Study On The Improvement Of Ship Seakeeping And Maneuvering Performance Based On New Concept Energy Saving Propulsive Hydrofoils

Under the background of global warming due to green house gas emissions and the energycrisis due to decreasing oil resources, the ship industry is facing both substantial challenges andopportunities. Energy saving and environmental protection is going to become one of the corecompetitiveness in the ship market.In this study, a new concept energy saving technology for assisting ship propulsion and pathfollowing is proposed based on the so called T-shaped Wave Devouring Hydrofoil (T-WDH) tech-nology. The horizontal part of the T-WDH can recover wave energy through ship motions andproduce thrust to assist propulsion. Moreover, it can act as motion stabilizers to reduce the shipmotion responses in waves. The vertical part of the T-WDH is used as bow rudders to improvethe maneuverability of the ship. The hydrodynamic performance of the T-WDH is studied throughtheoretical modeling and experimental analysis; the performance of T-WDH at actual seas is alsopredicted. On the other hand, a4DoF nonlinear maneuvering model is established to simulateand analyze the T-WDH ship maneuvering performance in calm water and in waves. To achievethe coordinated path following control between the T-WDH and the aft rudder, a controller basedon offset-free model predictive control is developed; the online parameter identification scheme isalso adopted to enhance the robustness of the controller.This thesis is divided into seven chapters:In Chapter1, the author introduces of the background and the significance of this study, andsummarizes the state of art of ship energy saving technologies in the world to propose the T-WDHship energy saving technology concept and discusses the key points for further studies.In Chapter2, a ship seakeeping prediction method based on Method of Fundamental Solutions(MFS) is introduced to lay the foundation for subsequent T-WDH ship seakeeping study. The math-ematical principle of MFS is elaborated in detail, then the numerical modeling and computationanalysis are carried out for the prediction of2D sectional hydrodynamic coefficients based on po-tential flow. The MFS method is compared with Boundary Element Method (BEM) to demonstrateits desingularized, boundary exact and derivative continuous features. Moreover, MFS method is mathematically simple and easy for programming. MFS method is then integrated into the striptheory to predict the seakeeping performance of a containership and a tanker, showing its feasibilityfor actual hull forms.In Chapter3, the author reviews the state of art of relevant studies on wave devouring hy-drofoils, and establishes the coupled hydrodynamic model between T-WDH and the ship basedon frequency domain potential theory, which can predict the heave and pitch responses in regularhead waves. The wave added resistance evaluation method in the presence of T-WDH is then s-tudied. To validate the model, the S175containership is adopted for T-WDH design and towingtank seakeeping experiment. Comparison between the numerical and experimental results provethe correctness of the model and the practicability of this technology.In Chapter4, the influence of T-WDH design parameters and connection method on shipseakeeping performance is investigated; then, the short-term prediction method of ship seakeepingperformance and the speed loss coefficient based on hull-engine-propeller matching are introduced.Long-term prediction model of performance at actual seas is then elaborated, including the intro-duction of the Wind and Wave Database and the long-term prediction method. Finally, a3100TEUcontainership is adopted for short-term and long-term performance prediction along her route.In Chapter5, the4DoF nonlinear maneuvering model for S175containership is establishedwith the elaboration of the modeling for hull forces, propeller forces, rudder forces and wavedrift forces in detail. Validation is performed to demonstrate the correctness of this simulationplatform. The bow rudder part of the T-WDH is then designed. Finally, comparative study on themaneuvering performance is carried out between the T-WDH ship and the original ship.In Chapter6, the coordinated path following control between T-WDH and the aft rudderbased on model predictive control is studied. To deal with the wave disturbances, the offset-freemodel predictive control scheme is proposed to reduce the steady state path following error; thecontroller is tuned in the nonlinear maneuvering simulation test bed. Then, the online adaptiveparameter identification scheme is studied to take advantage of the unique feature of using bothbow and aft rudders. The feasibility and practicability of the scheme is proved through simulationin the test bed.Chapter7includes the main conclusions of the thesis and some suggestions for future studies.It can be concluded that the proposed new concept energy saving propulsive hydrofoil caneffectively improve the ship seakeeping and maneuvering performance. Model experiment resultsshow that the heave and pitch responses can be significantly reduced, with the peak response beingreduced by more than25%; the responses of wave added resistance are reduced even more, witha peak response reduction of80%. The ship speed loss coefficient prediction results at actual seasalso demonstrate the beneficial effect of this technology in raising ship energy efficiency and reducethe EEDI value. On the other hand, the bow rudder that comes with the hydrofoil can improve the ship maneuvering performance through reducing the turning diameters of the ship both in calm andin wave fields. The average reduction can reach15%. An adaptive path following controller for thebow-aft rudder combination is designed to achieve the automatic controller update when the shipchanges her speed, which again demonstrates the unique advantage of applying this technology.There are also some innovations on the theoretical level. MFS method is applied for the firsttime to the ship seakeeping prediction field and a practical numerical method for the computationof the hydrodynamic coefficients of a2D section in finite water depth is proposed; a speed loss co-efficient prediction method based on hull-engine-propeller matching is proposed to take the energytransfer process into account; the innovative concept of ship maneuvering with both bow and aftrudders is studied, and an offset-free path following control algorithm based on model predictivecontrol is proposed to reduce the steady state path following errors in wave fields.This study expands the technical storage of ship energy saving technologies, and offers somereference for the development of new generation low energy consumption, low emission and lowcarbon footprint ships.