Noise, coherent fluctuations, and the onset of order in an oscillated granular fluid

TL;DR

This study investigates fluctuations and the emergence of order in a vertically oscillated granular layer, revealing that granular noise significantly exceeds thermal noise and influences the onset of ordered waves.

Contribution

It demonstrates that granular noise is much larger than thermal noise and affects the transition to order, aligning with Swift-Hohenberg theory but with notable differences.

Findings

Granular noise is four orders of magnitude larger than thermal noise.

Disordered waves with a characteristic length scale emerge near the onset.

The shift in the onset of order matches Swift-Hohenberg theory predictions.

Abstract

We study fluctuations in a vertically oscillated layer of grains below the critical acceleration for the onset of ordered standing waves. As onset is approached, transient disordered waves with a characteristic length scale emerge and increase in power and coherence. The scaling behavior and the shift in the onset of order agrees with the Swift-Hohenberg theory for convection in fluids. However, the noise in the granular system is four orders of magnitude larger than the thermal noise in a convecting fluid, making the effect of granular noise observable even 20% below the onset of long range order.