The potential energy savings by application of a wave foil on the autonomous container vessel ReVolt Eivind Finne Riley Marine Technology Submission date: June 2015 Supervisor: Sverre Steen, IMT Co-supervisor: Eirik Bøckmann, IMT Norwegian University of Science and Technology Department of Marine Technology MASTER THESIS IN MARINE TECHNOLOGY SPRING 2015 FOR EIVIND FINNE RILEY The potential energy savings by application of a wave foil on the autonomous container vessel ReVolt An ongoing research project in DNV GL Research is the autonomous, electrically propelled container ship concept ReVolt; a container vessel designed to operate in the Norwegian coastal seas between Oslo and Trondheim. The ship is designed to sail at slow forward speeds, minimizing the energy needed for propulsion. The preliminary calculations show that the needed power output for sailing at 6knots in calm seas is merely 50kW. However, in sea states with waves, the power needed to sail in the desired speed of 6 knots increases significantly, and added resistance in waves becomes the largest resistance component of the vessel. In order to always being able to return safely to harbor, ReVolt has to be equipped with a battery pack with sufficient energy stored to safely return the ship to harbor at a worst case weather scenario. This master project will look into the use of a wave foil to reduce the ReVolt ships resistance when operating in waves, in order to reduce the size of the required battery pack, and also to reduce the power consumption in general. The objective of the master project is therefore to design an optimized wave foil system aiming to minimize the required battery capacity on the ReVolt ship. To reach the objective, the following steps are recommended: Design a wave foil system for ReVolt. The foils must be retractable to avoid resistance increase in calm water. A detailed study of the mechanisms for retraction is out of scope, but indications of how it can be achieved should be given. It is likely that an iterative approach must be taken to reach a foil system design which is as close to optimal as possible. Establish methods for evaluation of the net thrust produced by the foil system(s) in different wave conditions. It is foreseen that this part can be based on existing methods, but a selection of method has to be performed, and the choices made should be argued for. It is recommended to somehow include the effect of stall on the foil lift and drag. It is also recommended to check the benefit of pitch control, either active (by use of an active control system) or passive (feathering). It can be assumed that the ship will stay in harbor when the operating conditions are such that important operational criteria might be exceeded. Such criteria might be of different types. Examples are: sufficient battery capacity, safety and stability of vessel, cargo safety criteria related to accelerations and/or maximum inclination angles. It is recommended to establish a set of operational criteria, and use them to assess under which conditions the ship should leave port. It might be of interest to see how the operability of the ship changes when it is equipped with foils. Evaluate the foil thrust and resulting required propeller power in the critical routes under all expected weather conditions. Compare the required total energy for the case of no foils, with fixed foils, and with controlled foils (could be spring loaded). It should be kept in mind that for the alternatives with foils the conditions with the largest waves might not require the most energy, due to the effect of the wave foils. It is recommended to relax the requirement for keeping a speed of six knots. Give recommendations for further work, and for what is considered the best option for ReVolt with respect to use of foils. - 1 - In the thesis the candidate shall present his personal contribution to the resolution of problem within the scope of the thesis work. Theories and conclusions shall be based on mathematical derivations and/or logic reasoning identifying the various steps in the deduction. The thesis work shall be based on the current state of knowledge in the field of study. The current state of knowledge shall be established through a thorough literature study, the results of this study shall be written into the thesis. The candidate should utilize the existing possibilities for obtaining relevant literature. The thesis should be organized in a rational manner to give a clear exposition of results, assessments, and conclusions. The text should be brief and to the point, with a clear language. Telegraphic language should be avoided. The thesis shall contain the following elements: A text defining the scope, preface, list of contents, summary, main body of thesis, conclusions with recommendations for further work, list of symbols and acronyms, reference and (optional) appendices. All figures, tables and equations shall be numerated. The supervisor may require that the candidate, in an early stage of the work, present a written plan for the completion of the work. The plan should include a budget for the use of computer and laboratory resources that will be charged to the department. Overruns shall be reported to the supervisor. The original contribution of the candidate and material taken from other sources shall be clearly defined. Work from other sources shall be properly referenced using an acknowledged referencing system. The thesis shall be submitted electronically (pdf) in DAIM: - Signed by the candidate - The text defining the scope (signed by the supervisor) included - Computer code, input files, videos and other electronic appendages can be uploaded in a zip-file in DAIM. Any electronic appendages shall be listed in the main thesis. The candidate will receive a printed copy of the thesis. Supervisor : Professor Sverre Steen Advisor : Eirik Bøckmann Start : 15.01.2015 Deadline : 10.06.2015 Trondheim, 15.01.2015 Sverre Steen Supervisor - 2 - Preface This report is my MSc. Thesis in marine hydrodynamics written at the Dpt. Of Marine Technology at the Norwegian Institute of Technology and Science (NTNU) in Trondheim, Norway. The project was written in the spring of 2015. The motivation behind the thesis is to determine whether an application of propulsion foils could reduce the dimensioning battery size of the autonomous, electrically driven concept container ship ReVolt. The idea arose after seeing a presentation of ReVolt at a summer internship at DNV GL at Høvik. I had vaguely heard about propulsion foils before attending the presentation, and after hearing that ReVolts major contributor to the battery pack size was the added resistance imposed in waves. I suggested doing an analysis of this in my master thesis in hydrodynamics, and caught DNV GLs interest in the subject. Many people deserve thanks for the completion of this project. I would like to thank my supervisor Sverre Steen for accepting the thesis, and for his guidance during the work. PhD candidate Eirik Bøckmann at NTNU also deserves many thanks for his help. Lars Øien and Dariusz Fathi at MARINTEK has also helped with use of computer programs used in this thesis. I would also like to thank Hans-Anton Tvete, Christos Chryssakis and Bjørn-Johan Vartdal at DNV GL Høvik for taking interest in the subject and for their help, in addition to Bingjie Guo and Stian Bakke Tornes. My friends and fellow office-dwellers at NTNU Tyholt deserve great thanks for their continuing help and friendship. Especially Rasmus Borenius has been an important friend and working companion throughout my years in Trondheim. Finally, I would like to thank my parents, Elisabeth and Hugh. Their support and love seems never-ending, and I would not be where I am today without you. Trondheim, June 10th 2015 Eivind Finne Riley i Summary ReVolt is an electrically propelled, autonomous concept container ship designed by DNV GL to minimize the energy consumption and cost; however, the added resistance in waves is a large resistance contributor. Effectively, this means that the battery packs of ReVolt have to be dimensioned sufficiently large to be able to complete its route legs in the worst sea states ReVolt might encounter. Batteries of today associated with a high cost. The main focus in this thesis is assessing the benefits in terms of capital expenses (CAPEX) for ReVolt achievable by fitting so-called wave foils at the bow of the vessel. Continuous operational expenses (OPEX) is also assessed to a lesser extent. A considerable amount of previous work has been done on the topic of wave foils in the past by other authors, and an overview of previous theoretical work and model- and full scale trials is presented. As far as known by the author, this is the first time wave foils have been tried as a CAPEX savings device in relation to electrical, sea going vessels – earlier work on fuel savings have been performed more in relation to general OPEX savings. To examine the foil performance in irregular sea, a large amount of irregular sea states are simulated, and the time averaged foil performance is found through a frequency-domain analysis. Linear foil theory is applied; however, a stalling model is implemented to model the potentially important stalling effects on the foil, which is not included in regular foil theory. The model also includes the effect of unsteady lift on an oscillating foil, and additional resistance components imposed by the foil system. The thrust production and motion dampening effect reduces the total ship resistance in sea states applicable for wave foils. Further, the needed brake power in the examined sea states is calculated. The brake power is then converted to total energy consumption by defining a dimensioning sailing distance.