Parallel Algorithm Of Time-discontinuous Material Point Method For High-velocity Penetration Problems

Penetration means the behavior of high-velocity projectiles such as fragments and bullets penetrate into targets,which plays an important role in the defense of our country and civil infrastructures.Some mechanical behaviors,such as nonlinear wave propagation,large deformation,damage and failure,fracture and heat softening arise from the penetration.As a meshfree numerical simulation algorithm,the Material Point Method(MPM)has natural advantages to solve penetration problems.In MPM,each body is discretized by a set of particles,so the fracture failure of structure is very easy to be simulated.MPM solves the momentum equation on the regular background grid nodes in each time step,which meads MPM needn`t to consider the problems caused by the grid distortion,so it is convenient to solve the large deformation process of the penetration problems.However,when the structures are subjected to impact loadings,the nonlinear wave will propagate in the structure.It leads to that the results of the traditional MPM often cann`t characterize the discontinuous characteristics and sharp gradient characteristics of the stress field accurately,and numerical oscillations arises near the wave front.In addition,with the increasing scale of the problems and the requirements for the high precision of the results,it is of great significance to develop a more efficient and accurate MPM.Therefore,in this paper,the studies of the problems of high-velocity penetration is mainly carried out as follows:Firstly,an parallel algorithm of explicit time-discontinuous MPM based on MPI is developed to solve the penetration problems,and the parallel program framework Explicit Material Point Method(ExTDMPM)is built.On the one hand,this algorithm combines the traditional MPM with time discontinuity effectively,which can characterize the discontinuity and sharp gradients of the stress field accurately,and control the numerical oscillations near the wave front.On the other hand,the communication between different cores is established based on MPI.ExTDMPM improves the computational efficiency obviously,has good scalability,and can solve problems with more than ten million particles.Secondly,the effects of different parameters on the time discontinuous scheme and the central difference scheme are analyzed.The results show that: with the increase of time step and the scale of material points,the time discontinuous scheme is more effect on controlling numerical oscillation;the parallel speedup ratio and efficiency of time discontinuous scheme are higher than those of central difference scheme,and the promotion effect of multi process on time discontinuous scheme is higher than that of central difference scheme;when the scale of material points reaches 10 million,ExTDMPM is still stable,and the efficiency of the program can still be maintained at 70%.Thirdly,the problem of projectile penetration is simulated successfully,and the influence of partition mode on program speedup is analyzed.Firstly,the Taylor bar example shows that ExTDMPM can simulate the dynamic problem accurate;secondly,the influence of partition mode on the parallel performance of ExTDMPM is analyzed by the low-velocity penetration of oval projectile into the target,and the results are compared with the experimental results;finally,the penetration of spherical projectile into the target shows that ExTDMPM has a good performance in the simulation of high-velocity penetration.