Gravity-driven dry granular slow flows down an inclined moving plane: a comparative study between two concepts of the evolution of porosity |
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Authors: | Chung Fang |
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Institution: | (1) Department of Civil Engineering, National Cheng Kung University, No.1, University Road, Tainan City, 701, Taiwan |
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Abstract: | Two concepts in modeling the effects of the evolution of porosity in dry granular flows are investigated to illuminate their
performance and limitations. To this end, the thermodynamic analysis, based on the Müller-Liu entropy principle, and the quasi-linear
theory, are employed to deduce the ultimate constitutive models and the restrictions on their thermodynamic consistencies.
The models are employed to study an isothermal dry granular slow flow down an inclined moving plane, of which the results
are compared with the experimental outcomes. Results show that, while the two models deliver appropriate equilibrium expressions
of the Cauchy stress tensor for compressible grains, the model in which the evolution of porosity is treated kinematically
yields a spherical stress tensor for incompressible grains. Only the model with a dynamic evolution of porosity can give rise
to a non-spherical stress tensor at equilibrium. Moreover, whilst the former model can better capture the characteristics
of flows with slow to moderate speeds, the latter model is more able to describe the features of very rapid flows like avalanches.
The present study illustrates the essential difference between the two concepts in modeling the effects of the evolution of
porosity, and can be extended for further studies on other microstructural effects in granular flows. |
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