Evaluation of load reduction performance according to the modeling approach of the mooring load reduction device

초록

The mooring system of a floating offshore wind turbine (FOWT) constitutes a major share of capital expenditure, particularly for catenary moorings. To address this, load reduction devices (LRDs) have been proposed. This study conducts a stepwise evaluation of LRD performance. A 15 MW semi-submersible FOWT with three catenary mooring lines was modeled using rigid elements for the platform and beam elements for the mooring. Environmental loading was applied under DLC 6.1. Based on the results, a three-phase stiffness curve was designed, and its load reduction effect was verified using a nonlinear spring LRD model. An LRD with realistic geometry and multi-body dynamics (MBD) was modeled. This device consisted of a cylindrical buoy and two hinged arms modeled with rigid elements and joint elements. Beam elements were included to account for buoyancy and drag forces acting on the buoy. Pulling simulations confirmed that the stiffness response was strongly influenced by the center of mass location and arm angle. Finally, the MBD LRD was integrated into the FOWT model for load analysis. The results showed that excessive oscillations of the LRD were induced by FOWT motions, leading to an increase rather than a reduction in mooring loads.

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