Avalanche statistics and time-resolved grain dynamics for a driven heap

TL;DR

This study investigates the dynamics of avalanches in a granular heap, revealing how grain flow and fluctuation speeds vary during events and how these relate to avalanche size and timing, with implications for understanding granular flow behavior.

Contribution

The paper introduces time-resolved measurements of grain and flow speeds during avalanches, highlighting the relationship between fluctuation and average speeds and the transition to continuous flow at high addition rates.

Findings

Fluctuation speed is about one-tenth of average flow speed during avalanches.

Event durations are peaked, indicating characteristic timescales.

At high addition rates, the speed relationship shifts to dv proportional to sqrt[v].

Abstract

We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two dimensional heap. To characterize the time-dependent average avalanche flow speed v(t), we image the top free surface. To characterize the grain fluctuation speed dv(t), we use Speckle-Visibility Spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow speed, and that these speeds are largest near the beginning of an event. We also find that the distribution of event durations is peaked, and that event sizes are correlated with the time interval since the end of the previous event. At high rates of grain addition, where successive avalanches merge into smooth continuous flow, the relationship between average and fluctuation speeds changes to dv Sqrt[v].