A CIP-based Fluid-structure Interaction Model And Its Application

Hydroelastic phenomena like whipping and springing of marine structures often occur in rough sea conditions.In these phenomena,the violent flow causes impulsive impact and cyclic force on the structures,which can cause serious damage to the structures,or even instability.Complex problems will arise in hydroelastic phenomena such as splash of liquid and large deformation of structures,which make it almost impossible to be solved with analytical methods.Also,it is time consuming,high-cost and demanding of measuring instruments to study problems mentioned above by experiments.Numerical simulation becomes an important method to analyze hydroelastic problems.FDM-FEM coupled method can not only effectively capture the drastic changes of free surface without grid distortion,but also build complex boundary easily,which leads to unique advantages in simulating fluid-structure interaction phenomena.Main difficulties of the method lie in coupling numerical scheme of both structures and fluid.The aim of this study is to introduce a new strategy to couple FDM and FEM,and apply it to study engineering problems related to hydroelasticity.Firstly,both structural solver and fluid solver are introduced.A finite difference scheme based on Constrained Interpolation Profile(CIP)is developed to solve the flow field.The fluid model has shown well efficiency and accuracy in solving Navier-Stokes equation.Volume of Fluid(VOF)method is applied to reconstruct free surface in this model.The nonlinear deformation of the solid structure is solved by co-rotational method based on Finite Element Method(FEM).The structural solver is used to analyze the nonlinear deformation of cantilever beam under static loads and the structural response under dynamic loads.The feasibility and precision of the structural solver in solving large deformation of structures were verified.Then,the Immersed Boundary Method(IBM)based on ghost cell method is introduced to couple structural solver and fluid solver.In the handling process,the fluid-structure boundary position can be marked out by ghost cells.Information of ghost cells can be calculated through "interpolation by six points" process,and the non-slip boundary condition can be satisfied automatically.Elastic plate subjected to time-dependent water pressure and interaction between plate and sloshing were simulated through modified FDM-FEM coupled method.The numerical results are in agreement with published results.Also,results of this paper were compared with results of traditional FDM-FEM coupled method,which show that the modified FDM-FEM coupled method can capture structural response more accurately.Finally,the modified FDM-FEM coupled method was used to study wave absorbing property of the elastic vertical plate and vortex suppression characteristics of the elastic diverter plate attached with a cylinder.For the former,results show that elastic diverter plate can reduce the drag force and vortex frequency of the cylinder,compared with that of rigid diverter plate.Under a certain material stiffness,"first mode" and "second mode" of structural vibration will appear successively as the plate length increases.For the latter,results show that the length of plate has a great influence on the wave elimination performance of vertical plate.The wave dissipation performance of rigid plate is better than that of elastic plate with same length.