Ripples in Tapped or Blown Powder

TL;DR

This study investigates the formation of stable ripple patterns on granular powder surfaces caused by repeated shocks, revealing a proportional relationship between pattern wavelength and shock amplitude, supported by a semi-quantitative model.

Contribution

It introduces a new experimental observation of ripple formation on granular surfaces and develops a semi-quantitative model explaining the pattern's characteristics.

Findings

Ripple wavelength is proportional to shock amplitude.

Patterns become stable after a few shocks.

Model fits experimental data well.

Abstract

We observe ripples forming on the surface of a granular powder in a container submitted from below to a series of brief and distinct shocks. After a few taps, the pattern turns out to be stable against any further shock of the same amplitude. We find experimentally that the characteristic wavelength of the pattern is proportional to the amplitude of the shocks. Starting from consideration involving Darcy's law for air flow through the porous granulate and avalanche properties, we build up a semi-quantitative model which fits satisfactorily the set of experimental observations as well as a couple of additional experiments.