Research On Modeling And Simulation Of Yacht Porpoising Motion

There is a big difference between the yacht simulator and the traditional navigation simulator.The difference is mainly in the mathematical model of ship motion.The simulation objects of navigation simulators are mainly commercial ships,which are all displacement ships,and most of the yachts are high speed planing boats.There are huge differences between them in terms of motion attitudes and fluid hydrodynamics.Therefore,the research methods of ship motion in navigation simulators are not suitable for yachts.In order to improve the accuracy of yacht motion and improve the quality of yacht simulators,it is urgent to propose a new modeling method suitable for yachts.In this thesis,the porpoising motion is taken as the research direction,and the single high speed yacht is taken as the research object.The main work is as follows:Porpoising motion is a phenomenon that occurs when yachts sail in still water at high speed.Therefore,the yacht’s high-speed motion in still water is first studied.In the process of the yacht moving from static to high speed,its sailing attitude and force change greatly.The modeling and simulation of the above two kinds of changes have not been realized in the navigation simulators.To solve this problem,the yacht motion is studied based on the Savitsky theory.In order to reduce the computational complexity of the model and improve the general applicability of the algorithm,the yacht is simplified to a prism body.In the Savitsky theory,the influence of ship buoyancy is completely ignored,which leads to the problem of poor simulation accuracy of resistance and trim angle in the low-speed domain of the ship.The idea of dichotomy is used as a guide,and a piecewise modeling method is proposed to solve the problem.The hybrid method is adopted in the low-speed domain,the Savitsky method is adopted in the high-speed domain,and then the ship motion model at high-speed in still water is established.The simulation results of the method are compared with the model test.The results show that the simulation accuracy of the model is good,and it can be used in the yacht simulator.The occurrence of porpoising motion is caused by the small disturbance of the free surface when the ship is sailing at high speed,which results in the change of the hydrodynamic force of the fluid on the ship.The simulation of the rapid change of the free surface requires a lot of calculations,and the simulator cannot provide huge calculation resources and sufficient calculation time.Therefore,the hydrodynamic coefficients of heave and pitch are calculated by analytical methods based on the prismatic assumption,high frequency free surface assumption and slice theory.Routh-Hurwitz linear stability criterion is used to find the boundary conditions of porpoising motion.A small external disturbance is introduced as a result of the disturbance of the free surface,then a yacht in an unstable state of motion will have porpoising motion.The method is compared and verified with the model test.The results show that the external disturbance item will promote the occurrence of porpoising motion when and only when the yacht is in an unstable state.The disturbance item does not affect the motion of the yacht in a stable state.The model has good calculation accuracy and can be used in the simulator.In order to further enhance the theoretical depth of the research and improve the simulation accuracy,the slamming theory is used to study the lift of yachts at high speed in this paper.The extended MLM method is used to calculate the two-dimensional slamming force of the section in the transverse of the ship.The forces and the moments are summed in the direction of the ship length based on 2D+T theory.In the 6 DOF(Degree of Freedom)motion of a yacht,there is a strong correlation between heave,pitch motion and surge motion.The direct resistance of the yacht is used as the combination point,the 3 DOF maneuverability equation and the 2 DOF seakeeping equation are coupled,the rolling motion is considered separately.A 5 DOF+1 DOF mathematical model is established.The maneuverability test in still water and the test in regular waves have been carried out,and the simulation effect is good.The model in this paper is integrated with the yacht simulator,and the simulation result is good.In summary,the researches in attitude,force and stability of yachts during high-speed sailing are carried out based on the improved Savitsky method,artificial perturbation,extended MLM method,and a 6 DOF mathematical model suitable for the yacht simulator is established.On this basis,the algorithm is integrated with the yacht simulator,and the engineering application is carried out.On this basis,the algorithm is integrated with the yacht simulator,and the engineering application is carried out...