Boundary erosion by granular flow: Experiments and theory
Date Issued
2015
Date
2015
Author(s)
HUNG, Chi-Yao
Abstract
Granular avalanches flowing over loose beds evolve by gaining or losing grains through their basal boundary as stress and velocity change within the sheared layer. Kinetic energy dissipation results from internal dissipation and wall abrasion. By understanding the wall abrasion behavior, it is possible to build a bed rock erosion law. In this study both theory and experimental results are used to further understanding of granular avalanches and bed rock erosion. Experiments are performed in a vertical rotating drum which has a synthetic rock sample embedded into the wall and is used to simulate long period, steady bedrock erosion behavior. Through theory, we develop new depth-averaged equations assuming conservation of kinetic energy, mass and momentum to capture the flow process. For steady flows in rotating drums, we deduce two asymptotic regimes governed by a single dimensionless number, the Entrainment number, which controls flow geometry in the drum. Theoretical analysis is used to develop experimental design. Granular shear stress is scaled up by performing the experiments under enhanced gravity conditions in a geotechnical centrifuge. The velocity field are measured and compared with theoretical results. Through theory and the experiment observation, we develop an erosion model based on the kinetic energy exchanges. The proposed erosion model can be applied to both local erosion patterns and global erosion rates.
Subjects
kinetic energy
depth-averaged equation
scaling analysis
centrifuge experiments
Type
thesis
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