Dynamic response of upper structures on 15 MW floating offshore wind turbine after mooring line failure

Mooring systems are indispensable for preserving the motion behavior and structural integrity of FOWTs. Its failure may lead to dangerous incidents such as platform capsizing and collisions with additional offshore facilities. Hence, it is essential to study the FOWT behaviors after mooring failure and to explore effective mitigation strategies. In this study, we established a fully coupled model for the IEA 15 MW semi-submersible FOWT. The model is employed to analyze the influence of mooring system failure on the motion and structural responses of the upper structure, including blade tip displacement, blade root and tower base bending moment, as well as generator power. Particularly, the influence of nacelle yaw system behavior and blade pitch emergency feathering were also discussed. It can be observed from the results that the transient responses suddenly and significantly increase after the mooring line is broken. Blade tip oscillations, bending moments on the blade root and tower base, as well as the generator output power all exhibit strong fluctuations, accompanied by a notable concentration of high-frequency energy. After yaw system shutdown, the fore-aft bending moment on tower base decreases significantly. Blade feathering effectively reduces both the blade root and tower base bending moments.