The dynamics of thin vibrated granular layers

Abstract

We describe a series of experiments and computer simulations on vibrated granularmedia in a geometry chosen to eliminate gravitationally induced settling. Thesystem consists of a collection of identical spherical particles on a horizontal platevibrating vertically, with or without a confining lid. Previously reported results arereviewed, including the observation of homogeneous, disordered liquid-like states, aninstability to a ‘collapse’ of motionless spheres on a perfect hexagonal lattice,and a fluctuating, hexagonally ordered state. In the presence of a confining lidwe see a variety of solid phases at high densities and relatively high vibrationamplitudes, several of which are reported for the first time in this article. Thephase behaviour of the system is closely related to that observed in confinedhard-sphere colloidal suspensions in equilibrium, but with modifications due to theeffects of the forcing and dissipation. We also review measurements of velocitydistributions, which range from Maxwellian to strongly non-Maxwellian depending on theexperimental parameter values. We describe measurements of spatial velocity correlationsthat show a clear dependence on the mechanism of energy injection. We alsoreport new measurements of the velocity autocorrelation function in the granularlayer and show that increased inelasticity leads to enhanced particle self-diffusion.