Shear Flows of Dense Granular Assemblies

The Chemical and Biological Engineering department and the Wanger Institute for Sustainable Energy Research (WISER) will be hosting a seminar featuring Professor of Chemical and Biological Engineering at Princeton University, Dr. Sankaran Sundaresan. The topic of the seminar will be Shear Flows of Dense Granular Assemblies.

Abstract

Dense assemblies of granular materials in motion, encountered in industries and in nature, manifest multiple flow regimes. Most flows of interest involve a large number of particles, rendering any effort to follow the motion of all the individual particles impractical. Continuum analysis for granular flows require good rheological models; but, for dense granular assemblies, reliable models that are linked to particle-level properties are often not available. As a result, quantitative prediction of the flow characteristics of dense assemblies of granular materials through solution of continuum models remains a challenge. The research described in this presentation is aimed at constructing rheological models in terms of particle-level properties.

Towards this end, the discrete element method (DEM) is used to simulate the motion of individual particles in deforming assemblies; the stress and kinematics information at the continuum level are then obtained through statistical averaging. The simulations also afford detailed information about internal variables such as the fabric tensor and the coordination number of particles involved in force chains, which characterize the evolution of the microstructure of the assembly. These results are then analyzed to first identify the internal variables that are natural candidates to describe the stress evolution and then seek quantitative relations that form the basis for continuum rheological models.

The presentation will first focus on flow regimes observed in shear flows of nearly homogeneous assemblies of uniformly sized, spherical, non-cohesive particles. A dynamic plasticity model for slow quasi-static flows and a modified kinetic theory for rapid inertial flows, inspired by the simulation results, will then be outlined.

The effect of cohesive interaction between particles on the regimes observed in homogeneous shear flows of dense assemblies will then be highlighted.

Finally, wall boundary conditions deduced from the results of DEM simulations of bounded shear flows will be discussed.