Application Of MPS-FEM Coupled Method In Fluid Structure Interaction Problems

In the nowadays,more and more ship and marine structures are manufactured and inevitably operated in rough sea.Vibrations and deformations of these structures will be induced by the wave loads,and may pose severe challenges to the structural security.In the previous researches,these fluid structure interaction(FSI)problems have not been solved thoroughly since there are several characteristics which are difficulty to be analyzed.First,muti-physics are included in the FSI problems.The solid physic,the liquid physic and the gas physic should be discribled within a coupling system instead of seperated ones,and a direct or iterative solution is essential for the coupling system.Second,the nonlinear behaviors of free surface of water and deformation of structure are usually difficulty to be modeled.Besides,the characteristic time scales concerning the fluid motion and the structural response are obviously different.For instance,the period of liquid motion can be dozens of times larger than the structural vibration period induced by the impact loads for the FSI problem of liquid sloshing in a large tank.To capture the characteristics of FSI problems thoroughly,it is of great scientific and practical significance to develop a method for the these problems in the ship and ocean engineering.In this paper,the MPS(Moving Particle Semi-implicit)and FEM(Finite Element Method)coupled method is proposed for the numerical investigations of FSI problems in the ship and ocean engineering.Herein,the MPS method which is formulated within the Lagrangian system is good at the simulations of violent flow and large motion of structure.Therefore,this method is employed for the analysis of the flow domain in the FSI problems.In our previous researches,several improvements regarding both the computational accuracy and efficiency of the MPS method have been conducted.As a result,the application scope of this method in ship and ocean engineering can be expanded,and it prepared the foundation for the numerical study of FSI problems by the MPS-FEM method.To realize the coupling between the MPS method and the FEM method,this paper proposes a partioned coupling strategy with the time asynchronous characteristic.With the help of this strategy,the numerical calculation process,which takes the advantages of the two approaches in simulating the flow domain and the structural domain respectively,is developed.In this strategy,different time step sizes can be employed for the simulations of the two computational domains.For the simulation of a three dimensional FSI problem by the MPS and the FEM methods,the fluid domain should be dispersed by the particle model while the structure domain should be dispersed by the grid model.Since the heterogeneous feature of the two models,the data transmission is hard to be realized on the interface between the two physics.To overcome this chanllenge,two interpolation techniques for the data transmission are proposed in this paper,which are the shape function based interpolation technique and the kernel function based interpolation technique,respectively.With the help of the partioned coupling strategy and the two data interpolation techniques,the MPS-FEM coupled method is proposed and can be applied into the 2-D or 3-D FSI problems of the ship and ocean engineering.Based on the aforementioned MPS-FEM coupled method,an in-house FSI solver MPSFEM-SJTU is developed in the present study.The FSI solver is mainly consisted of three modules,the MPS module,the FEM module and the data interpolation module.Herein,the first module is based on the MLParticle-SJTU solver,which is a MPS solver aim to simulate the violent flow with free surface.With the cooperation between the three modules,the solver can be used for both 2-D or 3-D FSI problems.Before widely appling the FSI solver in the ship and ocean engineering,a series of FSI benchmarks are numerically studied to validate the accuracy of the solver.For the 2-D FSI problems,the phenomena of the dam-break flow interacting with an elastic gate,the dam-break flow impacting onto an elastic wall,etc.,are simulated and good agreements are achieved between present results and experimental results.Besides,the capability of the FEM module for the 3-D structural response problem is also investigated.The vibration of an elastic thin plate,which is dispersed by squre elements,is calculated and the results agree well with those calculated by the ANSYS software.In addition,the experimental tests for the data transfermission on the heterogeneous interface between the two physics are conducted,and the computational accuracies of the interpolation technique based on shape function and the interpolation technique based on the MPS kernel function are verified.All these validation results show that the solver MPSFEM-SJTU is accurate and reliability enough for the numerical simulation of FSI problems.After these validation researches,the solver MPSFEM-SJTU is applied into the FSI problems of liquid sloshing flow interacting with 2-D elastic structures.First,sloshing phenomenon in an elastic tank,which is filled by water with low height rate,is numerically studied.By changing the Young's modulus of the bulkheads,the influence of structural stiffness on the slamming phenomenon induced by the motion of sloshing waves is investigated.The characteristics of impact pressure,structural deformation and modes of vibration responses are comparatively analyzed.Then,the FSI phenomenon induced by the roof impact events within an elastic tank of high filling ratio of water is simulated,and the characteristic of high frequency vibration of the roof bulkhead are presented.In addition,the influences of the elastic baffle on the sloshing flows are also investigated under a series of excitation frequencies of the liquid tank.In this paper,the solver MPSFEM-SJTU is also applied to the 3-D FSI problems.For instance,the applicability of the solver in 3-D FSI problem is tested by the simulation of dam-break flow impacting onto the elastic lateral wall of the flume.Then,the liquid sloshing within a 3-D tank filled with low height of water is simulated.Herein,the elasticity of the lateral walls of the tank has been taken into considered in the simulation.The structural response induced by the impact loads of the sloshing wave and related free surface evolution are presented.The 3-D effects of the sloshing phenomenon are illustrated by the liquid motion and structural deformation.