The influence of filling ratio and container geometry on granular convection and the dynamical mechanisms of three unconventional convection patterns in a vibrated granular bed

Abstract

Granular convection typically refers to the cyclic flow phenomenon observed in dense granular systems subjected to vertical sinusoidal vibration, where discrete particles descend along the container walls and rise in the center of the container. This process plays a crucial role in the overall transport and mixing of particles and has important applications in vibration processing techniques, such as Resonant Acoustic Mixing (RAM). However, current research on the changes in convection flow patterns and underlying mechanisms under conditions of low aspect ratio containers (< 1:4), high filling ratios of granular systems (nearly full), and inclined container walls is limited. Under these atypical conditions, the forms of granular convection and the associated dynamical mechanisms remain unclear. This study focuses on the effects of these three parameters on granular convection, employing the Discrete Element Method (DEM) to simulate and analyze granular convection phenomena in a 3D container. The results indicate that a multilayer convection pattern emerges under low aspect ratio conditions, a centrosymmetric convection pattern appears under nearly full-filling conditions, and a reverse convection pattern develops under inclined wall conditions. Furthermore, we analyze and explain the dynamical mechanisms behind these three unconventional convection patterns: the multilayer convection pattern arises from the longer time required for vibrations to propagate to higher positions in low aspect ratio conditions; the centrosymmetric convection pattern is caused by the top of the container becoming a new source of excitation; the dynamical mechanism of the reverse convection pattern not only involves shear forces along the walls but also considers the normal support force from the walls as a new driving force for convection. These findings are expected to provide theoretical support for granular convection control.