Submarine Taniwha - Design Report New Zealand's fin driven, human powered submarine 2015 Prepared by: Ben Pocock, Gerrit Becker, Christopher Walker, Sanjay Surendran, Alex Cashen, Jonathan Chaplow, Andreas Tairych, Iain Anderson Contents 1 Scope 1 2 Introduction 1 3 Background 2 3.1 Inspiration . 2 3.2 History . 3 3.3 Design Philosophy . 3 3.4 Knowledge Retention . 4 4 Submarine Systems 4 4.1 Overview . 4 4.2 Hydrodynamics . 6 4.3 Hull and Chasis . 8 4.4 Nose cone . 9 4.5 Control Surfaces . 10 4.6 Control Mechanisms . 13 4.6.1 Elevator Hydraulic System . 13 4.6.2 Rudder Hydraulic System . 14 4.6.3 Feedback Mechanisms (Detent) . 14 4.7 Buoyancy Control . 16 4.7.1 Electric Pump System . 16 4.8 Propulsion . 17 4.8.1 Fin Design . 17 4.8.2 Pedals . 19 4.9 Pilot . 19 4.9.1 Egress . 19 4.9.2 Ergonomics . 20 4.9.3 Air Supply . 21 4.10 Safety . 22 4.10.1 Emergency Pop-Up Buoy . 22 4.10.2 External Facing Pressure Gauge . 24 4.10.3 Hatch Attachment . 24 4.10.4 Strobes . 25 4.10.5 High Visibility Mohawk . 26 4.10.6 Foot Restraints . 26 4.11 Electronics . 26 4.12 Trolley . 27 5 Preparation and Procedures 28 5.1 Testing . 28 5.2 Team . 29 6 Conclusion 30 7 Future Work 30 7.1 Automated Ballast System . 30 7.2 Novel Drag Reduction . 30 8 Appendix 31 8.1 Taniwha Photos . 31 8.2 CFDImages . 33 Taniwha Design Report 2 INTRODUCTION 1 Scope This document outlines the design and development plan for the human powered submarine Taniwha. It also provides information on the team's motivation to compete in the International Submarine Races and some of the non-technical challenges associated with the project. 2 Introduction The submarine Taniwha is a single person, human powered, wet submarine. It was built in the Biomimetics Laboratory of the University of Auckland and has the privilege of being the only Southern Hemisphere competitor in the ISR. The team consists of undergraduate and PhD students, post-doctoral researchers and academics from around the university. The project started as part of a wider goal to advance the field of underwater human movement and first competed at the European International Submarine Race (eISR) in 2014. Thrust is provided by pedal driven fins mounted to the top and bottom of the submarine, inspired by the Leatherjacket fish (Parika Scaber). Innovations in Taniwha includes the following advances and features: 1. A very thin (approximately 2.5 mm) hull - With such a thin hull the entire submarine (minus scuba bottles) can be carried by 2 people. 2. Screw attachment of the two part hull - The screw attachment allows quick and easy hull removal for access to the internal chassis. With this feature all major submarine systems can be easily altered or upgraded. 3. Adjustable ballast trim - A motorized constant volume ballast adjustment system can move up to 2 kg of water fore or aft; a useful feature for fine trimming and for diving the sub downwards or steering its nose upwards from the bottom. 4. A coupled double Hobie Mirage fin drive - The pilot, with one pair of feet can operate two fin sets that are coupled to work synchronously. 5. Hydraulics - Dive planes, rudder and safety buoy are controlled using hydraulic actuators. 6. A push-out nose cone - This added safety feature allows the pilot emergency escape through the front of the submarine. The nose cone, attached to the hull front using magnets with locator pins, can be pushed off from the inside. 1 Taniwha Design Report 3 BACKGROUND 3 Background 3.1 Inspiration Although we can stay underwater with an aqualung for about an hour or so we are greatly impeded by our low speed and lack of manoeuvrability. A diver's top speed is about 1 m/s [1], quite slow when in tidal currents that can exceed 3 m/s and very slow compared with marine mammals such as the Bottlenose dolphin that can swim up to 6 m/s [2]. We are held back by limited muscle-power, a land-based physiology and the high drag that our bodies and equip- ment create. Our dream is to produce a human-powered submersible that will augment our ability to swim and overcome these issues. Our human-powered submarine Taniwha represents our first “fin-kick" in this direction. Taniwha is driven by fins, like its Polynesian namesake, a mythical malevolent water spirit in the shape of a large fish. Fish use their fins for several functions: clearly they provide propulsion but can also be folded back for gliding, and used for steering and braking. They impart great manoeuvrability en- abling navigation in close proximity to rocks and weed. There is no need for a gearbox; the action is direct from the limb to the fin. If we were like fish we would be able to move around effortlessly, feeling and responding to minute pressure changes in water [3] and sending it back- ward in an efficient way. Propellers are also efficient but it would be virtually impossible to match the manoeuvrability of fish and the multi-functionality of the fin with a propeller driven craft. It would also be impossible to feel the water through a gearbox. The successful deploy- ment of a fin driven sub is clearly a far-reaching goal and we are no where near doing this yet. We are starting our exploration using our submarine. Taniwha's fin configuration is inspired by the NZ Leatherjacket (Parika scaber): a triggerfish that uses wave-like ripples along dorsal and anal fins to create thrust for manoeuvring and for- ward swimming. They steer with a tail that acts like a rudder (Fig. 1). We have not attempted to mimic the wave-like ripple of the Leatherjacket but we have arranged human powered fin propulsors in corresponding positions on the top and bottom surfaces. 2 Taniwha Design Report 3 BACKGROUND Figure 1: A young New Zealand Leatherjacket (Parika scaber). Swimming thrust is developed from wave-like movement of the dorsal and anal fins with the tail acting like a rudder. (Photo: I. Anderson) 3.2 History Work on Taniwha 1.0 started in mid-July 2013 in preparation for the 2nd European Interna- tional Submarine Races to be held in Gosport UK, July 2014. The hull design evolved from the geometry of a 3 m long streamlined solid of revolution model that was tested in the David Taylor Model Basin at Carderock Maryland [4]. The design philosophy of Taniwha 1.0 was to maximise manoeuvrability by having large control surfaces. The elevators were positioned for- ward of the centre of gravity to mimic pectoral fins. This did provide excellent manoeuvrability but caused a positive feedback loop and instability at higher speeds. The ensuing collisions also caused breakage of some key components making the submarine more difficult to control. Despite this, Taniwha was awarded the eISR trophy for "Best Non-propeller Performance". 3.3 Design Philosophy From the experience gained at eISR a new design philosophy has been developed. For the 2015 preparations reliability and simplicity have been encouraged. Reliability is achieved by designing failure modes, building fail-safes and frequent testing. Design decisions were mostly 3 Taniwha Design Report 4 SUBMARINE SYSTEMS based on qualitative analysis and empirical data rather than stringent quantitative design. Quantitative analysis has its place and was used where appropriate. This combination allowed for rapid innovation and ensured the development was in-line with the actual goals. An example of the design philosophy is the rudder; CFD and other quantitative methods were used to find the most efficient shape for the rudder. A larger rudder gives more turning force, but the magnitude of force actually required was unknown. Therefore the correct size of the rudder, required to sufficiently change the submarine's trajectory, had to be determined empirically through testing. 3.4 Knowledge Retention The first step in preparing for ISR 2015 was to ensure that all of the knowledge gained and lessons learned from building Taniwha 1.0 were retained. The nature of a university based project is to have a high turnover of people. If not properly managed this can easily result in a loss of knowledge from year to year. In an effort to combat this, several protocols have been created. The submarine team is part of a wider society of students and staff with interests in underwater engineering; this broadens our shared knowledge base. Each system that is developed is documented with special sections for lessons learned and results from tests of designs that did not make it into the final product; this limits duplicated effort. At the beginning of each development cycle new team members are introduced to past members and a proper hand over takes place. 4 Submarine Systems 4.1 Overview The submarine has been designed for rapid development and as such is inherently modular. Most of the sub-systems attach to chassis which is able to be completely removed from the hull. 4 Taniwha Design Report 4 SUBMARINE SYSTEMS Figure 2: a: Nose cone, b: Chassis, c: Control Handles d: Main Air Supply, e: Hull, f: Front Ballast Tanks, g: Main Hatch, h: Drive Mechanism, i: Safety Buoy and Safety Boy Release, j: Rear Ballast Tanks, k: Rudder, l: Elevators and Stabilisers. 5 Taniwha Design Report 4 SUBMARINE SYSTEMS 4.2 Hydrodynamics The hydrodynamic forces are created by the relative movement of the submarine and the fluid it operates in. Detailed explanations of the principles of hydrodynamics are beyond the scope of this report but it is important to discuss the main points that guided the development process.