A Study Of Three-dimensional Fluid-structure Interaction Problems Based On The Immersed Smoothed Point Interpolation Method

Three-dimensional fluid-structure interaction(FSI)problems especially with largely deformable or movable structures has been one of the most difficult and hottest subjects to be solved.Immersed smoothed point interpolation method(IS-PIM)introduces the fictitious fluid to separate the fluid field and solid field.The fluid field and solid field are meshed by Euler grid and Lagrange grid,and they are solved by using well-developed characteristic-based split(CBS)method and Smoothed Point interpolation method,which avoids the trouble reconstructing the grid.The method adopts flexible triangular or tetrahedron grid that both can be automatically meshed to shorten the preprocessing time,improving the efficiency of IS-PIM.The traditional finite element method(FEM)suffers the low accuracy problems due to the overly stiffness model of solid,adopting the unstructured grid.However,S-PIM has been proved to soften the stiffness model of solid through gradient smoothing technique and improve the accuracy of solving solid equations.In order to compare the performance of different solid solvers,FEM,edge-based smoothing point interpolation method(ES-PIM)and node-based partly smoothing point interpolation method(NPS-PIM)were compared to each other in terms of accuracy and efficiency.Results show that adopting S-PIM as solid solver can obviously improve accuracy and efficiency.Based on that,in order to put IS-PIM into solving three-dimensional FSI problems,3D IS-PIM adopts face-based smoothed point interpolation method(FS-PIM),easily to be constructed.IS-PIM has been verified to solve 3D FSI problems appropriately and accurately through three classical FSI examples.The outermost FSI information of solid cannot be transmitted into the fluid accurately due to the separation between solid and fluid,influencing the accuracy of solving 3D FSI problems.In order to improve the present deficiency,3D IS-PIM employs sharp-interface methods to correct the boundary of FSI problems.And this method has been proved to alleviate the problem that streamlines flowing through the cylinder,through the example of flow around circular cylinder,improving the accuracy of solving 3D FSI problems.Finally,based on 3D IS-PIM after boundary correction,some parametric study has been done about flow control problems.Study shows that the drag force and the fluctuation of lift force can be obviously decreased by attaching a stiffness flank behind the cylinder of flow around circular example,which also alleviates the shedding of trailing vortex.The length of the flank L* equals to 1.5 behaves best in the current context.The distance l* between this flank and the cylinder gradually gets bigger,and the drag force and the fluctuation of lift force both decrease most when l* equals to 2.5,which is proved to be the most appropriate distance in the current context.Besides,study also shows that the drag force and the fluctuation of lift force change in the same way with the distance ? between two tabs getting bigger,which are layout symmetrically up and down the cylinder,and they both decrease most when ?=3.7.