Granular erosion in Stokes flow and non-normal surface waves
Nick Moore, Florida State University

Fluid-mechanical erosion of solid material occurs across many scales, from massive geological structures down to tiny granular constituents. Here, we numerically examine the erosion of a granular medium in the Stokes limit — the regime of groundwater flow. We combine a highly-accurate boundary-integral formulation of the Stokes equations with stable interface-evolution methods. A single body erodes into a slender, for-aft-symmetric morphology which can be described analytical. Using the fast multipole method allows the simulation of 10-100 bodies. Many-body erosion naturally leads to the formation of channels and anisotropy in the medium conductivity. Time permitting, I will also discuss preliminary laboratory experiments on randomized surface waves over variable bathymetry. We find that bathymetry qualitatively alters wave statistics. An incoming, normal distribution of waves becomes highly skewed and non-Gaussian after encountering bathymetry. A theory awaits to describe these observations.