Analysis of Segregation Phenomenon in Granular Motion

Over the past decade, many studies have been carried out to investigate one of the unique phenomena in granular materials: vibration-induced segregation in granular mixture, i.e., under vertical vibration, larger granules rise to the top even without density difference with other granules. However, the mechanisms behind this phenomenon are not yet completely understood. In this study, the discrete element method (DEM) is used for the numerical analysis of the granular segregation in a vertically vibrating container. We systematically investigate the rising time of an intruder inside the granular mixture as a function of the granular size, density, depth, and the vibrating frequency and amplitude. Our studies show that the segregation phenomenon is caused by a variety of mechanisms within different vibration regimes. Under weak vibration, segregation is driven by the geometrical effect and inertia. Under moderate vibration, segregation can be enhanced dramatically with the occurrence of convection. Under strong vibration where the granular material becomes fluidized, the buoyancy or sinkage of granules prevails and segregation may be suppressed.