Dynamic response of a floating offshore wind turbine under multi-stage typhoon conditions: A case study of super typhoon In-Fa

Floating offshore wind turbines (FOWTs) are essential for achieving long-term renewable energy targets, yet their resilience to extreme weather events, especially typhoons, remains a key challenge. This study investigates the dynamic response of a 5 MW semi-submersible FOWT under the multi-stage passage of Typhoon In-Fa. Site-specific environmental fields are reconstructed using a triple-nested WRF model coupled with TurbSim, driving OpenFAST simulations to evaluate a novel low-rotor-speed control strategy against the conventional parked strategy. The Front Eye Wall stage (FEWS) is identified as the dominant loading condition. Results reveal a complex structural trade-off: while low-rotor-speed operation increases mean loads, it mitigates peak tower-base shear forces through aerodynamic damping. Conversely, the parked mode suffers from amplified transient peaks and sensitivity to lateral wind veer. Crucially, mooring safety is compromised in both states, with peak tensions exceeding DNV criteria; this overload is primarily driven by large platform surge excursions, which arise from the superposition of aerodynamic thrust-induced mean drift and wave-driven low-frequency oscillations. These findings highlight that standard parking strategies may be insufficient, underscoring the need to balance aerodynamic damping benefits with enhanced mooring capacity in typhoon-resilient designs. • Multi-stage typhoon fields reconstructed via triple-nested WRF-TurbSim coupling and JONSWAP waves. • Aerodynamic damping in low-rotor-speed mode suppresses transient tower loads despite higher mean thrust. • Peak mooring tensions are governed by low-frequency surge driven by combined wave-wind drift. • The Front Eye-Wall Stage acts as the dominant governing condition for ultimate limit states. • Both parked and operational strategies fail DNV mooring safety checks, necessitating enhanced damping designs.