Newton vs Stokes: competing forces in granular matter

Granular materials can be encountered everywhere and are very important in industry. The first step in understanding these materials is normally to focus upon gravity and mechanical contact forces only. While this is a valid approximation when the particles are large, for smaller particles also the ambient air has a pronounced influence and must be taken into account. In this thesis we focus on particles where the “Stokesian” forces (drag, air pressure) and the “Newtonian” forces (from collisions and gravity) compete for dominance. Two examples that illustrate this in a particularly clear manner are the formation and coarsening of Faraday heaps and the appearance of regular and inverse Chladni patterns on a resonating plate. We study these systems by a hybrid Granular Dynamics – Computational Fluid Dynamics numerical code and compare the results with experiments. The simulations enable us to provide detailed explanations for these phenomena.