Some Study On Static And Dynamic Behavior Of Granular Systems Based On Discrete Element Method

Granular matter is widely encountered on the earth and inseparable with our daily life, which usually exhibits many complex static and dynamic mechanical behaviors with special physical phenomena. Because of such special features, granular material has become a hot and difficult problem what is in the face of academy and engineering. The macroscopic behavior of granular material is mostly dependent on the interaction operation between particles. In order to explore the macroscopic static and dynamic properties, granular material can be investigated on the basis of micro-mechanical consideration, for example, the feature of fabric, distribution of contact force network, and motions of the particles. Based on the discrete element method, this thesis mainly simulates some static or dynamic phenomena in granular matter. Through analysis and statistics of micro-mechanical properties of the particles, we investigate the influence of micro parameters of particles and external excitation on the macroscopic static and dynamical responses of granular matter. The main works are concluded as follows,Firstly, the phenomenon of stress dip is investigated. We introduce the clump which represents kinds of particles with different aspect ratios and the formation process of granular pile in simulation using fixed height point method. Moving average statistical method is used to analyze the pressure on the base, which shows the pressure dip in the vertical direction and inverted-S style in the horizontal direction. Then the anisotropic characteristics of particle orientations, contact orientations and contact forces are analyzed. The simulation results show that the arches are formed to shield the center from some of the weight, which generates the pressure dip. For large aspect ratio, higher inclination of the arches is possible and higher contact force is achievable in the arches, this would therefore exaggerate the pressure dip.Secondly, through biaxial tests, several contact models are adopted in the simulation to study the effect of the micro parameters of particles on granular matter. The sample generation method and strain boundary condition are present. Conventional discrete element method, modified discrete element method and clump method are used respectively to analyze the distributions of contact orientations and contact forces. The ideal elastic-plastic relationship is shown in deviatoric stress and axial strain curve for smaller friction coefficient and softening behavior appears for larger friction coefficient. The angle of internal friction and the shape parameter show an approximate linear relationship. The relationship between angle of internal friction and the friction coefficient obeys power function. Ours results are quantitatively consistent with existing results, and can provide an important theoretical parameter adjustment in simulation.Finally, the motion characteristics of monolayer spheres under swirling drive are studied. Through comparison with experiment results, the reliability of our program has been verified, and the values of the parameters are determined. We analyze the relation between the Liquid-solid phase transition and filling fraction, and analyze the effect of the particle properties and driving parameters on the critical filling fraction. With filling fraction increasing, the distribution of particle velocities changes gradually from Gaussian distribution to exponential distribution. The segregation occurs in appropriate range of the filling fraction. If the obstacle is fixed in the dish, the obstacle has an important effect on particle migration speed and the separation range of filling fraction. The results would be applied in the remixing and separation of the particles in chemical and pharmaceutical fields.After all, simulation research on the characteristics of contact orientations, contact force and base pressure in granular piles made of the particles with different shapes, research on macroscopic mechanical responses of the granular system using biaxial tests, and research on the motion characteristics of monolayer granular cluster under external excitation, the characteristics of evolution of granular system are revealed. Moreover, such fundamental researches can provide some basic analysis methods and quantitative results for geological, chemical, energy, and pharmaceutical engineering, et al, and it is very important to improve the research framework of mechanical system.