Study On Longitudinal Motion Suppression And Size And Layout Of Appendages For High Speed Trimaran

High speed trimaran has excellent rapidity and lateral seakeeping,and has a good bearing capacity.It is widely used in military and civil fields.However,when the sea conditions are bad the problem of excessive longitudinal motion will occur,which will cause discomfort to the crew and damage to the equipment.The purpose of this thesis is to suppress the heave and pitch of high-speed trimaran by controlling the angle of attack of T-foil and Flap,and further enhance their control effect on the basis of passively suppressing the longitudinal motion of high-speed trimaran by using the damping performance of appendages.Firstly,the mathematical model of longitudinal motion of high-speed trimaran is established.The parameters such as added mass and added damping coefficient of the model are calculated by using hydrodynamic software.The force to longitudinal motion model is established.The ratio and phase of longitudinal motion and wave height of high-speed trimaran under different encounter frequencies are used to fit the disturbance of wave to high-speed trimaran.Based on the wave spectrum theory,the wave model is established,and considering the wave disturbing force model,the disturbing force model of different sea conditions is established.The lift coefficient of appendage is obtained by simulation,and the mathematical model is established according to the relationship between lift and angle of attack.Secondly,the stability of the system ensures the rationality of the ship’s longitudinal motion model,the controllability and observability of the system ensure the feasibility of the comprehensive design of the system,and the dynamic performance of the system is analyzed.The influence of pitch and longitudinal velocity of hull on appendages is analyzed,and the change of longitudinal motion of ship considering these factors is simulated.The principle of restraining longitudinal motion of fixed appendages is clarified.Then,the decoupling PD controller is designed to decouple the angle of attack,heave and pitch of the T-foil and Flap,and the PD controller is used to control the decoupled system.Considering the uncertainty of the actual navigation of the ship,the H_∞control developed from the robust control is designed,and the specific control parameters of the H_∞controller are obtained by using the linear matrix inequality method It can be seen that the control effect is better when uncertain model appears.Finally,the control effect of H_∞controller designed by the same design method is compared when the size and layout of appendages are changed,and a better group of appendages is selected to maximize the longitudinal motion suppression ability of the control system.At the end of this study,a controller is designed,which can greatly reduce the longitudinal motion caused by ocean waves,so that the anti-disturbance ability of the longitudinal motion system of high-speed trimaran is improved,and the control effect is verified by simulation.it lays a foundation for the follow-up theoretical research.