Numerical prediction of wave excitation forces on a fixed tension leg platform concept for offshore wind turbines

To predict wave excitation forces on a fixed Tension Leg Platform Wind Turbine (TLPWT), two numerical software packages were used, namely the CFD code STAR-CCM+ and ANSYS AQWA. The CFD code solved the fully-nonlinear Navier-Stokes equations in a time domain whereas ANSYS AQWA solved the linear diffraction problem in a frequency domain. In both domains, the horizontal wave excitation forces on a generic TLP structure under several deterministic regular wave conditions of a mild sea state were predicted. The size of the mesh/panel was fine-tuned to yield optimum results for both solvers. It was found that the horizontal forces obtained by the linear diffraction solver were larger in magnitude than CFD predictions. The linear diffraction solver provided an insight into the horizontal force experienced by the TLP structure, and hence it could be used to verify CFD results. However, as the linear diffraction theory does not account for the effect of turbulence, viscous effects or the effect of the air phase, CFD codes could be used to investigate such phenomena and provide further details.