Overtopping device numerical study: Openfoam solution verification and evaluation of curved ramps performances

Abstract

The Overtopping Device is a type of Ocean Waves Energy Converter (OWEC) which concept is storing water provided by incident waves above sea level to feed a set of low head turbines. Present study aims to perform 2D numerical analyses of near-shore overtopping devices platforms to investigate the influence of curvature of the platforms on water discharge by means of OpenFOAM code, which is an open source software. Current study performs comparisons between Fluent and OpenFOAM solutions as well (first part of results). Therefore, pointing out OpenFOAM as a potential tool for simulation of overtopping devices is also one of the objectives of this study. The software comparison is performed based on a case found in literature considering seven linear overtopping platforms configurations inside a wave tank. The discretization method is the Finite Volume method solving momentum, continuity, and a water volume fraction (Volume of Fluid method) equation used to capture waves air–water interface. Platforms curvatures investigation considers 12.5 m and 25 m length devices, with three different shapes: concave, linear and convex. All of those are 6 m height with 5 m immerse and 1 m above water level. The ramps are submitted to incident regular waves (1 m height, 65.4 m length and 7.5 s period) inside a 10 m depth wave channel. Results showed that OpenFOAM wave model complies with the expected characteristics determined with mathematical classical equations and also it is very coherent with Fluent results. About the ramps shapes, it was observed that ramps curvature may maximize the water mass that overtops into the tank. Moreover, this study agreed with literature that lower ramp height/length ratio leads to water discharge improvement for linear ramps for specified wave and constructions conditions. Other important observation is that curved platforms usage is a very good option to reduce devices sizes without losing energetic potential. This is pointed out because the convex 12.5 m length, which has length/ratio bigger than 25 m length devices, achieved the greatest water discharge among the analyzed geometries.