Particle size segregation, shock waves and pattern formation in granular avalanches


J.M.N.T. Gray (University of Manchester)


Hazardous natural flows such as snow avalanches, debris-flows, lahars and pyroclastic flows are part of a much wider class of granular avalanches, that frequently occur in industrial processes and in our kitchens! Granular avalanches are very efficient at sorting particles by size, with the larger ones rising towards the free surface and the smaller ones percolating down to the base, to create inversely-graded layers. When these are brought to rest by the propagation of shock waves, or by basal deposition, many beautiful and complex patterns are formed in the deposits. This talk will review some of the recent advances that have been made in modelling particle size segregation and show how these theories can be incorporated into existing avalanche models. In particular, the segregation of particles with different material properties has important segregation mobility feedback effects on the bulk flow, which are responsible for the spontaneous formation of lateral levees, the selection of the petal wavelength in rotating drums and stratification patterns in a granular heap. This talk will show how such fully coupled models can be constructed.

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