Title:	From discrete particles to continuum fields
Date:	11:00 AM Wednesday, 24th July 2013
Venue:	EN202, Engineering Building
Speaker:	Dr Thomas Weinhart, University of Twente, Netherlands
Abstract:	Gravity-driven free surface flows are common in both geophysical environments and industry, occurring across many orders of magnitude. Common examples range from rock slides, particle flow into blast furnaces for iron-ore melting, to sand flowing in an hour-glass. Discrete particle simulations are a powerful tool to investigate granular systems, allowing the simulation of several million particles. However, full DEM simulations of real geophysical flow will remain unreachable, given the numbers involved. Continuum models are more practical to simulate these flows, and are based on closure relations, reducing the properties of many discrete particles to a few continuum variables. We show how to obtain such closure relations from discrete particle simulations. Therefore, we present a novel method to determine the macroscopic stress tensor of discrete mechanical systems that is applicable near boundaries and interfaces [1]. It is derived by coarse-graining the mass and momentum balance equations and thus satisfies them exactly. Boundary interaction forces are taken into account in a selfconsistent way and thus allow the construction of continuous stress and interaction force fields, avoiding many problems other methods have near boundaries. The resolution and shape of the coarse-graining function used in the formulation can be chosen freely. The method does not require temporal averaging and thus can be used to investigate rapid, time-dependent flows as well as static and steady situations. To illustrate the strengths of this new stress formulation, we consider the stress near a highly rough wall and show how to obtain the exact shear stress (friction) at the boundary. [1] Weinhart, T., Thornton, A.R., Luding, S., Bokhove, O., From discrete particles to continuum fields near a boundary, Granular Matter 14(2), 289-294 (2012).
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