Analysis of platform motion effects on fatigue loads and aerodynamic unsteadiness in 15 MW novel floating offshore wind turbines with transient impact

This study investigates the fatigue behavior of an ultra-large 15 MW semi-submersible floating offshore wind turbine (FOWT) under various transient scenarios, including startup, shutdown, and fault conditions, which are often overlooked in conventional analyses. A high-fidelity simulation framework was developed, integrating TurbSim for three-dimensional wind field, OpenFAST for aero-hydro-servo-elastic load simulation, and MLife for fatigue assessment via damage equivalent load (DEL). The results show that platform motion has a negligible impact on power output but significantly affects structural responses. Compared to fixed platforms, moving configurations reduce blade-root fatigue by up to 41.83 % during rotor idling and tower-base fatigue by up to 3.29 % under fault-induced shutdowns. In contrast, shutdown transients can amplify tower-base shear and bending DEL by up to 54.16 % and 62.26 %, respectively, especially at high pitch rates. Overall, moving platforms demonstrate superior fatigue mitigation and more uniform load distribution, particularly during abrupt shutdowns or rotor imbalance. • Comprehensive analysis of a novel 15 MW semi-submersible FOWT, comparing damage equivalent load (DEL) under transient events. • Moving platform minimally affects power performance but significantly alters structural fatigue, especially at the tower-base. • Moving platform reduces DEL by suppressing high-frequency resonances and enabling load redistribution.