Effect of the surrounding fluid on the compaction of granular materials by tapping: Slow dynamics made slower?

Abstract

We investigate compaction due to tapping in two-dimensional granular columns computationally with the discrete element method (DEM) in two dimensions. We compare the compaction in dry granulates with the compaction of the system immersed in a viscous fluid. We use polygons as particle shapes, so that the resulting pore-space can be triangulated for a finite element method (FEM) for an incompressible fluid. We investigate the competition between a slowing-down of the dynamics due to the viscous forces of the fluid and the improved transmission of the tapping pulses through the fluid in the pore space. For the system immersed in water, the propagation of the shocks due to the tapping of the floor is faster than in the corresponding dry system. The center of mass of a nearly square system drops faster for the dry case than for immersed particles. For a system twice as high and half as wide, for the same vibration, for the dry system, the center of mass rises, while for the immersed particles there is hardly any change.

Simulating Free Boundaries in 2D FEM Flow Simulation with Direct Time Integration of the Surface Velocities

“…If the fluid front moves too fast, so that such a center point ends out of the fluid domain of the previous timestep, interpolation is not possible: The timestep must therefore be chosen to avoid that the middle points move too far. We have not quantified the restriction on the timestep, as it is due to the physical time scales: When we simulate the shock propagation in an aggregate of particles in fluid [14], the timestep is related to the speed of the shock propagation (which is of the order of percent of the continuum sound velocity): For harder materials (higher Young's modulus), or "stronger" Figure 3. Free surface modeling: moving the surface of the fluid using the obtained velocities from the finite element method.…”