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Exact solution for granular flows
Author(s) -
Faccai Gloria,
Mangeney Anne
Publication year - 2013
Publication title -
international journal for numerical and analytical methods in geomechanics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.419
H-Index - 91
eISSN - 1096-9853
pISSN - 0363-9061
DOI - 10.1002/nag.2124
Subject(s) - riemann problem , granular material , riemann hypothesis , exact solutions in general relativity , nonlinear system , mathematics , shallow water equations , riemann solver , type (biology) , mechanics , mathematical analysis , classical mechanics , physics , geotechnical engineering , finite volume method , geology , paleontology , quantum mechanics
SUMMARY In this paper, we present the exact solution of the Riemann problem for the nonlinear one‐dimensional so‐called shallow‐water or Saint‐Venant equations with friction proposed by SAVAGE and HUTTER to describe debris avalanches. This model is based on the depth‐averaged thin layer approximation of granular flows over sloping beds and takes into account a Coulomb type friction law with a constant friction coefficient. A particular configuration of the Riemann problem corresponds to a dam of infinite length in one direction from which granular material is released from rest at a given time over an inclined rigid or erodible bed. We solve analytically and numerically the depth‐averaged long‐wave equations derived in a topography‐linked coordinate system for all the possible Riemann problems. The detailed mathematical proof of the derivation of the analytical solutions and the analysis of their structure and properties is intended, first of all, for geophysicists, mathematicians, and physicists because of the possible extension of this study to more complex problems (geometries, friction laws, …). The numerical solution of the first‐order finite‐volume method based on a Godunov‐type scheme is compared with the proposed exact Riemann problem solution. This solution is used to solve the dam‐break problem and analyze the influence of the thickness of the erodible bed on the speed of the granular front. Comparison with existing experimental results shows that, for an erodible bed, the equations lack fundamental physical significance to reproduce the observed dynamics of erosive granular flows. Copyright © 2012 John Wiley & Sons, Ltd.