Dynamics of rotating spirals in agitated wet granular matter

TL;DR

This study experimentally investigates the pattern formation of rotating spirals in vertically agitated wet granular matter, revealing how cohesion influences the emergence and dynamics of these patterns.

Contribution

It provides the first detailed analysis of rotating spiral patterns in wet granular matter, highlighting the role of cohesion and phase kinks in pattern formation.

Findings

Rotating spirals with three arms are the dominant pattern.

The rotation frequency increases linearly with vibration acceleration.

A finite threshold vibration acceleration is required for spiral rotation.

Abstract

Pattern formation of a thin layer of vertically agitated wet granular matter is investigated experimentally. Due to the strong cohesion arising from the capillary bridges formed between adjacent particles, agitated wet granular matter exhibits a different scenario compared with cohesionless dry particles. Rotating spirals with three arms, which correspond to the kinks between regions with different colliding phases with the vibrating plate, have been found to be the dominating pattern. From both top view snapshots and laser profilometry methods, the rotation frequency of the spiral arms is characterized with image processing procedures. Both methods reveal that there exists a finite rotation frequency $\nu_{\rm r}$ at a threshold vibration acceleration, above which $\nu_{\rm r}$ increases linearly with the peak vibration acceleration with a slope strongly dependent on the vibration frequency.