Quasi-gaussian velocity distribution of a vibrated granular bilayer system

We show by using a Discrete Element Method that a bilayer of vibrated granular bidisperse spheres exhibits the striking feature that the horizontal velocity distribution of the top layer particles has a quasi-Gaussian shape, whereas that of the bottom layer is far from Gaussian. We examine in detail the relevance of all physical parameters (acceleration of the bottom plate, mass ratio, layer coverage). Moreover, a microscopic analysis of the trajectories and the collision statistics reveal how the mechanism of randomization.