A Microscopic Description of the Granular Fluidity Field in Nonlocal Flow Modeling

TL;DR

This paper identifies the physical basis of the granular fluidity field in nonlocal flow modeling as a kinematic variable related to velocity fluctuations and packing fraction, validated through simulations and theoretical analysis.

Contribution

It reveals the microscopic origin of the granular fluidity field, linking it to velocity fluctuations and packing fraction, and verifies this with simulations and theoretical insights.

Findings

Granular fluidity is a kinematic variable.

Simulation results confirm the microscopic formula.

Theoretical explanations support the fluidity's form.

Abstract

A recent granular rheology based on an implicit `granular fluidity' field has been shown to quantitatively predict many nonlocal phenomena. However, the physical nature of the field has not been identified. Here, the granular fluidity is found to be a kinematic variable given by the velocity fluctuation and packing fraction. This is verified with many discrete element simulations, which show the operational fluidity definition, solutions of the fluidity model, and the proposed microscopic formula all agree. Kinetic theoretical and Eyring-like explanations shed insight into the obtained form.