Collective drifts in vibrated granular packings: the interplay of friction and structure

TL;DR

This study investigates how structural disorder and friction in vibrated granular materials lead to collective drift, revealing a nonlinear ratchet mechanism that explains persistent rotations and anomalous diffusion.

Contribution

It introduces a nonlinear ratchet model with stick-slips to explain collective drift caused by symmetry breaking and friction in vibrated granular packings.

Findings

Emergence of coordinated translation in granular packings under weak shaking

The nonlinear ratchet model reproduces observed collective motions

Structural disorder and friction interplay cause persistent drift phenomena

Abstract

We simulate vertically shaken dense granular packings with horizontal periodic boundary conditions. A coordinated translating motion of the whole medium emerges when the horizontal symmetry is broken by disorder or defects in the packing and the shaking is weak enough to conserve the structure. We argue that such a drift originates in the interplay between structural symmetry breaking and frictional forces transmitted by the vibrating plate. A non-linear ratchet model with stick-slips reproduces many faces of the phenomenon. The collective motion discussed here underlies phenomena observed recently with vibrofluidized granular materials, such as persistent rotations and anomalous diffusion.