Research Highlight

The dynamics of rapid granular flows are well studied by the Institute of Mountain Hazards and Environment, Chinese Academy of Sciences

Pubdate:2017-07-14    From: ANDF    Views:

Understanding the characteristics and mechanics of granular flows along sloping channels is fundamental and vital for the study of different in situ geophysical flows. Dr. Gordon G. D. Zhou from the Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, used the discrete element method (DEM) and numerically modeled three-dimensional (3-D) dry granular flows to study the contact behavior of solid particles along sloping channels. 3-D velocity profiles along the flow height are determined and the corresponding shear rate is computed. The channel confinement effect on granular flows is also investigated. By capturing the flow height and utilizing the definition of the Savage number, the variation in flow regimes inside a granular body along a sloping channel is researched. The fluctuation of solid particles in the flow is investigated with the use of granular temperature, and is proven to be influenced by the Savage number. Analysis shows that the combination of granular temperature and the Savage number is a good way to identify the flow regimes of granular flows. Moreover, the limitation of the widely applied depth-averaged method based on the continuum mechanics for the numerical simulation of geophysical flows with rapid velocities and long run-out distances can be clearly understand.

For granular flows, the granular body may deform in a continuous fashion such that the solid particles remain in close contact. Previous research works have always used the frictional Coulomb-like continuum treatment for analyzing granular bodies. However, this approach is only applicable for quasi-static conditions and cannot capture the complicated granular contact behavior of solid particles inside a failing granular body. The research conducted by Dr. Gordon G. D. Zhou applies a revised Savage-Hutter equation to model granular flows moving down a confined, sloping channel. The Coulomb contact friction law is modified to consider the effect of the shear rate inside a granular body. This new method also considers the confinement effect of a sloping channel on granular flow mobility. The derived depth-averaged equations of motion bear a resemblance to nonlinear shallow-water wave equations. Results computed using the derived equations are compared with measurements from flume model tests and consistency is found between the two.

The research works are financial supported by the National Natural Science Foundation of China (grant no. 41201012) and the results have been published on the journal of Powder Technology (2013,239: 115-127) and Landslides (2014,11(3): 369-384)

 

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(a) Snapshots of the numerical simulated   granular avalanche and the evolution along the sloping channel;

(b) Computed   velocity distribution along the height and travel direction-Boundary layer   effect;

(c) The variation in shear rate along the travel direction for different travel times;

(d) Variation of granular temperature with flow height   in different flow regimes;

(e) Effect of solids segregation on the boundary   layer effect

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Comparison between experimental measurements and theoretical predictions of the granular flows