Simulation Of Particle Flow In A Hopper By GPU Based DEM

Hoppers have been widely used in the industry for transportation of particles due to their relatively simple structure and low cost.A main challenge with the use of hoppers is the presence of unstable discharge.This not only reduces the transporting efficiency,but also has significant effects on operation stability and safety during the particle transportation.Despite many attentions have been paid to solve this problem,the nature of the unstable discharge in hoppers has not been well understood.In this dissertation,we started from the particle flow in a hopper via the discrete element(DEM)method with the aim to understand the unstable discharge.Based on the detailed hopper flow regions,the nature of the unstable discharge in a hopper was revealed.Controlling the height index in the hopper was proposed to avoid the unstable operation,and a correlation constrain equations was established to calculate the Critical stable height.Furthermore,an equivalent gravity model was developed to simulate the particle discharge in a hopper under pressure.Understanding the characteristics of particle flow in hoppers is crucial to reveal the nature of discharge stability.However,the material heights in the previous studies were not high enough to eliminate the influences of the hopper outlet,and hence could not clarify the mechanism of the particle flow in the transition flow region.In this study,the material height was selected to be high enough to investigate the mechanism of the transition flow region via the GPU-based discrete element method The results showed that when the hopper flow stability changes,a key transformation zone occurs in the transition flow region.In the presence of the unstable flow in the key transformation zone,particles in the zone start to accelerate and then to flow through the outlet.During this process,the velocities of particles through the outlet have no obvious change and the hopper discharge can be still stable.This indicates that the nature of the unstable hopper discharge is due to the unstable particle flow,and the variation of the discharge results from the variation of particle flow.These results are the foundation for establishment of the constraint equations for stable hopper operation.The material height that the viodage of the key transportation zone increases is defined as the Critical stable height.To avoid unstable hoper flow,the material height should be higher than the Critical stable height.With further investigating the effect of the particle properties(e.g.particle density and internal friction coefficient of particles)and the outlet size on the Critical stable height,a correlation constraint equations was proposed.These equations provide guidelines for the design of stable hopper operation.The hopper under pressure was usually simulated via the complicated CFD-DEM method.To simplify the simulation process,with combination of the particulate media mechanics and the DEM theory,an equivalent gravity model was developed to simulate the hopper under pressure.The gravity in the DEM model was modified by the particulate media mechanics,and thus the simulation process can be considerably simplified without coupling with other software.This is favorable for further investigation of hoppers in the future.