Application Of Discrete Element Method (DEM) To The Simulation Of Flow And Mixing Of Granular Materials

In contrast to physical experiments,the discrete element method(DEM)can readily reveal the details of granular flow at particle scale,and thus has been widely employed in fundamental research and engineering practice.However,most simulations based on DEM are restricted to small scale problems due to high computation cost.Based on previous work,a parallel simulation method and software for GPU(Graphics Processing Unit)-CPU(Central Processing Unit)heterogeneous computing of non-linear DEM models is optimized and extended to handle non-spherical particles,with which the flow and mixing of particles in horizontal drums and hoppers are simulated and analyzed systematically,which sheds light on the underlying mechanisms of granular flow.The research demonstrates that alternately arranged baffles in horizontal rotating drums can enhance radial scattering and axial streaming along the baffles,resulting in superior axial mixing efficiency.For the cases studied under optimal arrangements,the efficiency is almost 16 and 5 times of the corresponding drums without baffles and with full-length baffles,respectively.Moreover,this effect can be found in simulations with various particle properties,such as size,shape,density,and fiction coefficient.and drum dimensions,indicating its promising industrial application in more complicated mixers.It is also found that particle shape can influence the packing fraction and orientation distribution of the particles in rotating drums,which further affects the mixing efficiency.However,the shape effect is secondary to the density effect in the ranges simulated in this work.The joint effect of shape and density can be utilized to achieve better homogeneity by tuning the distribution of bidisperse mixtures at steady state.Moreover,by comparing with experimental data,the 3D force model for irregular particles developed in this work is found to be more accurate than traditional linear models in the simulation of hopper discharge.Based on this model,the simulation results indicate that the Beverloo equation can,in general,well predict the hopper discharging rate for different particle compositions.However,the equation will overestimate the flux under wide particle size distribution.The decrease in accuracy is ascribed to the intensifying of force chains near the hopper outlet which increases the flow resistance and the probability of arching.Finally,the important findings of this thesis are summarized,indicating that proper description of particle shapes and interactions can imporve the simulation accuracy effectively.The future work on DEM simulation for fundamental research and industrial applications is also prospected.