Ben Alessio

“Complex granular rheologies from microfluctuations”

Advised by Prof. Ching-Yao Lai

Abstract: Connecting small-scale fluctuations to continuum granular flow descriptions remains an open challenge. Motivated by geophysical observations of nonlocal granular flows of ice mélange, the world's largest granular material, we develop a discrete-element model for granular flow. The key barrier to predictions of nonlocal granular flows is the fluctuating energy balance law which would relate the mean shear field and state parameters to the so-called granular temperature, a measure of velocity fluctuations. Using a data-driven approach we predict the granular temperature field of an idealized model for ice mélange flow to demonstrate the resulting viscosity structure and flow dynamics; furthermore we infer the granular rheology and devise a continuum model for the discrete-element simulation. Some mysterious flow properties of ice mélange include multiscale contributions to the viscosity, transient wall interactions or stick-slip behavior, and streamwise expansion. Using our idealized model, we demonstrate critical transitions in the rheology which can activate these effects. Capitalizing on recent developments in liquid-state theory, we investigate, toward a complete granular rheology, how these macroscopic behaviors can be related to grain-scale fluctuations. Finally we present a universal drag force law for granular materials across a wide range of Reynolds numbers.