Fragility and vulnerability development of offshore wind turbines under aero-hydro loadings

Wind technology is an effective solution for the carbon neutral over the world. Offshore wind turbines (OWTs) have therefore seen unprecedented development over the decades. Fragility and vulnerability of OWTs are vital in structural performance evaluation and risk assessment of infrastructural systems under natural hazards. Previous research mainly focused on the fragility of OWTs with monopile substructure in the normal operating or parked conditions. In the present study, a realistic situation with respect to the emergency shutdown mode is considered for the OWTs with monopile, tripod, and jacket substructures. A procedure to establish fragility and vulnerability models is developed. Numerical models using a combination of FE software are implemented and validated for dynamic analyses and pushover analyses. Then, the fragility and vulnerability models of the main structural subsystems including rotor, nacelle, tower, and substructure are separately established according to the developed procedure, so as to the fragility and vulnerability models of the whole wind turbine. Besides, impact of operational condition and characteristics of substructure on fragility and vulnerability is comprehensively compared and discussed.