The New Computational Method Of Second Order Diffraction Potential In Outer Region

The action of ocean engineering structure and nonlinear wave load is an important research subject.The wave action of vertical circular cylinder resting on seabed is often used in ocean engineering is main exterior load.The second-order wave force is one of main investigating directions of numerical simulation.Many investigations have shown that when the incident wave is a Stokes wave,the second order force caused by the second order velocity potential is dominant.So in this case,the accurate calculation for the second order velocity potential is a critical problem for the accurate calculation for the second order force. The main difficulties are following:First,the adoption of the second order radiation condition; Two,the link up of inter and outer region;Three,the expression in the outer region.In this article,This article will make the further studies under the predecessor's foundation,looking for the simple analytical expression in the outer region,the main work of this article are following:First:Solving the problems of first and second order diffraction using Boundary element method.The method is based on the boundary element method using 1/r type Green function in the inner water region,combined with the eigenfunction expansions in the outer region.Then it can solve the question of infinite integral in second order free surface condition.For the problem of the second order radiation condition,the second order radiation condition is posed for the circumferential Fourier components of second order potential.Second:A new computational method of second order diffraction potential in outer region is established.This method is based on reducing order formula of Hankel which can be used to deal with the irregularity of Hankel function in eigenfunction expansions of second order diffraction potential.Then the computational method make the eigenfunction expansions clearer and more convenient.By comparing the value of second order diffraction potential with the former value,we can review the validity of this method.Third:Comparing the first order force,second order steady force and second order oscillating force,which can validate the precision of this method.Further,the value can prove the numerical method of this article is effective and the computational method of second order diffraction potential in outer region is feasible.