From Micro to Large Scale Models: Porosity Homogenization Schemes for DEM Simulations

Abstract

There are many applications where require in-depth understanding of the underlying dynamics of the fluid-particle interaction and predict phenomena which are detrimental for human lives. For example, internal erosion in dams and beneath flood embankments can be occurred due to the variation in the total head of the fluid causing particle motion, slope instabilities can be triggered due to fluid flows and liquefaction can be caused from an increase in the fluid pressure. All these failures are triggered by actions at a micro-scale, constituting the coupled CFD-DEM models the optimum numerical tool in the hands of an engineer; DEM is used to resolve the soil as particles and CFD is applied for the depiction of the fluid phases. A critical issue on DEM-CFD simulations is the selection of a suitable homogenization coarse graining scheme, in other words a method to translate particulate mechanics into continuum mechanics. Within this contribution two novel porosity coarse-graining strategies are proposed including a Voxel method where a secondary dense grid of “pixel-cells” is implemented adopting a binary logic for the coarse graining and a Hybrid method where both analytical formulas and pixels are utilized. The proposed methods are compared with four porosity coarse-graining schemes that have been documented in the literature, including the Particle Centroid Method (PCM), an Analytical method, a method which solves the diffusion equation and an approach which employs averaging using kernels. A detailed comparison is then presented for all six schemes considering “accuracy”, “smoothness” and “computational cost”. Optimal parameters are obtained for all six methods and recommendations for coarse graining DEM samples are discussed.