Metastability of a granular surface in a spinning bucket

TL;DR

This paper investigates the metastability of granular surfaces in spinning buckets using a continuum model, revealing how system size influences the stability and the mechanisms leading to surface destabilization.

Contribution

It demonstrates how a continuum model can reproduce experimental observations of metastable regions and elucidates the nonlinear instability mechanisms involved.

Findings

Metastable regions depend on system size and vanish as size increases.

Nonlinear instability causes surface destabilization in large systems.

Linear instability is relevant for smaller systems.

Abstract

The surface shape of a spinning bucket of granular material is studied using a continuum model of surface flow developed by Bouchaud et al. and Mehta et al. An experimentally observed central subcritical region is reproduced by the model. The subcritical region occurs when a metastable surface becomes unstable via a nonlinear instability mechanism. The nonlinear instability mechanism destabilizes the surface in large systems while a linear instability mechanism is relevant for smaller systems. The range of angles in which the granular surface is metastable vanishes with increasing system size.