The influence of support structure dynamics on floating wind turbine performance

Abstract

A full-scale offshore wind turbine was simulated with two different floating platform concepts, a tension leg platform (TLP) and a floating spar, to examine the impact of platform motion on the rotor power performance. The study was restricted to regular wave conditions and constant wind speeds below the rated value. Combinations of the surge, pitch, and heave degrees of freedom were considered and simulated in FAST to determine the time-varying platform displacements. The latter were then prescribed to WInDS, a lifting-line free-wake vortex model. The means and peaks of the time series predictions for the rotor power coefficient under floating conditions were calculated both with FAST and WInDS. The results were compared to those under non-floating conditions. While the influence of the platform motion on the time-averaged rotor power output was found to be very small, the corresponding peak-to-peak values under certain conditions were found to be considerable.