Investigation on mooring breakage effects of a 5 MW barge-type floating offshore wind turbine using F2A

Abstract

Stability and integrity of the station-keeping system are vital to the safety and performance of a floating offshore wind turbine (FOWT). Failure of a mooring line significantly increases the risk of damage to the FOWT. Consequently, it is necessary to investigate the impacts of a mooring breakage on dynamic responses of the rotor, platform and the remaining mooring lines of a FOWT. In order to address the associated research needs of a FOWT subjected to mooring failures, this study has analyzed and predicted the transient behaviors of a 5 MW barge-type FOWT under rated and extreme conditions using a coupling framework based on FAST and AQWA (F2A) when a mooring is subjected to a sudden breakage. It is found that the mooring breakages have a minor impact on the aerodynamic performance and aero-elastic responses of the FOWT, although a notable yaw-deviation of the rotor is caused. The platform sway and yaw motions are significantly influenced by the breakage of an upwind mooring line. Thus, the tension in the remaining adjacent mooring line is increased by as much as 156% and 41.6% under the examined rated and extreme conditions, respectively. The emergency shutdown following the mooring line breakage decreases the platform drift and yaw motions, while the platform pitch motion is enhanced by the shutdown measure due to the absence of aerodynamic damping. In addition, significant reductions in the tensions of upwind mooring lines that suffer the most severe tension are achieved. The shutdown measure is beneficial in ensuring the operational safety of the FOWT subjected to a sudden breakage of a mooring line.