Dynamic Power Cable Layout Design for 15 MW Floating Offshore Wind Turbines: Part 2 - Evaluation of Ultimate Limit State Performance

This study presents an ultimate limit state (ULS) assessment of two optimal dynamic cable layouts, previously proposed by the authors, for a 15 MW floating offshore wind turbine (FOWT). These configurations were evaluated under 50-years return period extreme conditions representative of the Ulsan offshore region. Dynamic cable was modeled using MoorDyn, and fully coupled time-domain simulations were conducted in OpenFAST, accounting for interactions among the FOWT, mooring system and cable. Each layout underwent twelve 3-hour simulations across four sub-DLCs with varying wind and wave phase combinations. Both layouts satisfied all design constraints, with horizontal offsets staying within the ULS criterion of 30% and tension and curvature remaining within acceptable ranges under a safety factor of 2. Higher hang-off tension and Ez angle occurred under upwind conditions, especially in the 230% buoyancy configuration. Sag and hog bend points showed inverse tension-curvature relationships influenced by horizontal offset, with the 230% layout exhibiting lower curvatures due to extended buoyancy distribution. At TDP (touchdown point), wave/current directions governed curvature while horizontal offset controlled tension. Statistical analysis of TDP variability determined optimal cable lengths for both configurations. Future work will extend to fatigue limit state (FLS) evaluation under normal operating conditions to ensure long-term durability.