Modeling solitary wave transformation and run-up over fringing reefs with large bottom roughness

Abstract

Field observations over decades have found that the surface roughness of coral reefs is typically one or two order of magnitude larger than that of sandy beaches. To better reproduce the solitary wave transformation and run-up over fringing reefs with large bottom roughness, a numerical wave tank based on the CFD tool OpenFOAM® is developed in this study. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved for two-phase incompressible flow with the k-ω SST model for the turbulence closure and VOF method for tracking the free surface. The reef surface with high friction is modeled by coupling a porous media model in the RANS equations. The model is first validated by our new performed laboratory experiments as well as a laboratory dataset in the literature. A fixed set of model parameters is found to be suitable for both experiments. Subsequently, the model is applied to evaluate the impacts of hydrodynamic, morphological and roughness element factors on the wave run-up on the back-reef beach, and an empirical formula is proposed to predict the wave run-up based on the simulations. Finally, the cross-reef variations of flow and vorticity fields under the breaking solitary waves are also examined via the numerical simulations.