Simulation of breaking focused waves over a slope with a CFD based numerical wave tank

Abstract

Extreme wave conditions are always identified with large-amplitude breaking waves in shallow waters. Focused waves can often be used to describe extreme waves which evolve during the nonlinear wave-wave interaction, occurring at one point in space and time. Understanding breaking focused waves has many design-related implications for the design of offshore wind turbine (OWT) substructures in shallow waters. The main objective of the paper is to model breaking focused waves over a sloping seabed and study the breaking characteristics using the open-source CFD model REEF3D. The numerical model describes the two-phase flow using the incompressible Reynolds-Averaged Navier-Stokes (RANS) equations together with the continuity equation. The model uses a fifth-order WENO scheme for convection discretization and a third order Runge-Kutta scheme for time discretization along with the level set method to obtain the free surface, yielding accurate wave propagation in the numerical wave tank. Solid boundaries are accounted through the ghost cell immersed boundary method. The free surface is modeled with the level set method. Turbulence is described with the two-equation k − ω model. In the numerical wave tank, the focused waves are generated using a single flap-type maker theory. The numerical results are in good agreement with experimental results for complex free surface elevations measured at several locations along the wave tank. The numerical aspects related to the development of the breaking process are investigated together with the evolution of focusing wave group in the numerical wave tank. Further, the study also examines the free surface flow features that evolve during the breaking process.