Investigation Of Wave-current Loads On The Offshore Wind Turbine Foundation Structure

The offshore wind power generation has just taken the first step in China, andmany engineering problems about the construction of supported structures need to besolved urgently. In addition to the wind forces transferred down by the wind turbine,the supported structure is also suffering with the load of combined waves and currents.Therefore the investigation on the load of supported structures of wind turbine due tocombined waves and currents would be of great significance for the development ofoffshore wind farm. Based on the open source code of OpenFOAM, a three-dimensional numerical wave flume and a three-dimensional numerical wave-currentflume are developed. The interactions among waves, current and supported structuresof wind turbine are investigated through numerical simulation. The main contents andconclusions of the thesis are as follows.(1) The interFoam, a two-phase flow solver of OpenFOAM is used to solveuncompressible Reynolds Averaged Navier-Stokes Equations(RANS). Themomentum distribution source term is introduced into the momentum equations forwave making. The VOF method is used to capture the free surface motion. Then, athree-dimensional numerical wave flume is developed.(2) Through a series tests, optimal time and space steps are chosen forthree-dimensional wave numerical models: Space step in horizontal direction is L/100;vertical step within the scope of wave height depends on the length-width ratio of thegrid, and the recommend ratio is about1.8; the vertical steps for the rest grids isgradually diminishing; the time step can dynamically vary with the maximum step ofT/100, and meanwhile Courant number is limited less than0.2.(3) The developed model is applied to simulate the wave field around a cylinderpile, and the wave heights, velocities and pressures are obtained. The simulated resultsagree with the experimental data well. It can be shown that the interaction betweenwaves and structures is simulated by the numerical wave flume satisfactorily.(4) On the basis of the numerical wave flume, a three dimensional numericalwave-current flume is developed through setting up entrance flow and outflow on thebottom. The simulated waves and current velocity distribution agrees with theexperimental results. (5) The three dimensional numerical wave-current model is applied for theinvestigation on wave and current loads of the complex bucket foundation structuressupporting the wind turbine in Xiangshui, Jiangsu. The characteristics of flow andforces around the complex bucket foundation structures, under the action of waves,current and combined waves and current are analyzed.