Modeling of Wave-induced Sediment Transport around Obstacles1

We report on further developments of a hybrid numerical model to simulate wave-induced sediment transport. A 2D numerical wavetank (NWT) based on fully nonlinear potential flow (FNPF) equations is used to simulate fully nonlinear wave generation and propagation. A 3D Navier-Stokes model with large eddy simulation (LES) is coupled to the NWT to simulate complex turbulent flows near the ocean bottom or around obstacles. Wave kinematics in the 2D-NWT thus forces flow simulations in the 3D-NS-LES model, and resulting sediment transport over the seabed and around a partially buried obstacle. The latter is calculated in a non-cohesive suspended load transport model simulating the (scalar) sediment concentration, using a constant settling velocity. The 2D NWT is based on a higher-order boundary element method (BEM), with explicit 2nd-order time stepping. The computational grid, thus, is the 2D-NWT boundary and the 3D-LES near-field domain. In the present new formulation, the total velocity and pressure fields are expressed as the sum of irrotational (incident/far-field) and near-field viscous perturbations. The LES equations are formulated and solved for the perturbation fields only, which are forced by the incident fields computed in the NWT. The feasibility of coupling the models in an efficient manner is demonstrated.