Analysis And Program Design Of Particle Breakage Process In Discrete Element Method

The safety of launching charge has been widely concerned by the domestic and foreign weapons industry.With the crushing and breaking of the initial propellant bed in the internal ballistics,the bore is easy to burst.The degree of fragmentation of the propellant bed under high stress has become the significant problem in the study of the safety of launching charge.Propellant bed is essentially a granular system which consists hexagonal prism particles.Based on the discrete element method,this thesis systematically studies the program implementation of a granular system with the crushing of polyhedral particles,and applies it to the study of the fracture process of the propellant bed under high impact loads.The main research contents of this thesis are as follows:1.The basic theory and fragmentation model of discrete element method are studied.A polyhedral particle fragmentation model based on spring-tetrahedron is proposed to improve the accuracy of the discrete element method for describing the true shape of complex particles and fragments.2.Two kinds of contact detection algorithm in the discrete element program is discussed in detail.In the neighbor list algorithm,the Verlet List method,the Linked Cell method,the LLL method are studied.In the precise contact detection,and the Common Plane method,the GJK method and the Ray Crossing method are analyzed.According to the characteristics of the polyhedral particles,the LLL method is selected to establish neighbor lists.Through programming and comparing the characteristics of the GJK method and the Ray Crossing method,the thesis concluded that the GJK method has higher efficiency but the stability of the Ray Crossing method is better.3.A discrete element program which is capable for simulating a granular system with the destruction of polyhedral particles is developed.In the main program,the implementation of information initialization,loop calculation and memory release is described in detail;the main process of the graphics post-processing program with OpenGL and the code implementation of the image are explained;by simulating the falling of the cubic particles,the free down of non-convex particles.The effectiveness of the program and the fracture model is verified by the fructure of a single cubic particle and cubic particle system.4.The numerical simulation of the fructure process of the propellant bed is carried out and compared with the physical experiment.A discrete element model of propellant crushing is established.The compacted structure of the propellant bed is obtained by the program without fracture model.The fructure program is used to establish the single-particle fragmentation model of the propellant and the propellant system of the propellant bed.A statistical rule of the fragmentation degree for the spring-tetrahedron model is established;the simulation and analysis of the single particle fracture of the propellant under different impact loads,the simulation results of the particle fracture and the crushing process are consistent with the physical test results;the propellant bed is simulated according to the real load,and the simulation results are good correspond with the experimental results.The verification analysis of the program shows that the discrete element program and the fragmentation model are effective.Compared with the same physical experimental results.The simulation result of the single propellant particle crushing process is precise.The program of the granular system that can simulate the fragmentation of polyhedral particles is established and it could provide important theoretical support and research methods for launching charge safety research.