Extended Dynamic Response Analysis of the IEA 15 MW Semi-Submersible Floating Offshore Wind Turbine Across Misaligned Wind–Waves

This study maps the dynamic response of the IEA 15 MW reference wind turbine mounted on the UMaine VolturnUS-S semi-submersible platform across seven wave headings, spanning β = 0–180°. A fully coupled aero–hydro–servo–elastic OpenFAST model with lumped-mass catenary mooring is simulated over three environmental groups: below-rated operation, a severe sea state at rated wind, and a parked extreme, combined with seven wave headings and supplemented by a 77-case operational envelope sweep across hub wind speeds of 4–24 m/s. Responses are analyzed through time-domain and frequency-domain statistics, drift kinematics, and exceedance curves. At operating states, the maximum side-to-side moment rises from 80.44 to 273.60 MNm between following and beam seas, while the maximum fore–aft moment reduces from 566.90 MNm to 485.23 MNm, respectively. The parked extreme LC-C maximum pitch response (2.77° at following seas, 2.59° at beam seas) is roughly half that of the severe operating LC-B (6.29° and 5.38°, respectively). This directional coupling is robust across environmental severities. In the parked group, the lateral motions (sway, roll) are amplified, as feathering reduces the rotor’s aerodynamic contribution to lateral damping. The developed wind speed misalignment response atlas condenses the aforementioned data, providing a compact basis for rapid early screening of ultra-large floating offshore wind turbines.