Numerical Simulation Of Water Entry Problems By Using The WCSPH-SPIM Coupled Method

The research on the water entry has important practical significance in the field of ship hydrodynamics and ocean engineering.The process involves the instantaneous strong nonlinear slamming.In many cases,the influence on the structure is obvious.There will be fluid structure coupling effect accompanying slamming process,which increases the difficulty of calculation.In this paper,WCSPH-SPIM coupled method based on fluid-solid interaction(FSI)idea is used to simulate the water entry problems of ships and other structures.As a typical representative of the meshless particle method,the Weakly Compressible Smoothed Particle Hydrodynamics(WCSPH)method possesses the Lagrange property,which is prominent in the application of the impact problem involving free surface,coupled with the Smoothed Point Interpolation Method(SPIM),which is suitable for complex structures and large deformation problems.Then,the virtual particles are introduced to construct the WCSPH-SPIM FSI solving program.Firstly,the WCSPH and the WCSPH-SPIM FSI method are respectively verified by the rigid water entry,the inclined plate low-speed water entry and the wedge high-speed water entry.The results are consistent with the experimental results or semi-analytical solutions,the pressure distribution is uniform and the free surface details are accurately depicted.Therefore,it is verified that the WCSPH-SPIM FSI program has the ability to simulate the water entry problem of elastic structures.Secondly,a series of improvements are introduced,including pre-processing optimization,coordinate transformation and precise processing of FSI forces,so that the WCSPH-SPIM program can solve the complex water surface and inclined water entry problems.The improved program is used to calculate the force,deformation and flow field evolution of the concave,convex,ordinary wedge and recurved surfaces under the same other conditions.It is considered that the instantaneous pressure of the ordinary wedge is less than that of convex and concave,and the deformation is less than that of recurved,so the performance of decreasing the instantaneous impact pressure is the best.Finally,the influence mechanism of A and B type of asymmetric entry impact caused by kinematic asymmetry and geometric asymmetry is studied,the simulation of rigid body asymmetry is compared with the experimental results,and the free surface configuration is in good agreement with the experimental image.The greater the horizontal-to-vertical speed ratio as well as the angle of inclination,the more likely it is to cause B impact.After the wedge is given to the characteristics of elastic material,the asymmetric water entry problem under various conditions is simulated.It is concluded that the elasticity has little effect on the transformation of AB impact,and it mainly act on the side of the inflow to bend the wedge,thus changing the pressure distribution in the high pressure area.