In the previous study, we have investigated the transient dynamic behaviors of a SPAR-type FOWT under a particular accidental scenario when the freak wave is followed by the sudden failure of one mooring line. In the present work, we further investigate the influence of the sequence and gap time between both accidents, based on a coupled aero-hydro-elastic numerical model. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a fully nonlinear dynamic algorithm for intact and fractured mooring lines. The freak wave is regenerated by an improved phase modulation approach. According to the numerical simulation results, the dynamic performance of the FOWT, including the oscillations and drift motions of buoy, aerodynamic loads on rotor and mooring tensions are discussed among the cases when the freak wave and mooring failure happened in different turns. According to the results, the freak wave, as well as its occurring time, will hardly affect the final equilibrium position which is caused by the mooring loss.


During the past decades, the fossil energy challenge has become more and more critical, due to its storage shortage and air pollution issue. Hereby, more attentions were paid to renewable and sustainable energies, such as wind, solar, wave, tide, etc (Chen et.al, 2020, Kannan and Vakeesan, 2016, Zhang et.al, 2020). Among these no-carbon-emission solutions, the wind energy, including both onshore and offshore one, takes the preemptive development opportunities at the beginning of the twenty-first century. In order to capture the wind energy in the deep water area, where the strength and robustness of wind are much better than other areas, the floating offshore wind turbines (FOWTs) are taken out to fix the disadvantages of the fixed wind turbines in the deep water areas, for example, the costs and difficulties of the installation and maintenance (Leimeister et.al, 2020).

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