Simulation And Analysis Of Ship Parametric Excitation Roll In Random Wave Group

Parametric excitation roll phenomenon refers to the nonlinear phenomenon that the roll motion develops into large angle motion accompanied by heave and pitch in a short time after the ship encounters a specific wave.In random waves,parametric excitation roll is emergent,which means statistical analysis has strong non-ergodic property.And it is also sensitive to wave samples.Direct long-time duration tests and numerical simulations have great uncertainty,so that a more reasonable method is to evaluate the probability of encountered wave groups.Therefore,this paper establishes a set of numerical prediction methods from wave groups identification,wave groups simulation to ship parametric rolling analysis under wave groups.Firstly,the dangerous roll time segment is screened and the characteristic wave groups are identified based on the parametric parametric roll model test of C11 container ship at head seas.The relationship between the wave group and the ship parametric excitation roll is established,and the characteristic wave group excitation test is carried out.Then,a High-level Irrotational GN wave model(HLIGN)is introduced to simulate the characteristic wave group accurately.Considering the nonlinearity of the wave,the accuracy of IGN wave model is verified by comparing it with the characteristic wave group generated by the second-order nonlinear wave group test.A new method for the numerical construction of random wave group is established.Based on the mathematical model for wave group,the ship parametric rolling motion is predicted using the weakly nonlinear potential flow ship motion models.It is found that the parametric rolling is influenced by both the initial rolling motion and the characteristic wave group.Then,based on the catenary equation of mooring cable simulation model to verify the results of the wave group test in HEU,the study found that the ship parametric excitation roll is sensitive to test environmental conditions.The rolling motion changes greatly due to the change of external conditions,which further shows that parametric excitation roll has strong uncertainty.Finally,the frequency spectrum analysis of the response characteristics of the parametric excitation roll motion in the wave group was carried out and its occurrence mechanism was explored.It was concluded that the cause of the parametric excitation roll was the periodic change of the restoring moment caused by the encountered wave,and the incident wave length component inducing the parametric excitation roll was mainly located in the range of 1 to 1.5 times of the ship length.The primary frequency for the parametric rolling motion is located near 1/2 wave encounter frequency.