Nonlinear Numerical Simulation Of Motion Of Multiple Floating Structures In Waves

Offshore platforms,as equipment for exploiting deep-sea resources,are vulnerable to adverse effects of the harsh marine environment,resulting in intense movement during their work,which has adverse effects on the working environment of offshore platforms.Therefore,it is necessary to accurately predict the wave force and motion of offshore platforms in the early stage of design.At present,the research on wave forces and self-motion of offshore platforms under various sea conditions has been developed maturely.However,most commercial hydrodynamic software only considers linear theory or partial non-linear theory when simulating the interaction between offshore platforms and waves.Under adverse sea conditions,it has been unable to meet the accuracy requirements of engineering.Therefore,a fully non-linear calculation model of platform-wave interaction has been developed,it's very important.In this paper,a fully non-linear numerical program for open water is developed based on the linear boundary element method(LBEM)in the overall framework of potential flow theory.The Rankine source Green's function is used to discretize the computational fluid domain mesh;the motion equation is coupled by introducing virtual variables;the jet on the floating surface is treated by Taylor perturbation expansion method;the free surface mesh is optimized in real time by EMT technology;the non-linear free surface condition is considered,and the real-time position of the free surface is obtained by hybrid Euler-Lagrange method.The instantaneous wet surface mesh of the floating body is updated dynamically at each moment,and the reflective waves on the boundary of open water are absorbed by setting a sponge damping layer.By developing Fortran program,the variation characteristics of wave force and motion response of floating cylinder under different wave parameters are studied,and the accurate simulation ability of full-nonlinear numerical program is compared and verified.Finally,the multi-body hydrographic grid of semi-submersible platform calculation model is optimized,and the variation of wave force and motion response of semi-submersible platform under different wave parameters is studied.Chemical characteristics were studied.Offshore platforms,as equipment for exploiting deep-sea resources,are vulnerable to adverse effects of the harsh marine environment,resulting in intense movement during their work,which has adverse effects on the working environment of offshore platforms.Therefore,it is necessary to accurately predict the wave force and motion of offshore platforms in the early stage of design.At present,the research on wave forces and self-motion of offshore platforms under various sea conditions has been developed maturely.However,most commercial hydrodynamic software only considers linear theory or partial non-linear theory when simulating the interaction between offshore platforms and waves.Under adverse sea conditions,it has been unable to meet the accuracy requirements of engineering.Therefore,a fully non-linear program for calculating the interaction between platforms and waves has been developed.It's very important.In this paper,a fully non-linear numerical program for open water is developed based on the linear boundary element method(LBEM)in the overall framework of potential flow theory.The Rankine source Green's function is used to discretize the computational fluid domain meshes and to resolve the singularity of the boundary integral equation by splitting the meshes.The fluid pressure is solved indirectly by introducing virtual variables,and the motion equation is solved by coupling.The Taylor perturbation expansion method is used to deal with the jet formed on the surface of the floating body when the wave nonlinearity is strong.The EMT technology chooses suitable elastic constitutive relation to optimize the free surface mesh in real time,and verifies its validity by numerical simulation,which guarantees the quality of the mesh in the simulation of non-linear phenomena,smoothes the free surface mesh by five-point smoothing method,and reconstructs the free surface mesh according to a certain wave period,and adopts mixing method by considering the non-linear free surface condition.The Euler-Lagrangian method captures the real-time position of the free surface.The non-linearity considered in this paper is mainly the non-linearity of the free surface and the object surface,so the instantaneous wet surface mesh of the floating body is updated dynamically at every moment.A sponge damper layer is set on the boundary of the open fluid region to absorb the reflected waves on the boundary of the open water region.In this paper,after the development of full-nonlinear numerical program in open water based on Fortran language,the validation of different scale models,the verification of fixed floating body model and the convergence analysis of mesh lay the foundation for the follow-up study using full-nonlinear program.In this paper,the variation characteristics of wave force and motion response of floating cylinder under different wave parameters are studied by using the developed fully non-linear program.Then,the motion response of floating cylinder under different wave conditions is compared with the results in frequency domain.The flow field changes and the motion of floating cylinder are visualized by MATLAB software.Based on the floating cylindrical mesh model,a multi-body free-surface mesh model suitable for the simulation of multiple floating structures is constructed,and the effects of incident waves with different wave parameters on the wave force and motion of multiple floating structures are studied.