2 4 2 4 type Samples (n) 5 12 16 10 9 10 12 10 7 8 4 7 30 Taxa Algae 1 1 4 4 6113 2 4 1 10 Spongiae 2 3 2 2 6 197123 7 4 23 Anthozoa 1 6 5 1 2417 1 4 4 13 Bivalvia 1 1 1 1 1 1 1 Anellida 1 1 1 2 1 3 Bryozoa 1 1 2 3 1 1 2 1 9 Ascidiacea 211 Species (n) 6 6 16 14 10 9 17 11 27 7 17 10 59 Wrecks vs. natural - - 114 111 63 41 41 17 habitat (%) 2007; Mallefet et al., 2008). Their with previous ones taped 13 years be- References importance in the Ligurian Sea was fore by recreational divers, in the same Antoniadou, C., Voultsiadouì, E., & previously highlighted by Relini et al. areas of the wreck a reduction in the Chintiroglou, C. 2010. Benthic colonization (2007). The author analyzed 15 years number of the gorgonians Eunicella and succession on temperate sublittoral rocky of benthos colonization on artificial cavolinii and Paramuricea clavata was cliffs. Est Coast Shelf Sci. 82:426-32. reefs along the Ligurian coast con- evidenced. These observations could Baine, M. 2001. Artificial reefs: a review of cluding that the concrete blocks acted be related with the mortality event their design, application, management and in the same way as natural, rocky bot- that affected the gorgonian species liv- performance. Ocean Coast Manage. 44:241-59. toms. Data from the present work ing on natural rocky walls in the late http://dx.doi.org/10.1016/S0964-5691(01) showed that the abundance of macro- summer 1999 (Cerrano et al., 2000). 00048-5. benthos on shipwrecks may be similar In order to heighten the general aware- Bell, M., Buchanan, M., Culbertson, J., and, in some cases, greater than that ness of the ecological and historical Dodrill, J., Kasprzak, R., Lukens, R., & found on natural substrates. These importance of wrecks and to obtain Tatum, W. 1997. Guidelines for marine findings are in agreement with the low-cost data on their associated biodi- artificial reef materials. Artificial Reef Subcom- observations of Perkol-Finker et al. versity, ‘wreck monitoring programs’ mittee of the Technical Coordinating (2006), which reported values for involving recreational divers should Committee, Gulf States Marine Fisheries epifaunal colonization on a shipwreck be promoted (UNESCO, 2001; Commission. Ocean Springs: Gulf States similar to those found on neighboring Wessex Archaeology Limited, 2008; Marine Fisheries Commission office. 118 pp. natural bottoms in the Red Sea. More- Underwood, 2009). The increasing Bertolotto, R.M., Tortarolo, B., Frignani, M., over, Church et al. (2007), studying interest in wrecks, mainly due to the Bellucci, L.G., Albanese, S., Cuneo, C., … an historical shipwreck in the Gulf of spread of high technology diving Gollo, E. 2005. Heavy metals in surficial Mexico, showed not only that the epi- equipment and low-cost HD photo- coastal sediments of the Ligurian Sea. Mar benthos of the artificial structure was graphic and video apparatuses, com- Pollut Bull. 50:344-59. http://dx.doi.org/ richer than that of the surrounding bined with the use of the Internet 10.1016/j.marpolbul.2004.12.002. natural areas, but also that it could be asasourceofinformationexchange, Bianchi, C.N., & Peirano, A. 1995. Atlante the source for the colonization of the delivers possibilities to easily gain eco- delle Fanerogame marine della Liguria: Posidonia neighboring substrata. logical data that will considerably oceanica e Cymodocea nodosa. La Spezia: Enea- Because of their role as historical help scientists in monitoring marine Centro Ricerche Ambiente Marino. 146 pp. attractions for recreational divers, ship- biodiversity. wrecks could become good “sentinels” Bianchi, C.N., Pronzato, R., Cattaneo-Vietti, R., … of biological changes affecting marine Benedetti-Cecchi, L., Morri, C., Pansini, M., Bavestrello, G. 2004. Mediterranean marine environments. Large surfaces of ship- Acknowledgments benthos: a manual of methods for its study and wrecks may favor, for example, inva- The author is grateful to his friend sampling. Biol Mar Medit. 10(1):185-215. sive species colonization, as observed and rebreather instructor G. Paparo by Work et al. (2008) in the Central for his assistance during the dives on Bohnsack, J.A., & Sutherland, D.L. 1985. Pacific and by Perkon-Finkel et al. wrecks, to his colleagues C. Lombardi Artificial reef research: a review with recom- (2006) in the Red Sea. In this study, and S. Cocito for their help with mendations for future priorities. Bull Mar Sci. the presence of the green alga Caulerpa bryozoan taxonomy and the critical 37(1):11-39. racemosa var. cylindracea, one invasive comments on the manuscript, and to Boudouresque, C.F. 1971. Méthodes d’étude species that colonized almost all the E. Taylor, A. Jochens, and N. Lucey for qualitative e quantitative du benthos (en parti- Mediterranean coasts in one decade their suggestions and language revision. culier du Phytobenthos). Tethys. 3(1):79-104. (Piazzi et al., 2005), was recorded on Mohawk Deer Burt, J., Bartholomew, A., Bauman, A., Saif, A., the shipwreck. & Sale, P.F. 2009. Coral recruitment and early Massive wreck structures such as Author: benthic community development on several propellers or cranes, which are more Andrea Peirano materials used in the construction of artificial resistant to deterioration, are easily rec- ENEA-Marine Environment Research reefs and breakwaters. J Exp Mar Biol Ecol. ognizable in monitoring studies. By Centre, C.P. 224, La Spezia (Italy) 373:72-8. http://dx.doi.org/10.1016/j.jembe. comparing video of the Mohawk Deer Email: [email protected] 2009.03.009.
May/June 2013 Volume 47 Number 3 125 Carta, E. 2000. Navi e relitti tra Montecarlo e Cocito, S., Bedulli, D., & Sgorbini, S. 2002. Parrish, F.A., & Pyle, R.L. 2002. Field com- il promontorio di Portofino. Rapallo: Azienda Distribution patterns of the sublittoral parison of open-circuit SCUBA to closed-circuit grafica Busco editrice. 143 pp. epibenthic assemblages on a rocky shoal in the rbreather for deep mixed-gas diving operations. Ligurian Sea (NW Mediterranean). Sci Mar. Mar Technol Soc J. 30(2):13-22. http://dx.doi. Carta, E., Maggiori, A., & Penco, A. 2008. 66(2):175-81. org/10.4031/002533202787914052. Navi e relitti tra Sestri Levante e la Spezia. Rapallo: Azienda grafica Busco editrice. 143 pp. Guerin, A.J. 2009. Marine Communities of Peirano, A., & Sassarini, M. 1991. Analisi North Sea Offshore Platforms, and the Use of delle caratteristiche distributive di alcune facies Cattaneo-Vietti, R., Albertelli, G., Bavestrello, Stable Isotopes to Explore Artificial Reef Food di substrato duro dei fondali delle Cinque G., Bianchi, C.N., Cerrano, C., Chiantore, Webs. Thesis for the degree of Doctor of Terre (Mar Ligure). Oebalia. 17(2):523-8. M., … Schiaparelli, S. 2002. Can rock com- Philosophy University of Southampton, Fac- position affect sublittoral epibenthic com- Perkol-Finkel, S., & Benayahu, Y. 2006. The ulty of Engineering, Science and Mathematics. munities? PSZNI: Mar Ecol. 23(1):65-77. role of differential survival patterns in shaping Southampton: School of Ocean and Earth http://dx.doi.org/10.1111/j.1439-0485.2002. coral communities on neighboring artificial Sciences. 226 pp. tb00008.x. and natural reefs. J Exp Mar Biol Ecol. Helton, D. 2003. Intentional scuttling 369:1-7. http://dx.doi.org/10.1016/j.jembe. Cattaneo-Vietti, R. 2004. Progetto di studio of vessels as a response alternative. IOSC 2008.09.016. per la valutazione e valorizzazione delle emer- papers, 420:1-15. http://www.iosc.org/papers/ genze naturalistiche dell’Area Naturale Marina IOSC%202003%20a272.pdf. Perkol-Finkel, S., Shashar, N., Barnea, O., Protetta del Promontorio di Portofino. Parte I: Ben-Daviv-Zaslaw, R., Oren, U., Reichart, T., … Valutazione della struttura delle principali Kaiser, M.J., & Kasprzak, R.A. 2008. The Benayahu, Y. 2005. Fouling reefal commu- cenosi presentinell’area anche allo scopo di impact of the 2005 hurricane season on the nities on artificial reefs: does age matter? definirne la ricchezza specifica (biodiversità). Louisiana Artificial Reef Program. Mar Policy. Biofouling. 21:127-40. http://dx.doi.org/ Relazione finale. Genova: URL-CoNISMa- 32:956-67. http://dx.doi.org/10.1016/j.marpol. 10.1080/08927010500133451. Università degli Studi di Genova - Dipteris. 2008.02.006. 36 pp. (http://www.portofinoamp.it/it/prodotti- Perkol-Finkel, S., Shashar, N., & Benayahu, Y. Kenchigton, R.A. 1978. Visual surveys of large fi editoriali/relazioni-tecniche/699-2004- 2006. Can arti cial reefs mimic natural reef areas of coral reefs. In: Coral reefs: research qvalutazione-e-valorizzazione-delle-emergenze- communities? The roles of structural features methods. UNESCO - Monographs on oceano- naturalistiche-dellamp-portofinoq.html). and age. Mar Environ Res. 61:121-35. http:// graphic methodology, eds. Stoddart, D.R., & dx.doi.org/10.1016/j.marenvres.2005.08.001. Cattaneo-Vietti, R., Albertelli, G., Aliani, S., Johannes, R.E., 149-62. Paris: UNESCO. Bava, S., Bavestrello, G., Benedetti-Cecchi, L., … Piazzi, L., Meinesz, A., Verlaque, M., Akçali, B., Mallefet, J., Zintzen, V., Massin, C., Norro, ć … Wurtz, M. 2010. The Ligurian Sea: Present Antoli , B., Argyrou, M., Ceccherelli, G. A., Vincx, M., DeMaersschalck, V., … Caulerpa racemosa status, problems and perspective. Chem 2005. Invasion of var. Cattrijsse, A. 2008. Belgian shipwreck: hotspots cylindracea Ecol. 26:319-40. http://dx.doi.org/10.1080/ (Caulerpales, Chlorophyta) in the for marine biodiversity (BEWREMABI). Final Mediterranean Sea: An assessment of the 02757541003689845. fi Scienti c Report. Brussels: Belgian Science spread. Cryptogam Algol. 26(2):189-202. Cerrano, C., Bavestrello, G., Bianchi, C.N., Policy. 153 pp. Cattaneo-Vietti, R., Bava, S., Morganti, C., … Relini, G. 2004. Mediterranean marine ben- Massin, C.L., Norro, A., & Mallefet, J. 2002. Sponga, F. 2000. A catastrophic mass-mortality thos: a manual of methods for its study and Biodiversity of a wreck from the Belgian episode of gorgonians and other organisms sampling. Biol Mar Medit. 10(1):267-307. continental shelf: monitoring using scientific in the Ligurian Sea. Ecol Lett. 3:284-93. diving. Preliminary results. Biologie. 72:67-72. Relini, G., Relini, M., Palandri, G., Merello, http://dx.doi.org/10.1046/j.1461-0248.2000. S., & Beccornia, E. 2007. History, ecology 00152.x. Mirto, G., Pivetta, S., & Spazzapari, G. 2009. and trends for artificial reefs of the Ligurian Relitti e navi sommerse. Liguria e Toscana. Church, R., Warren, D., Cullimore, R., sea, Italy. Hydrobiologia. 580:193-217. Milano: Magenes Editoriale srl. 510 pp. Johnston, L., Schroeder, W., Patterson, W., … http://dx.doi.org/10.1007/s10750-006-0453-0. Moore, J. 2007. Archaeological and Biological Parravicini, V., Morri, C., Ciribilli, G., Svane, I., & Petersen, J.K. 2001. On the prob- Analysis of World War II Shipwrecks in the Montefalcone, M., Albertelli, G., & Bianchi, lems of epibioses, fouling and artificial reefs, Gulf of Mexico: Artificial Reef Effect in Deep C.N. 2009. Size matters more than method: a review. PSZN I: Mar Ecol. 22(3):169-88. Water. U.S. Dept. of the Interior, Minerals Visual quadrats vs photography in measuring Management Service, Gulf of Mexico OCS human impact on Mediterranean rocky reef Tilburg, H.V. 2006. Japanese Midget Sub at Region, New Orleans: LA. OCS Study MMS communities. Est Coast Shelf Sci. 81:359-67. Pearl Harbor: Collaborative Maritime Heri- 2007-015. 387 pp. http://dx.doi.org/10.1007/s10750-006-0450-3. tage Preservation. In: Heritage at risk. Special
126 Marine Technology Society Journal edition. Underwater cultural heritage at risk: Managing natural and human impacts, eds. Grenier, R., Nutley, D., & Cochran, I., 67-9. Munchen: ICOMOS - International Council on Monuments and Sites.
Underwood, C. 2009. Public archaeology. In: Shared heritage: Joint responsibilities in the management of British warships wrecks overseas, ed. Gallagher, S., 93-109. Worverhampton: University of Worverhampton International seminar.
UNESCO. 2001. Underwater cultural heritage. Text of the 2001 Convention. Paris: UNESCO. http://ww.unesco.org/new/en/unesco/ themes/underwater-cultural-heritage/the-2001- convention/official-text/.
Walker, S.J., Schlacher, T.A., & Schlacher- Hoenlinger, M.A. 2007. Spatial heterogeneity of epibenthos on artificial reefs: fouling com- munities in the early stages of colonization on an East Australian shipwreck. Mar Ecol. 28:435-45.
Weinberg, S. 1978. The minimal area prob- lem in invertebrate communities and the abiotic environment. Mar Biol. 49:41-57. http://dx.doi.org/10.1007/BF00390728.
Wessex Archaeology Limited. 2008. Aggre- gate levy sustainability fund marine aggregates and the historic environment. Wrecks ecology 2007–08. Report Ref: 57456.02. Salisbury: Wessex Archaeology. 117 pp.
Work, T.M., Aeby, G.S., & Maragos, J.E. 2008. Phase shift from a coral to a corallimorph- dominated reef associated with a shipwreck on Palmyra Atoll. PLoS ONE. 3(8):e2989. http:// dx.doi.org/10.1371/journal.pone.0002989.
Zintzen, V., Norro, A., Massinand, C., & Mallefet, J. 2008. Spatial variability of epifaunal communities from artificial habitat: Shipwrecks in the Southern Bight of the North Sea. Est Coast Shelf. 76:327-44. http://dx.doi.org/ 10.1016/j.ecss.2007.07.012.
May/June 2013 Volume 47 Number 3 127 UPCOMING MTS JOURNAL ISSUES CALL FOR PAPERS
July/August 2013 The MTS Journal Marine Renewable Energy Technologies: Outstanding includes technical Papers from the 4th Annual Marine Renewable Energy Technical Conference papers, notes and Guest editors: Kenneth Baldwin, Stephan Grilli, Brian Howes, Daniel MacDonald, and Maggie L. Merrill commentaries September/October 2013 The State of Technology in 2013 of general interest in Guest editor: Donna Kocak November/December 2013 most issues. Technologies and Techniques for 21st Century Wet Diving Contact Managing Editor Guest editor: Michael Lombardi Amy Morgante January/February 2014 ([email protected]) Marine Technology Developments in Asia Guest editors: Dhugal Lindsay and Hiroyuki Nakahara. if you have material you Manuscripts due end of August 2013. would like considered.
Specifications for
submitting a manuscript
are on the MTS website
under the Publications menu.
www.mtsociety.org
E-mail: [email protected] Or visit our homepage at
Check the Society website for future Journal topics. www.mtsociety.org www.mtsociety.org Marine Technology Society Member Organizations
CORPORATE MEMBERS Seanic Ocean Systems QPS ABCO Subsea Houston, Texas Portsmouth, New Hampshire Houston, Texas Siemens Energy, Inc. Quest Offshore Resources AMETEK Sea Connect Products, Inc. Houston, Texas Sugar Land, Texas Westerly, Rhode Island SonTek/YSI, Inc. Remote Ocean Systems, Inc. Bluefin Robotics San Diego, California San Diego, California Quincy, MA South Bay Cable Corp. RRC Robotica Submarina C & C Technologies, Inc. Idyllwild, California Macaé, Brazil Lafayette, Louisiana Stress Engineering Services, Inc. SeaBotix CDL, Inc. Houston, Texas San Diego, California Houston, Texas Subsea 7 (US), LLC SeaLandAire Technologies, Inc. C-MAR Group Houston, Texas Jackson, Mississippi Houston, Texas Technip SEATECHRIM Compass Publications, Inc. Houston, Texas Moscow, Russia Arlington, Virginia Teledyne Benthos SeaView Systems, Inc. DOF Subsea USA North Falmouth, Massachusetts Dexter, Michigan Houston, Texas Teledyne Oil & Gas Sonardyne, Inc. Dynacon, Inc. Daytona Beach, Florida Houston, Texas Bryan, Texas Teledyne RD Instruments, Inc. SIMCorp Marine Environmental, Inc. EMAS AMC Poway, California St. Stephens, Canada Houston, Texas UniversalPegasus International, Inc. Sound Ocean Systems, Inc. Fluor Offshore Solutions Houston, Texas Redmond, Washington Sugar Land, Texas Wachs Subsea LLC Stress Subsea, Inc. Forum Energy Technologies Houston, Texas Houston, Texas Houston, Texas SURF Subsea, Inc. Fugro Atlantic BUSINESS MEMBERS Magnolia, Texas Norfolk, Virginia Aanderaa Data Instruments, Inc. Technip – Global Industries Fugro Chance, Inc. Attleboro, Massachusetts Houston, Texas Lafayette, Louisiana Ashtead Technology, Inc. Technology Systems Corporation Fugro Geoservices, Inc. Houston, Texas Palm City, Florida Houston, Texas Baker Marine Solutions Teledyne Impulse Fugro-McClelland Marine Geosciences Mandeville, Louisiana San Diego, California Houston, Texas Bastion Technologies, Inc. Tension Member Technolo gy Fugro Pelagos, Inc. Houston, Texas Huntington Beach, California San Diego, California BioSonics, Inc. VideoRay, LLC Geospace Offshore Cables Seattle, Washington Phoenixville, Pennsylvania Houston, Texas Braemar Technical Services, Inc. (Engineering) W2S2, LLC GE Energy Power Conversion Houston, Texas Houston, Texas Houston, Texas C.A. Richards and Associates, Inc. WET Labs, Inc. GL Noble Denton Houston, Texas Philomath, Oregon Houston, Texas Cochrane Technologies, Inc. WFS Technologies Ltd HARRIS CapRock Communications Lafayette, Louisiana Livingston, United Kingdom Melbourne, Florida Contros Systems & Solutions GmbH Xodus Group Hydroid, LLC Kiel, Germany Houston, Texas Pocasset, Massachusetts DeepSea Power and Light Innerspace Corporation San Diego, California INSTITUTIONAL MEMBERS Covina, California Deepwater Rental and Sypply Associacio Institut Ictineu Centre, Catala De Recerca INTECSEA New Iberia, Louisiana Submarina Houston, Texas DPS Offshore Inc. Barcelona, Spain InterMoor, Inc. Houston, Texas Canadian Coast Guard Houston, Texas Embient GmbH St. John’s, Newfoundland and Labrador, Canada J P Kenny, Inc. Halstenbek, Germany City of St. John’s Houston, Texas Energy Sales, Inc. Newfoundland and Labrador, Canada Kongsberg Maritime, Inc. Redmond, Washington CLS America, Inc. Houston, Texas Falmat, Inc. Largo, Maryland L-3 Communications San Marcos, California Consortium for Ocean Leadership Houston, Texas FASTORQ Washington, DC L-3 MariPro New Caney, Texas Department of Innovation, Trade and Rural Goleta, California Fugro Atlantic Development Lockheed Martin Sippican Norfolk, Virginia St. John’s, Newfoundland and Labrador, Canada Marion, Massachusetts Fugro GeoSurveys, Inc., a division of Fugro Fundação Homem do Mar MacArtney, Inc. Canada Corp. Rio de Janeiro, Brazil Houston, Texas St. John’s, Newfoundland and Labrador, Canada Harbor Branch Oceanographic Institute Marine Cybernetics AS GAC Shipping (USA) Inc. Fort Pierce, Florida Trondheim, Norway Houston, TX International Seabed Authority Mitsui Engineering and Shipbuilding Co. Ltd. Horizon Marine, Inc. Kingston, Jamaica Tokyo, Japan Marion, Massachusetts Jeju Sea Grant Center Oceaneering Advanced Technologies HortonGMC Jeju-City, South Korea Hanover, Maryland Houston, Texas Marine Institute Oceaneering International, Inc. Huisman North America Services Newfoundland and Labrador, Canada Houston, Texas Rosenberg, Texas Monterey Bay Aquarium Research Institute OceanWorks International ISR Group Moss Landing, California Houston, Texas Savannah, Tennessee National Research Council Institute for Ocean Technology Odyssey Marine Exploration iXBlue, Inc. St. John’s, Newfoundland and Labrador, Canada Tampa, Florida Cambridge, Massachusetts Naval Facilities Engineering Service Center Oil States Industries, Inc. Knight, LLC Port Hueneme, California Arlington, Texas Lake Forest, California NAVFAC Atlantic OceanWorks International International Submarine Engineering, Ltd Norfolk, VA Houston, Texas Port Coquitlam, Britsh Columbia, Canada NewcastleGateshead Initiative Petrustech Oil & Gas Liquid Robotics, Inc. Gateshead, United Kingdom Houston, Texas Palo Alto, California Noblis Phoenix International Holdings, Inc. London Offshore Consultants, Inc. Falls Church, Virginia Largo, Maryland Houston, Texas OceanGate, LLC Pratt & Whitney Rocketdyne Inc. Makai Ocean Engineering, Inc. Miami, Florida Beverly, MA Kailua, Hawaii Oregon State University College of Oceanic and QinetiQ North America – Technology Solutions Group Maritime Assurance & Consulting Ltd. Atmospheric Sciences Slidel, Louisiana Aberdeen, United Kingdom Corvalis, Oregon Raytheon Technical Service Company, LLC Matthews-Daniel Company Richard Stockton College of New Jersey Saipem America, Inc. Houston, Texas Port Republic, New Jersey Houston, Texas Oceanic Imaging Consultants, Inc. Schmidt Ocean Institute SBM Atlantia Honolulu, Hawaii Lake Forest Park, Washington Houston, Texas Offshore Inspection Group, Inc. U.S. Naval Academy Library Schilling Robotics, LLC Houston, TX Annapolis, Maryland Davis, California Poseidon Offshore Mining University of Massachusetts–Dartmouth SEA CON Brantner and Associates, Inc. Oslo, Norway New Bedford, Massachusetts El Cajon, California
The Marine Technology Society gratefully acknowledges the critical support of the Corporate, Business, and Institutional members listed. Member organizations have aided the Society substantially in attaining its objectives since its inception in 1963. Postage for periodicals is paid at Washington, DC 1100 H Street NW, Suite LL-100 and additional mailing offices. Washington, DC 20005