Statistical Characterization of the Motion of Sediment Particles in Oscillatory Flows.

The dynamics of sediment particles in the nearshore is strongly determined by coherent structures of the turbulent boundary layer. These vortices are driven by the oscillatory flow imposed by the global pressure gradient, and they are characterized by intense near-bed velocity fluctuations. In this scenario, the dynamically rich flow produces an instantaneous increase of the shear stress, which imprints changes on the acceleration of the particles. Detailed approaches for the sediment dynamics, coupled with high-resolution models for the flow can help to understand the statistics of particle motion as a function of the non-dimensional parameters that characterize the flow (e.g. Stokes number, particle Reynolds number, Shields number and Sleath number). In order to increase our understanding on these transport processes, we developed a Lagrangian sediment transport model to simulate particle motion on a flat bed channel under oscillatory flows. We couple direct numerical simulation (DNS) to solve the 3D Navier-Stokes equations for the flow and the discrete element method (DEM) to solve the particle dynamics (LIGGGHTS, http://www.cfdem.com/liggghts), using a two-way coupling approach. The objectives of this study are: i) to make a detailed description of the first and second-order statistics of the near-bed sediment motion in oscillatory flows, and ii) to explore the variations on the space and time correlations between the particle dynamics and the instantaneous hydrodynamic forces in bedload transport.

This work was supported by Conicyt National-PhD Grant - 21120939, Fondecyt grant 1130940 and ONR-G NICOP Project N622909-11-1-7041.