Wave overtopping numerical simulation using openfoam

Nikolaos Karagiannis, Theofanis Karambas, Christopher Koutitas

Tuesday 30 june 2015

10:00 - 10:15h at South America (level 0)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 4J. Floodrisk – Flooding

The aim of this work is to investigate the behavior of a numerical model, synthesized on the basis of OpenFoam, for the simulation of the wave propagation above an inclined impermeable structure (breakwater or Wave Energy Converter (WEC) structure) and the calculation of the wave overtopping rate. The simulation of the above flow is made with the open source toolbox OpenFoam and the additional wave generation toobox waves2Foam (Jacobsen et al 2012). The geometry of the model was created using standard OpenFoam tools (blockMesh and snappyHexMesh – extrudeMesh) for the breakwater. WaveFoam solver of waves2Foam toolbox based on InterFoam solver with the respective VOF method was used to track the free surface and k-omega SST model for incompressible flow, available in OpenFoam libraries, was modified in order for the density to be included in model's equations. The simulation of the free surface was considerably improved using the above modified model. Furthermore, suitable boundary and initial conditions were chosen with the appropriate one for the wave generation at the inlet, available in waves2Foam libraries. Surface elevation and depth averaged velocities are obtained from the model and the average overtopping rate is calculated and compared to semi-empirical formulae from literature. Iribarren number as a criterion of breaking waves, the slope angle, freeboard in relation to wave height, and the wave steepness are the most important factors which determine the average overtopping rate. A slope of 1:1.73, namely 30o angle, which considered optimal for the wave overtopping, is implemented in the model. A wave steepness of around 0.033 is regarded as optimal for the maximum overtopping rate as well. Extended investigation on wave characteristics and freeboard was made and the model results are compared satisfactorily with empirical formulae. References : 1. Jacobsen, N.G., Fuhrman, D.R., & Fredsøe, J. (2012). “A Wave Generation Toolbox for the Open-Source CFD Library: OpenFoam” Int. J. Numerl. Meth. Fluids,70(9): 1073–1088.