A Study On The Statistical Law Of The Particle-bed Impact Process And Its Sensitivity To Characteristics Of Particle Bed

The medium composed of particles exists widely in nature and industry.Its complex macro-mechanical behavior is the result of the contact and collision process between a large number of particles.The foundation of studying the macroscopic mechanical behavior of this kind of granular medium needs to be based on the understanding of particle-particle collision and particle-particle bed collision mechanical behavior and their laws.Among them,for the evolution and development of wind-sand flow,the mechanical behavior of particle-particle bed collision plays an important role.Aiming at this basic problem,this article uses numerical simulation to study the influence of the characteristics of the particle bed on the mechanical behavior of particle-particle bed collisions.The specific contents include:The second chapter of the thesis compares and analyzes several existing particleparticle collision models,including linear elastic damping model,artificial damping model,Hertz model,viscoelastic model and three different elastoplastic models,including Zhou model and Thornton model,analyzed the dependence of the particleto-particle collision recovery coefficient of several models on the relative collision velocity,compared the rationality of several models,and found the elastoplastic model Among them,the Thornton model,Thornton model with stress strengthening and Zhou model.The latter two models are highly correlated with the experimental results,while the Thornton model is different from the experimental results.In Chapter 3 of the thesis,a monodisperse and polydisperse one-dimensional ball chain model is established.Numerical simulations are used to study the collision dynamics between the incident bead and the spherical chain,while the impact velocity,chain length and particle size of the incident bead are studied.The influence of parameters such as ratio on the rebound to incident speed of first bead,the coefficient of restitution and other mechanical parameters are analyzed.The study found that with the chain length increases,whether it is a monodisperse chain or a multi-dispersed chain,the coefficient of restitution of the first ball and the first pair of beads will reach a constant.In the case of a monodisperse chain,the coefficient of restitution of the incident bead has a non-linear relationship with the incident speed.For a chain of certain length,the coefficient of restitution will reach a "terrace" stage.But in a multidispersed chain,the coefficient of restitution of the incident bead tends to be constant as the chain length increases.Parameters such as the rebound velocity of the first bead are also related to the particle size and the initial velocity.In Chapter 4 of the thesis,a two-dimensional particle-particle bed collision model is established.Considering the different particle size distributions of the particle bed,the discrete element method is used to numerically simulate the particle-particle bed collision dynamics process to study the incidence of incident particles.The impact of velocity and particle size distribution characteristics of the particle bed at the point of incidence on collision dynamics.Our numerical simulation study found that: firstly,for a particle bed composed of particles with a normal distribution of particle size,different standard deviations under the normal distribution will affect the entire collision process;secondly,the geometric mean center of the ejected particles will change with the incident angle and incident speed,and the speed of ejecta also change with the change of their relative positions.The farther away from the incident particles,the lower the speed of ejecta.The fifth chapter of the thesis discusses the remaining problems in the research,and prospects the possible further work.