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Monday, November 30, 2009
10:00 AM - 11:00 AM
CNLS Conference Room (TA-3, Bldg 1690)


Multiscale modeling of granular flow: an application of the Voronoi tessellation

C. Rycroft
Dept. of Mathematics, LBNL

Dense granular flows occur in many practical and industrial situations but they are difficult to simulate due to an incomplete picture of the underlying physics. In the past decade, it has become possible to carry out large-scale three-dimensional simulations of these flows using the Discrete-Element Method (DEM), whereby individual grains are modeled according to Newton's laws. However these are computationally intensive, and even small problems can require days or weeks to run on a parallel computer.

The first half of this talk will discuss several techniques for rapidly simulating granular flows. By carrying out a mesoscopic analysis of large-scale DEM simulations, a model of dense granular rheology can be refined and tested. This can then be used as the basis of a multiscale simulation technique that runs much faster than DEM and would be appropriate for problems in real-time control and optimization.

The packing fraction is an important quantity in analyzing dense granular flow, and small changes can often be associated with a very different mechanical response. Accurately calculating the local packing fraction is challenging, but can be done using the Voronoi tessellation, and the second half of this talk will discuss a free software library, Voro++, that has been developed as part of this work. While other mature software libraries exist, Voro++ makes use of a direct construction in which each Voronoi cell is computed individually. This perspective is often useful in many physical applications that make use of cell-based statistics. The library is designed to be easily incorporated into other programs, and provides a flexible framework for handling walls and complex boundary conditions.

Host: Mikhail Shashkov