Forcing and Velocity Correlations in a Vibrated Granular Monolayer

TL;DR

This study explores how different forcing methods affect the velocity correlations and distribution in a vibrated granular monolayer, revealing negative correlations with flat plates and positive with rough plates, supported by experiments and simulations.

Contribution

It introduces a mechanism explaining velocity anti-correlations in vibrated granular layers and compares effects of flat versus rough plate forcing.

Findings

Negative velocity correlations with flat plates

Positive velocity correlations with rough plates

Velocity distribution broadens at higher densities

Abstract

The role of forcing on the dynamics of a vertically shaken granular monolayer is investigated. Using a flat plate, surprising negative velocity correlations are measured. A mechanism for this anti-correlation is proposed with support from both experimental results and molecular dynamics simulations. Using a rough plate, velocity correlations are positive, and the velocity distribution evolves from a gaussian at very low densities to a broader distribution at high densities. These results are interpreted as a balance between stochastic forcing, interparticle collisions, and friction with the plate.