Mesh-free Method And Its Application On High-velocity Fluid Jet Impact And Penetration Simulation

To the high-speed impact problem, fluid-solid interaction, dynamical fracture and largedeformation problems, the large deformation will induce to the large distortion of the finiteelement mesh and made the reduction of precision even the termination of computation bysingularity; on the other hand, the computational time-step of FEA depended on the minimum sizeof mesh, the distortion of mesh made the time-step became very small, which made the wholecalculation time extended and the accumulated error increscent. Also the reconstruction of meshwill consume large computation cost in dealing with dynamical fracture problem. To overcomethese difficulties of FEA, the mesh-free method was developed in recent two decades and becamethe hotspot of computational physics and mechanics. By series particles without any meshstructure, the mesh-free method can avoid above difficulties of FEA.The main work of this paper focused on the algorithm and application of the mesh-freemethod. The process of mesh-free method included the computation of shape function, boundaryconditions and integral scheme and so on. The boundary characteristics of Kernel function, MLSmethod and RKPM was compared and the "virtual particle method" was presented to improve theboundary aberration of SPH. Usually the shape function of mesh-free method wasn't interpolationfunction, which was an obstacle to apply the essential boundary conditions. So the direct method,Lagrange multiplier method and point interpolation method were used to deal with the boundaryconditions and the result indicated the advantage of Lagrange multiplier method. Thecomputational example of cantilever illuminated the result sensitivity to the smoothing length ofsupport radius when use single point integral scheme in EFG method, however increase thenumber of integral points can decrease the sensitivity and improve the calculation precision.On the aspect of application of mesh free method, the Lagrange FEA method, ALE methodand SPH method was used to simulate the process of waterjet impact with the rigid surface, andthe comparison of result proved the merit of SPH from the point of precision and cost. Also theAluminum fluid jet impact with the rigid surface was computed, in which the voronoi cell wasadopted to assign the initial location and mass of particles, and the variable smoothing length wasconsidered. The process of Aluminum fluid jet striked the rigid surface and entered into the stableflow was analyzed; the result indicated the properties of wave propagation and dispersion.At the same time, on the base of fluid jet impact with rigid surface, the coupled SPH and FEAmethod was presented to simulate the impact and penetration of waterjet with plastic target. Theeffect of high strain rate and rate-dependent effect of target material were considered and theJohnson-Cook model was used in numerical simulation. By the simulation result of half-infinitetarget and middle-thickness target, the linear relation between jet velocity and penetration depthand radius was acquired which was consistent with the experimental data of literatures, and theresult also showed the process of fracture was developed with a limited speed, which was aprocess with energy accumulation and exhibited lag-effect under high strain rate load.The multi-scale theory combined RKPM and wavelet analysis was introduced in the last partof the paper, the multi-scale analysis was linked with shape function to construct the multi-scaleformulation of displacement and stress field. Also the adaptive algorithm of multi-scale RKPMmethod and the theory and application of wavelet finite element were introduced.