Propagating front in an excited granular layer

TL;DR

This study investigates the stability and transition dynamics of a vibrated granular layer, revealing a propagating front phenomenon triggered by external perturbations and modeled through particle attractors and collision effects.

Contribution

It introduces a model based on a single vibrated particle with multiple attractors and demonstrates how collision rates influence state transitions in granular layers.

Findings

Propagation front velocity depends on acceleration.

High collision rates prevent trapping in nonmoving states.

Transition from amorphous to gaseous state is subcritical.

Abstract

A partial monolayer of ~ 20000 uniform spherical steel beads, vibrated vertically on a flat plate, shows remarkable ordering transitions and cooperative behavior just below 1g maximum acceleration. We study the stability of a quiescent disordered or ``amorphous'' state formed when the acceleration is switched off in the excited ``gaseous'' state. The transition from the amorphous state back to the gaseous state upon increasing the plate's acceleration is generally subcritical: An external perturbation applied to one bead initiates a propagating front that produces a rapid transition. We measure the front velocity as a function of the applied acceleration. This phenomenon is explained by a model based on a single vibrated particle with multiple attractors that is perturbed by collisions. A simulation shows that a sufficiently high rate of interparticle collisions can prevent trapping in the attractor corresponding to the nonmoving ground state.