A coupling framework between OpenFAST and WEC-Sim. Part I: Validation and dynamic response analysis of IEA-15-MW-UMaine FOWT

This study proposes a coupling strategy between OpenFAST and WEC-Sim (OWS) to provide a general solution for the design of offshore floating wind turbines (FOWTs). The fully-coupled calculation is implemented by transferring the tower-base loads from OpenFAST to WEC-Sim, which in turn transfers the platform displacements, velocities and accelerations back to the former. The cross-platform data interface is achieved via S-function in Simulink, and a parallel route in OWS ensures a comparable calculation speed compared with OpenFAST. The model validation is conducted based on the IEA-15-MW reference wind turbine (RWT) and UMaine-VolturnUS-S semisubmersible platform with the reference site located at the northern North Sea. Through code-to-code comparisons against OpenFAST, the newly developed OWS model is tested in various environmental conditions to ensure its correctness and reliability. Furthermore, the dynamic responses of the FOWT are comprehensively investigated using spectral analysis. The time lag of the platform displacements with respect to the incident wave is quantitatively evaluated based on correlation analysis. Generally, there is little time lag between the heave displacement and the wave, but the time lag in the pitch direction (6–9 s) is approximately twice that (3–4 s) in the surge direction.