When the vertical vibration is applied to a U-tube filled with granular materials,the particles exhibit instability of directional migration of particles from one branch to another,which has an important influence on the transportation of granular materials.In order to investigate the dynamical behaviors and mechanisms of granular instability in the U-tube,the visualized simulation of dynamical process was carried out based on discrete element simulation.The effect of initial particle filling condition on the granular instability was analyzed,the evolution of velocity field during the development and saturation phases of granular instability was revealed,and the influence of wall friction on the granular instability was examined.The results showed that the granular instability was associated with the self-amplifying effect and the development phase of granular instability was affected by the initial filling conditions of particles.The surface level difference in the two branches of the U-tube in the final saturation phase was independent of the initial filling conditions of particles,which was in accordance with the experimental reports.In the development phase of granular instability,during the downward motion of the U-tube,the particles in the horizontal section expand towards the two vertical branches,transferring the particles to the branch with more particles but lower velocity of particles in the bottom.In the saturation phase,however,when the U-tube moved downward,the inertial effect in the branch with more particles resulted in higher particle velocities in the bottom,which inhibited the migration of the particles from the horizontal section into this vertical branch,causing the growth of granular surface level difference to cease.The granular instability did not occur when the sliding friction coefficient of the tube wall was too small or too large.
关键词
颗粒物料/不稳定性/数值模拟/U形管/竖直振动/离散元方法
Key words
granular materials/instability/numerical simulation/U-tube/vertical vibration/discrete element method
维普
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