A numerical study of the segregation phenomenon in granular motion

摘要

Over the past decade, many studies have been carried out to investigate one of the unique phenomena in granular materials: the vibration-induced segregation in granular mixture, i.e., under vertical vibration, larger granules (sometimes referred to as intruders) rise to the top even without density difference with other granules. To date, the mechanisms behind this phenomenon and the factors affecting the segregation are not yet completely understood. In this study, the discrete element method (DEM) is used for the numerical analysis of granular segregation in a vertically vibrating container. The rise time of an intruder inside the granular mixture is systematically investigated as a function of the granular size, density, depth, and the vibrating frequency and amplitude. Our study shows that the segregation phenomenon is caused by a variety of mechanisms within different vibration regimes. Under weak vibration, the segregation is mainly 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, buoyancy or sinkage of granules prevails and segregation may be suppressed.