Study On FEM-SPH Coupling Method For Simulation Of Fluid Structure Interaction Problems

Fluid structure interaction problems exist widely in practical engineering,such as flapping wing of bionic bird,wave impact on structure,sloshing of fuel in tank,interaction of valveless micropump and pump diaphragm.The numerical method for studying fluid structure interaction has important application value.The most widely numerical method of simulating fluid structure interaction problems is that using the Lagrange scheme to simulate the solid domain,such as finite element method(Finite element method,FEM),and using the Euler scheme to simulate the fluid domain,such as finite difference method,finite volume method and finite element method.In recent years,the simulation of fluid structure interaction problem under pure Lagrange scheme has great attraction because it can naturally track the motion deformation interface,and without no convection term.FEM-SPH coupling method is a method of simulating fluid structure interaction problem in pure Lagrange’s form by using FEM method to simulate solid domain and using SPH(Smooth particle hydrodynamics)method to simulate fluid field respectively.The FEM method has advantages in simulation of solid and the SPH method has advantages in the simulation of free surface flow.The FEM-SPH coupling method can make full use of the FEM method and SPH method.The FEM-SPH coupling algorithm for simulating fluid structure intereaction problems is studied in this paper to providing an alternative way to simulate the fluid structure interaction problems in pure Lagrangian.In this paper,the SPH method is improved in the aspects of efficiency and stability.On the basis of this,the FEM-SPH coupling algorithm for simulating fluid structure interaction problem is studied systematically.The work completed in this paper is as follows:(1)The basic theory of SPH method is introduced.The instability of SPH is studied in fluid simulation,which mainly includes the instability caused by pressure shock and the instability caused by uneven particle distribution.The computational accuracy and stability are improved by using a combined correction method.The neighbor particle search algorithms of the link list search algorithm and the strip PIB search algorithm are studied,the link list serch algorithm and the S-PIB algorithm are improved.The efficiency of algorithms are compared.(2)The FEM-SPH coupling algorithm of fluid srtructure interaction is studied.The advantages and disadvantages of each FEM-SPH coupling algorithm are analyzed,and an improved FEM-SPH coupling algorithm is proposed.The FEM-SPH coupling algorithm based on the Johnson master-slave contact algorithm,the FEM-SPH coupling algorithm based on repulsive force and the coupling algorithm based on the ghost particle are analyzed in detail,and the advantages and disadvantages of each FEM-SPH coupling algorithm are pointed out.On this basis,a FEM-SPH coupling algorithm based on repulsive force and ghost particle is proposed.A FEM-SPH coupling algorithm code is developed to simulate fluid structure problems.Numerical examples are used to compare the contact algorithms,and the effectiveness of the coupling algorithm based on repulsive force and ghost particle is verified.(3)The new ghost particle technique has been developed to deal with complex geometries and large deformation interfaces.The FEM-SPH coupling method based on ghost particle can obtain higher precision than other methods,however,the ghost particle method is difficult to deal with complex geometries and large motion deformation boundaries.In this paper,a ghost particle method for dealing with complex geometries and large motion deformation boundaries is proposed.Based on the ghost particle method,a FEM-SPH coupling algorithm is proposed.(4)Two pressure solving methods of FEM-SPH coupling algorithm are compared.WCSPH(Weakly compressible SPH)and ISPH(Incompressible SPH)are two methods for imcompressible fluid.ISPH method solves the pressure through the pressure Poisson equation,and does not appear the pressure oscillation,and the pressure result is more accurate than the result obtained by the WCSPH method.The FEM-WCSPH coupling algorithm is compared with the FEM-ISPH coupling algorithm.(5)A three-dimensional FEM-SPH coupling algorithm code for simulating fluid structure interaction problems is developed.A three-dimensional FEM-SPH coupling algorithm based on ghost particle and repulsion force is developed.Based on OpenMP,a parallel program of 3D FEM-SPH coupling algorithm is developed,which improves the computational efficiency.The effectiveness of the program is verified by numerical examples,and it lays the foundation for the application of FEM-SPH coupling algorithm to simulating fluid structure interaction problems in practical engineering.