Application Of Nonlinear Wave Theories For Wave Generation In A High-order Spectral Numerical Wave Tank

High-order spectral(HOS)method is a numerical method for simulating the evolution of water waves based on potential flow theory,in which the velocity potential function is expanded into Fourier series satisfying the governing equation and periodic boundary conditions,and fast Fourier transform(FFT)is used to calculate the products in spatial domain and wavenumber domain.High-order spectral method exhibits high level of accuracy as well as efficiency properties,while its application to wave dynamics is limited to periodic unbounded domains.A high-order spectral numerical wave tank can be built by using additional potential function to bring non-periodic wavemaking boundary condition into HOS method.First,this dissertation uses stream function wave theory to calculate the boundary's inlet velocity numerically,and integrates it into the high-order spectral numerical wave tank.Thus,this numerical wave tank model's wavemaking boundary condition and free surface boundary condition are both fully nonlinear.Different regular waves have been studied numerically by using this numerical wave tank model,and the results are compared with analytic solutions and other numerical results.The comparisons show that this numerical model has the advantages of high accuracy and high computational efficiency.Second,for irregular waves,wavemaking boundary's inlet velocity can be obtained by 2nd-order stokes wave theory,then the simulation of nonlinear irregular waves is realized.In order to verify the accuracy of numerical wave tank model for irregular wave's simulation,the numerical results are compared with the theoretical solution and the high-order boundary element method's numerical results.Finally,nonlinear regular and nonlinear focused wave's forces on vertical wall are studied by the numerical wave tank in this dissertation.The influences of wave steepness,water depth and wave frequency width of focused wave group on the wave forces are also analyzed.In this dissertation,the inlet velocities strictly satisfy the incident boundary condition of nonlinear waves,reducing the generation of unnecessary wave components,so the high-order spectral method numerical wave tank can simulate nonlinear regular waves and irregular waves efficiently and accurately.