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Multiscale Modelling of Granular Flows

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Geophysical hazards, such as avalanches, debris flows and submarine landslides, involve rapid mass movement of granular solids, water and air as a single-phase system. The momentum transfer between the discrete and continuous phases significantly affects the dynamics of the flow. The dynamics of a granular flow involve at least three distinct scales:the microscopic scale, which is characterised by contact between particles, the meso-scale, which represents micro-structural effects such as particle rearrangement, and the macroscopic scale. This study aims to understand the ability of continuum models in capturing the micro-mechanism of granular flow dynamics. The initiation and propagation of granular flows depend mainly on the slope, density, and quantity of the material destabilised. Material Point Method (MPM), a hybrid Lagrangian and Eulerian approach is used to describe the continuum behaviour of granular flow dynamics, while the micro-mechanics is captured using Discrete Element Method (DEM) with tangential contact force model.

Most macroscopic models are able to capture simple mechanical behaviours, however the complex physical mechanisms that occur at the grain scale, such as hydrodynamic instabilities, the formation of clusters, collapse, and transport, have largely been ignored. In order to describe the mechanism of saturated and/or immersed granular flows, it is important to consider both the dynamics of the solid phase and the role of the ambient fluid. Two-dimensional sub-grain scale numerical simulations are performed to understand the local rheology of a dense granular flows in fluid. Discrete Element Method is coupled with the Lattice Boltzmann Method (LBM) for fluid-grain interactions, to understand the evolution of immersed granular flows. A parametric analysis is performed to assess the influence of the grain sample characteristics (initial configuration, permeability, slope of inclined plane) on the evolution of flow and run-out distances. The effect of hydrodynamic forces and hydroplaning on the run-out evolution is analysed by comparing the mechanism of energy dissipation and flow evolution in dry and immersed granular flows

This talk is part of the Engineering Department Geotechnical Research Seminars series.

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