The Numerical Simulation Of Extreme Waves With Coupling Model Based On High-order Spectral Method And CFD

Extreme waves are strong nonlinear waves with unusual wave heights and asymmetric shapes.Encountering extreme waves has been one of the most important causes of severe damage to ships and offshore structures.The numerical simulation of the formation and evolution of extreme waves could help solve the problem of interaction between extreme waves and structures better,which is of great significance in ensuring the safety of people and property at sea.In this thesis,the efficient simulation of wave evolution and extreme wave generation is based on the high-order spectral(HOS)method.And the extreme waves are reconstructed in the CFD calculation domain by the construction of coupling model.First,the control equations,boundary conditions and calculation flow of two models based on HOS methods are introduced which are HOS-ocean and HOS-NWT.The accuracy and stability of these models on the simulation of wave propagation are verified by standard calculation.Then in the existing HOS-ocean model the function of wave field initialization simulation based on ITTC2-parameter spectrum is introduced,which has been verified by spectral analysis.Then based on the HOS-ocean model,this thesis simulates extreme waves in two method.One is by the adjustment of the phase of each wave component at the initial moment to form a focused wave at a fixed time and position.Another one is by long time nonlinear wave evolution of large-scale wave field to obtain extreme waves.After long time simulation of large-scale wave fields with different directionality,it isfound that the stronger the directionality of the wave field is,the larger the mean lateral wavelength of the extreme wave becomes.This thesis realizes the construction of the coupling model based on HOS method and CFD calculation,including the setting up of relaxation zone,the selection of interpolation model,the design of interface module and whole calculation process.The various basic types of waves calculated by the HOS model are reconstructed in the CFD computational domain,which could verify the accuracy of the coupling model.Then,based on the flow field information around the extreme waves calculated by the HOS model,the coupling model reconstructs the wave field in the region.In this way the focused wave,as well as the extreme waves in large-scale wave field are reconstructed in CFD calculation domain.Finally,the thesis applies this coupling model to analyze the velocity distribution of the internal flow field near the peak and trough of the constructed extreme wave.It is found that the velocity component has a strong concentration in the main direction of wave propagation at the moment of extreme wave appearance.