Investigating the influence of mooring design on floating wind turbine aerodynamics

Abstract

Mooring lines are essential in the design of Offshore Floating Wind Turbines (OFWT). These provide both the necessary station-keeping and stability to the structure. Hence, understanding the influence of the mooring configuration on the whole OFWT is crucial to balance energy generation and costs. In this dissertation, a simulation analysis was done to analyse the effects incurred on the aerodynamic performance of a semi-submersible platform with regards to the mooring design. An OFWT was modelled using ANSYS Aqwa which uses hydrodynamic diffraction and radiation principles to compute the hydrodynamic loading on the structure. The aerodynamic loads were computed using an open source free-wake vortex code, Wake Induced Dynamic Simulation (WInDS) in which the unsteady aerodynamic wake was modelled using free wake vortex methods with which the aerodynamic loads on the rotor were computed. A manually coupled model was developed which combined the hydrodynamic loading and the aerodynamic performance of the OFWT. The model was validated with literature to ensure that the results were as close as possible to those observed in reality. Tests were compiled for different mooring conditions in different wind and wave environments. Using the results obtained for the thrust and power generated by the OFWT together with the displacements of the OFWT in the surge, heave and pitch degrees of freedom, the influence of the mooring design was analysed.