Research On Fully Nonlinear Numerical Wave Flume Model With Domain Decomposition Method

With the progress of the world's marine development technology and the continuous expansion of the scope of development,a more severe development environment means that the nonlinear effects of waves faced by marine engineering structures are also more significant,and the challenges faced by the development of marine resources will become increasingly difficult.Based on the theory of potential flow,this paper establishes a threedimensional wave tank time-domain numerical model using the high-order boundary element method(HOBEM)to explore the nonlinear phenomena of wave-body interaction.The numerical flume model uses the fourth-order Runge-Kutta method to realize the time stepping process of the free water surface and the object surface,uses the spring approximation method to divide the instantaneous free water surface grid and the object surface grid,and uses the acceleration potential method to calculate the wave force.A domain decomposition method is used to reduce the cost of simulating the propagation and diffraction calculation of a fully nonlinear regular wave around a fixed vertical cylinder.The domain decomposition method needs to realize the continuous boundary conditions on the interface between adjacent subdomains.By adjusting the iterative process on the interface,four different coupling methods are established by using the condition types of different coupling methods(Dirichlet boundary condition or Neumann boundary condition),called D/D-N/N method,D-N method,N-D method and mixed D-N/N-D method,the main difference between the four methods lies in the different matching schemes of the boundary conditions at the left and right ends of the subdomain interface.The comparison of different domain coupling methods shows that compared with the single domain method,the domain decomposition method can also provide accurate results.For the wave propagation problem,by changing the number of subdomains and the number of units,it can be known that the number of subdomains exceeding a certain limit in the domain decomposition method will increase the CPU calculation time.After comparing the calculation efficiency of different coupling methods,it is recommended to use D/D-N/N coupling.Method to solve the wave propagation problem.For the interaction between waves and floating bodies,the hybrid D-N/N-D coupling method can obtain the highest calculation efficiency.And with this sub-domain method,the problem of the forced motion of the truncated cylinder in the flume is studied.The increase of the motion amplitude and draft of the floating body heave motion will cause the nonlinear phenomenon of wave load and wave climb to be more obvious.When the motion is violent,the contribution of high frequency such as triple frequency can no longer be ignored.The increase in the amplitude of the floating body swelling motion has little effect on the horizontal force and the torque around the y-axis.The nonlinear phenomenon is mainly concentrated in the vertical force.The main contribution of the wave run-up at the lateral measurement point of the tank near the floating body is the double frequency.And it is easily affected by the cylinder amplitude and draft.In the problem of the interaction between the floating body and the wave,the side wall of the flume will enhance the generation of nonlinear phenomena in the problem of the interaction between the floating body and the wave to a certain extent.Through the analysis of the results,it can be shown that in the problem of the interaction between the floating body and the wave,the increase in the intensity of the movement will cause the higher-order effect to become more and more obvious,and the contribution of the high-frequency region cannot be ignored.A fully nonlinear model with higher accuracy is more reliable than a frequency domain calculation model to deal with such problems.