Modeling Of Ship Sea-keeping Motion Based On Response Amplitude Operator

When ship is sailing on the sea,as a result of the action of wind and waves,it can produce six degrees of freedom oscillation motion,the influence of roll,pitch and heave motion of the ship on the driver is more outstanding.In order to increase the fidelity of the navigation simulator,also considering that normal sea condition the encountered by ship is irregular waves and sea condition on ordinary voyage objectively can't be head sea or following sea,at the same time in response to DET NORSKE VERITAS standard demand for mathematical model of Marine simulator and etc,in view of the above,this paper does the following research work:Firstly,establishing a linear model of ship in still water.According to the free swing decay curve of Delta Linda tugboat,under the assumption of linear damping,the decay coefficient of the simplified linear model of three degrees of freedom of ship is calculated by using the general theory of ship seakeeping,and the obtained coefficient is substituted into the free swing decay model.Secondly,deriving the expression of wave disturbing torque of ships in irregular oblique waves.Based on the stress analysis of ship in regular waves and regarding the wave described by ITTC spectrum as the research object and using linear superposition principle of the movement,the superposition of regular wave implement irregular wave.On the premise of Froude-Krylov hypothesis,considering the effect of the change of wave direction on external disturbance torque about heave and pitch motion of the ship,eventually determine the irregular wave interference torque expression.The rationality of the described wave force is proved by comparing the experimental data with the numerical data of the model under a given wind level.Thirdly,the described method of frequency domain response amplitude operator and the method of numerical solution are used to solve the motion response of ships in irregular waves.The direct time-domain method and frequency-time-domain-conversion method are used to solve the ship's swing motion by using the seakeeping separation modeling method.Fourth,basing on the Delta Linda platform,the advantages of linear frequency-domain method over time-domain method are proved.The method of frequency domain is better than that in time domain in stability for ship motion solution in marine simulator.The method of frequency domain analysis of ship swing motion has a strong theoretical basis.The solution of the model is relatively clear and The hardware requirements are not very high.Fifth,it is good to eliminate the picture jump phenomenon in visual system of ship simulator with factitious trim algorithm,which lays the foundation for the further research work.