Influence of floater response on wind turbine tower moments in floating wind turbine system

Abstract

The study uses finite element modeling to discuss the effect of floater response on tower moments in a floating offshore wind turbine system. A semi-submersible floating platform supporting a single NREL-5MW wind turbine was investigated. In order to understand the contribution of different modes of floater motion to tower load, tension leg mooring and catenary mooring were used. The mooring systems were designed to provide similar dynamic response amplitude in surge, while the pitch response was inherently different. Wind and wave loads were considered separately and then together to identify their respective contribution to response and tower loads. Both wind and wave loads were found to be critical for tower base moment while wind loads govern the tower top moments. In comparison with catenary mooring, the tension leg mooring was found to reduce the tower base moment by up to 50 % at higher wind speeds due to restraint to pitch motion. The two types of mooring provided a similar tower top moment which indicates it is independent of pitch motion.