Reproduction of steep long crested irregular waves with CFD using the VOF method

The present paper aims to reproduce an extreme event extracted from an experimental time series relative to 2D long crested irregular waves. The experimental values are relative to the wave tank experiments at 1:80 scale, carried out on a stiff monopile within the Waveloads project. The monopile, modeled as a cylinder of constant diameter, is placed on a 1:25 slope and irregular waves are generated at the inlet with a mechanical paddle. In order to reproduce the time series and the consequent loads on the structure, a reconstruction of the wave elevation using a super position of 1st order components is done, the components are then imported to the aero-servo-elastic code 3Dfloat and the wave kinematics at the inlet for the computation fluid dynamics (CFD) simulations are obtained using 1st order formulation. Successively, the kinematics are imported as boundary conditions into the CFD commercial code STAR-CCM+. The free surface is modelled with the volume of fluid formulation and the k-co-turbulence model with the Menter formulation is used. In the experiments, a monopile of 0.75cm diameter (6m in full scale) is placed a distance of 7.75m (600m in full scale) from the inlet. The water depth at the model is 0.26cm (20m in full scale). Two different wave events of 25s extracted from two different time series are reproduced and compared with the experiments. The simulated wave elevation is measured at different locations and compared with the experiments. Good agreement between the simulations and the experiments is found. (C) 2017 The Authors. Published by Elsevier Ltd.