Rigid obstacle impacted by a supercritical cohesive granular flow using a 3D discrete element model

Abstract

Abstract This study examines the drag coefficient of an obstacle impacted by a 3D cohesive granular flow using a discrete element model. A specific numerical setup is used to carry out reproducible and controlled normal impact simulations, in which the upstream flow properties are fully controlled parameters. The micromechanical contact model involves the physical properties of friction, normal elastic–plastic repulsion, dissipation, and a normal cohesion factor that induces bulk cohesion in the granular assembly. The effect of cohesion on the obstacle load is investigated through a micro-scale analysis. We show that increasing the cohesion leads to an increase of the obstacle drag, through a densification of the contact network, which enhances the transmission of contact forces to the obstacle. This experiment is extended to a wide range of supercritical flows, with Froude numbers between 1.5 and 11.2. The resulting drag coefficient curves are represented as power law functions of the Froude number. We then demonstrate the dependency of the power law exponent on the ratio between inertia and gravitational forces. Our results suggest that the assessment of drag coefficient critical values by conventional avalanche protection guidelines could be improved by a mechanical consideration of cohesion for certain snow types.