A Vibrated Compacting Granular System: A DEM Light Scattering Comparison

TL;DR

This study uses DEM simulations to analyze vibrated granular particles, revealing that rotational dynamics significantly influence experimental measurements and that the system becomes dynamically constrained before reaching close packing.

Contribution

It demonstrates that rotational particle motion dominates DWS signals and introduces a new perspective on measuring particle dynamics in vibrated granular systems.

Findings

MSD from simulations exceeds experimental DWS measurements

Rotational MSD is comparable to DWS signals, indicating rotational dominance

System becomes dynamically constrained before reaching random close packing

Abstract

We perform Discrete Element Method (DEM) simulations of granular particles (polystyrene spheres) vibrated inside a cubic container. The study investigates the evolution of the packing fraction with and without rotational friction at different shaking amplitudes. The mean-squared displacement (MSD) is used to analyze the particles' diffusive, subdiffusive, and superdiffusive behavior. By monitoring both the dynamics and density evolution, one can observe the system's glassification. The comparison with experiments shows that the MSDs from the simulations are significantly higher than the MSDs measured by Diffusing Wave Spectroscopy (DWS) \cite{kunzner2025dynamics}. Following our finding that the rotational MSD is of the same order of magnitude as the MSD measured in DWS experiments, we propose that the experimental signal is not dominated by translational motion but rather by rotational particle dynamics. This provides access to a relevant particle property that has previously been difficult to measure directly. Finally, we conclude that the system reaches a dynamically constrained state well before random close packing, with particle displacements already below the Lindemann length.