Investigation Of Active Hydrofoil Control Strategies On Autonomous Ship

Surface autonomous ships have the characteristics of high speed,excellent stealth performance,easy mass production and convenient layout,which is very suitable for becoming a general unmanned,highly intelligent and information-based marine weapons and equipment,and high speed,high sea-keeping and high maneuverability are the basic requirements for the navigation performance of autonomous ships on the surface.In this paper,aiming at the key problem of improving the sea-keeping of autonomous ships,the study uses numerical and experimental methods to investigate the active hydrofoil control strategy of autonomous ships,and proposes a practical and effective hydrofoil control strategy.Firstly,in this paper,a numerical method for the effect of active controlled hydrofoil based on free surface discrete vortex method is constructed.The correctness of the numerical method was validated through comparing the results of the experiment.Numerical studies put forward four active control strategies,passive,linear,step and hybrid control,as well as two active control signals of pitch velocity and bow vertical velocity.The three longitudinal motion responses of the Wigley III ship model with T-foil are simulated under three active control methods at different waves and speeds.Based on the control effect percentage of simulation results,the bow vertical velocity signal performs better than the pitch velocity signal.The control results of the linear control and step control are significant when the encounter frequency is in resonance zone but not obvious when the encounter frequency deviates the zone.The hybrid control has the strengths of both linear and step control methods and can effectively control the ship longitudinal motions.The control effect of the strategy is decided by a control intensity gain,CI,which drives the method that could work more steady and handle various wave conditions.Then,to investigate the performance of the hybrid control strategy,experimental tests were conducted in a towing tank of Dalian University of Technology.In the study,a model of a high-speed trimaran with active motion control hydrofoil was built and tested in head seas with various wave lengths at two forward speeds.The control strategy used in the experimental study is as same as the strategies in the numerical study,where the hybrid control strategy is optimized and the control intensity parameter is changed from a percentage to a fixed value.In the experiment,the heave,pitch and acceleration responses of the highly trimaran model in the regular waves were monitored,and the longitudinal motion control effects of different control strategies were compared.The experimental results were consistent with the numerical results,and the hybrid control strategy had a significant motion control effect at the full encounter frequency and had better adaptability than the other two control strategies.Finally,the results of numerical research and experimental research are systematically summarized and analyzed,and it is concluded that the active control hydrofoil with the bow vertical velocity signal hybrid control strategy has the best improvement effect on the sea-keeping of autonomous ships,which provides a certain reference for the development of active hydrofoil control strategy for autonomous ships.