Granular instability in a vibrated U tube

TL;DR

This paper investigates the collective motion of grains in a vibrated U tube, identifying two growth behaviors influenced by grain size and air presence, supported by a simple model matching experimental data.

Contribution

It introduces a simple quantitative model that captures the key features of granular instability in a vibrated U tube, highlighting the roles of grain size and air.

Findings

Height difference grows over time at low frequencies.

Two growth types: exponential divergence and saturation.

Air presence affects the growth behavior.

Abstract

We study experimentally the collective motion of grains inside a U shaped tube undergoing vertical oscillations, and we develop a very simple quantitative model that captures relevant features of the observed behaviour. The height difference between the granular columns grows with time when the system is shaken at sufficiently low frequencies. The system exhibits two types of growth: exponentially divergent (type I) and exponentially saturating (type II), depending on the size of the grains. The type I growth can be quenched by removing the air whereas the type II behavior can occur in the absence of air. There is a good agreement between the model proposed and our experimental results.