Convective and diffusive motions of granular materials in a vibrated bed

In this study, Discrete Element Method (DEM) is employed to simulate the motion of granular materials in a three-dimensional vibrated bed. With frictional sidewalls, the convection flow is a very important phenomenon in the vibrated granular bed. The influence of vibrating conditions, including vibration acceleration and frequency, on the formation of symmetric convection flow is investigated in this work. In order to characterize the convective flow and the diffusive motion of granular materials, the dimensionless convection flow rate, J^conv, and the vertical self-diffusion coefficient, D ^yy are defined, respectively. The Peclet number, Pe, is employed to characterize the ratio of the convective flow to the diffusive motion in vertical direction. The role of Pe in the formation of symmetric convection flow is discussed in detail.