Study On The Wave Fields Generated By Diffraction Of Stokes Wave And Crescent Waves On Vertical Cylinder

In the environment of large wave,the nonlinear effect of the wave on the offshore structure is very significant.The nonlinear wave climbing occurs in the diffraction wave field around the structure,which will enhance the nonlinear slamming on the platform,and even cause the risk of overtopping and tilting.Therefore,different from the previous research which only gives the calculation results at the structure surface,this study pays more attention to the spatial distribution characteristics of wave height around the cylinder.Major works done in this thesis are as follows:Firstly,through the experimental analysis,the influence of water depth on the spatial distribution of Stokes wave diffraction field is studied,and the difference of spatial distribution between Stokes wave and the crescent wave is compared.The influence of the existence of the cylinder on the spatial evolution is studied by comparing the two cases with and without the cylinder.Then,based on the method of Green function and Eigen function expansion,the analytical expressions of second and third order diffraction potential and wave elevation of Stokes wave are derived.Finally,through the analytical expression,the amplitude spatial distribution characteristics of the first-order and second-order around the cylinder are given and compared with the experimental results.In order to calculate the second-order velocity potential efficiently and accurately,the spatial integral included in the velocity potential is calculated in different regions.Simpson numerical integral with variable step size and analytic integral are used to study the contribution of each part of the integral.The results are in good agreement with others.On this basis,the spatial distribution of the second-order wave height around the cylinder in different wave numbers is given,and the contribution of the first-order velocity potential product term and the second-order velocity potential to the second-order wave height is analyzed respectively,which lays a good foundation for the further study of the second-order wave field generated by the crescent wave around the cylinder.