The dynamics of thin vibrated granular layers

TL;DR

This paper investigates the complex behaviors of vibrated granular layers through experiments and simulations, revealing various phase states, velocity distributions, and correlations influenced by system parameters and energy dissipation.

Contribution

It provides new experimental observations of solid phases and velocity correlations in vibrated granular media, expanding understanding of their phase behavior and dynamics.

Findings

Identification of multiple solid phases at high densities and amplitudes

Velocity distributions range from Maxwellian to non-Maxwellian

Increased inelasticity enhances particle self-diffusion

Abstract

We describe a series of experiments and computer simulations on vibrated granular media in a geometry chosen to eliminate gravitationally induced settling. The system consists of a collection of identical spherical particles on a horizontal plate vibrating vertically, with or without a confining lid. Previously reported results are reviewed, including the observation of homogeneous, disordered liquid-like states, an instability to a `collapse' of motionless spheres on a perfect hexagonal lattice, and a fluctuating, hexagonally ordered state. In the presence of a confining lid we see a variety of solid phases at high densities and relatively high vibration amplitudes, several of which are reported for the first time in this article. The phase behavior of the system is closely related to that observed in confined hard-sphere colloidal suspensions in equilibrium, but with modifications due to the effects of the forcing and dissipation. We also review measurements of velocity distributions, which range from Maxwellian to strongly non-Maxwellian depending on the experimental parameter values. We describe measurements of spatial velocity correlations that show a clear dependence on the mechanism of energy injection. We also report new measurements of the velocity autocorrelation function in the granular layer and show that increased inelasticity leads to enhanced particle self-diffusion.