Onset of fluidization in vertically shaken granular material

TL;DR

This paper investigates the onset of fluidization in vertically shaken granular materials, combining theoretical analysis and simulations to challenge the existence of a single threshold for fluidization effects.

Contribution

It proposes a modified criterion for fluidization onset that aligns with the critical Froude number at low frequencies, refuting the idea of a universal threshold.

Findings

No single threshold for fluidization effects exists.

A modified criterion matches the critical Froude number at low frequencies.

Theoretical and simulation results support the new criterion.

Abstract

When granular material is shaken vertically one observes convection, surface fluidization, spontaneous heap formation and other effects. There is a controversial discussion in literature whether there exists a threshold for the Froude number $\Gamma=A_0\omega_0^2/g$ below which these effects cannot be observed anymore. By means of theoretical analysis and computer simulation we find that there is no such single threshold. Instead we propose a modified criterion which coincides with critical Froude number $\Gamma_c=1$ for small driving frequency $\omega_0$.