Title: Traveling Waves in Axial Segregation: The Dynamics of Subsurface Core
Speaker: Stephen Morris
Speaker Info: University of Toronto
Brief Description:
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Abstract:
Axial segregation is a striking phenomenon which is often observed when granular materials of different sizes are rotated in a horizontal cylindrical drum; the grains separate according to their size into bands along the axis of the drum. Recently, a transient travelling wave state has been found to occur prior to axial segregation in a mixture of salt and sand grains. The existence of complex wave-like dynamics leading up to segregation cannot be explained by the simple reverse diffusion model of Savage, or its later elaborations. A new model of the segregation process has been proposed that describes both wave dynamics and axial segregation. The model uses two local variables, the concentration difference of large to small grains and the dynamic angle of repose, the angle which the flowing surface of grains forms. The model takes the form of two coupled nonlinear diffusion equations for the radially averaged quantities and can be plausibly derived from a more primitive three-dimensional transport model. This model predicts that these two axial fields are 90 degrees out of phase during the transient travelling wave state, and are in phase for the axially segregated state.Date: Friday, May 23, 2003