An Investigation Of Numerical Prediction Model For Ship Large Amplitude Motion Based On GN Wave Theory

As shipping business of China moves from offshore to distant seas,the explosive marine environment poses new challenges to the dynamic stability of ships.It is necessary to conduct numerical prediction research on the large amplitude nonlinear motion of ships in severe sea conditions.The incident waves are the primary environmental loads encountered by ships when they sail at sea.The accurate simulation of the wave environment is the basis for ship hydrodynamic analysis and motion prediction.A fully nonlinear wave theory which called GN wave theory is introduced.Based on the wave theory,a weakly nonlinear numerical calculation model is established for ship's three-degree-of-freedom heave-roll-pitch coupling motion,in which the incident wave force and hydrostatic recovery force are calculated on the instantaneous wet surface below the water surface.The radiation force and the diffraction force are calculated by the linear method using the impulse response function,and the floating slamming force load is introduced according to the momentum theorem.The wave field of the GN wave model is confirmed,and simultaneously analyzes the irregular waves generated by the GN wave theory and the linear wave theory,and studies the difference between the two wave theories.Second,the motion model based on GN wave is used to simulate the heave and pitch motion of S175 container ship with higher forward speed in regular and irregular waves,and the results are compared with the results of the model tests.Finally,the parametric rolling of the C11 container ships was studyed in regular waves and irregular waves.Experimental date shows that the wave elevation of irregular waves in high sea conditions is nonlinear,and the probability distribution of the peak-to-trough value deviates om the Rayleigh distribution,the peak value is greater than the trough value.Through the statistical analysis of the numerical simulation results of irregular waves,it is proved that GN wave theory shows the same phenomenon with experimental results.It is proved that the motion simulation results of S175 container ship are in good agreement with the test results,and the forecast results are larger than the results based on linear wave theory.It is proved that the established mathematical model is suitable for simulating ship's parametric rolling.The steady parametric rolling amplitude of the numerical simulation based on GN wave theory is not much different om the model test in regular waves.If there is a large number of rolling time history,a stable roll significance amplitude confidence interval can be obtained,which can represent the ship's roll motion in irregular waves.