Continuum simulation of granular flows using the lattice Boltzmann method

Granular avalanches pose significant threats to human life and economic development in mountainous regions. Rheological models for granular avalanches have been proposed based on steady granular flows, such as simple shear. There is still a lack of efficient and accurate numerical models for the prediction of granular avalanche behaviors in an unsteady state. In this project, the discrete element method (DEM) is adopted to simulate granular column collapse, which is regarded as a common model case for unsteady geophysical flows. First, the discrete data from DEM simulations, including particle velocities and inter-particle forces, are converted to continuous flow fields with high accuracy using the coarse-graining technique. A rheological model for unsteady granular column collapses will be constructed based on the local averaged flow fields. Then, the lattice Boltzmann method (LBM), with a dynamic free-surface based on the volume of fluid method, will be adopted to simulate granular column collapses. In LBM, an adaptive relaxation time depending on the local shear rate will be used such that the flow behavior follows the constitutive relation for unsteady granular avalanches. By comparing the numerical results from discrete element and lattice Boltzmann simulations, in terms of the deposit morphology and the internal flow fields, the constitutive model for unsteady granular avalanches can be verified. Last but not least, the graphic processor unit will be used to accelerate the lattice Boltzmann calculations based on compute unified device architecture. The current project will establish an efficient and accurate numerical model for unsteady granular avalanches that supports heterogeneous parallel computing, which has the potential to guide the design of hazard mitigation measures.