Investigation of mooring breakage impact on dynamic responses of a 15 MW floating offshore wind turbine

Abstract

The stability and integrity of the mooring system are some of critical factors affecting the safety and performance of floating offshore wind turbines (FOWTs). For this reason, it is necessary to investigate the dynamic responses of the rotor, platform, and the remaining cables of the FOWT subjected to mooring breakages. This is because a mooring breakage significantly increases the risk of damage to the FOWT, especially for a nonredundant mooring system. This study has analyzed the platform motions and mooring tension of a 15 MW FOWT, where each offset column connects to two and three mooring lines to enhance the redundancy of the mooring system. The fully coupled simulations of the FOWTs under mooring breakage scenarios are examined using the well-validated numerical framework, OpenF2A, to consider wind, wave and current loading combinations. The result reveals that the breakage of a single mooring has a minor impact on the aerodynamic performance and aeroelastic response of the FOWT for both mooring system configurations. Notably, the platform experiences significant surge and sway when the upwind mooring breaks, leading to a sharp increase in tension of the remaining mooring lines positioned in the same direction. Moreover, the occurrence of snap load events is another factor resulting in the abrupt increase in the mooring tension. However, the maximum tension in the remaining mooring lines has not exceeded the threshold of breaking stress for both redundant mooring systems. The mooring configuration with two catenary cables connected to each column is suggested for the station-keeping system of the 15 MW FOWT considering the dynamic behavior and manufacture cost.