Spring 2016

Seminars are held on Mondays from 2:30 - 3:30PM in Cullimore Hall, Room 611, unless noted otherwise. For questions about the seminar schedule, please contact David Shirokoff.

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Date: February 29, 2016

Speaker: Abe Clark
Department of Mechanical Engineering & Materials Science,
Yale University

Title: "A Phase Diagram for Fluid-Driven Sediment Transport"

Abstract:

Fluid flowing laterally over a granular bed exerts a shear stress on the grains, and grains can be transported if the flow is sufficiently fast. This process shapes much of the natural world, and it has been studied for decades. However, the nature of the boundary between systems with and without grain motion is still not clearly understood, since this system involves nontrivial coupling between several complex physical processes: generally turbulent fluid flow above the bed, Darcy flow inside the bed, and the yield stress of granular materials of varying shape and size. Here, I will describe a continuing line of research, where we seek to identify the basic physical mechanisms that govern sediment transport (and related problems) by performing numerical simulations of simplified systems with only the most crucial elements. We start by including only gravity, frictionless grain-grain interactions, and a purely horizontal viscous fluid flow. By varying the fluid flow rate and the effective viscosity, we find behavior that is qualitatively consistent with a large collection of experimental data known as the Shields curve. Thus, our results suggest that the main features of this curve result from a competition between grain inertia and viscous damping. We find this phase diagram to be qualitatively insensitive to secondary effects, such as friction, irregular grain shape, and restitution losses.