Theoretical Investigations On Some Characteristics Of Macro-Mechanics Of Dense Granular Systems Based On Discrete Element Method

Granular matter is widely encountered in the nature and engineering applications, and usually may exhibit many complex and special features. At present, studies of granular material have become a very important research field as such matter has wide applications and scientific implications. The macroscopic behavior of granular material is mostly dependent on the interaction operating between particles. So the understanding on the fundamental properties granular material can only be obtained on the basis of micro-mechanical consideration, for example, arrangement, contact, collision and motion of the discrete particles in space. Based the modified discrete element method, this thesis mainly investigates the localized deformation of stochastic distributed granular material under plain strain conditions and dynamical features of shearing granular flow. Though analysis and statistics of micro-mechanical quantities, we investigate deformation and flow features of granular system on the macro scale. At last, we also investigate the distributing and evolution features of contact force network in dense granular systems. The main works are concluded as follows:Firstly, Considering the rolling resistance between particles, a modified discrete element model(MDEM) is established to simulate the dense granular system. For different packing fractions and loading conditions, we have presented several specimen generation methods. The influences of boundary stress, initial configuration, loading rate and friction coefficient between particles on the state and configuration of dense granular system are also examined. Moreover, the features of the localized deformation in stochastically granular material are investigated under plain strain conditions, and obtained pattern of the macro deformation is well consist with measurements. The numerical results show that various material parameters or factors have significant influences on localized deformation features, capacity of carrying loading and whole stability of granular materials.Secondly, based microscopic motions of particles inside granular system, we have analyzed the macroscopic mechanical features of annular shear granular flow using probability statistic method. The predictions of the proposed discrete dynamical model and statistical method are quite agreeable with the existing experimental results. By considering the influences of initial packing fraction, shear rate and friction coefficient on the shear velocity profile, local packing fraction and coordinate number, we have investigate the mean flow features inside shear granular flows. We have also analyzed the distributing features of tangential velocity, radial velocity and spin angular velocity, and revealed some special particle motions inside different local regions. At last, using velocity fluctuations of microscopic particles, we investigate the self-diffusivity and transport processes inside shear granular flows. Such different kind's statistical results can provide an important theoretical basis for describing the dense shear granular flow accurately.Finally, the distributing and evolving features of contact force network in dense granular systems are investigated. The contact force network may provide a micro-mechanism for revealing the static, dynamic features in granular systems. So a statistical method under different force scales about the contact force network inside granular systems is presented, and it is also verified by comparing with the counterpart experiment results. We investigate the contact force distributions inside the static granular systems under the conditions of stochastic packing and confining pressure constraint. The influences of particle size distribution, packing fraction and constraint condition are also considered. Finally, we put our attention on the evolving features of contact force network inside a dynamical shear granular flow. From the numerical results we find a jamming transition and shear-induced anisotropy in dense shear granular flows.After all, the theoretical investigations of localized deformations under quasi-static loading, dynamical features under shearing, and distributing features of contact force network in dense granular systems must be important and useful for precise revealing and prediction macro mechanical features of granular systems. 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 for improving the research framework of mechanical system.