Mooring Tension Analysis and Reliability-Based Design of Multiline Anchors in Floating Wind Farms

Abstract

Multiline anchors allow for the mooring of multiple floating offshore wind turbines (FOWTs), offering a cost-effective anchoring solution for large-scale floating offshore wind farms (FOWFs). However, their design is challenged by nonlinear load interactions and significant uncertainties in environmental and soil parameters. This necessitates a systematic exploration of the relationship between environmental parameters and mooring tensions, as well as the development of a reliability-based design framework for multiline anchors. This study quantifies the influence of wind speed, significant wave height, current speed, and load application angle on mooring tensions for single-line and multiline anchors using a 5-MW spar-type FOWT with a catenary mooring system, considering 4,180 combinations of environmental parameters. A new active-learning Kriging method is developed to construct accurate surrogate models that efficiently capture the nonlinear relationship between environmental parameters and mooring tensions, and is integrated into a reliability-based design framework. The proposed framework is applied to a representative FOWF consisting of seven FOWTs. The results reveal that wave height dominates the maximum mooring tension at windward mooring-line-connected anchors, whereas wind speed governs the maximum mooring tension at leeward mooring-line-connected anchors. For the top-mooring case, in which chain–soil interaction is neglected, the design diameters of multiline anchors are smaller than those of single-line anchors due to counterbalanced horizontal loads. In contrast, in the optimal-mooring case, where chain–soil interaction is considered, the design diameters of multiline anchors are larger because of the superposition of vertical load components.