Mooring system analysis for a 15 MW semi-submersible floating offshore wind turbine in deep-sea deployment: Case study for Morro Bay Wind Energy Area, California

Floating Offshore Wind Turbines (FOWTs) can harness high-quality wind resources at deep water sites, exemplified by the Morro Bay Wind Energy Area (WEA) in California, where depths exceed 1000 m. Such deepwater deployments present engineering challenges for reliable mooring systems that must withstand extreme, site-specific environmental conditions throughout the FOWT’s operational life. This study presents a comprehensive framework for analyzing and optimizing a 15 MW semi-submersible FOWT mooring system at the Morro Bay site. It adheres to industry standards (ABS, API, IEC, DNV) for ultimate, accidental, and fatigue limit state calculations. Site-specific metocean data was used in the study for tailored design load cases. In addition, a novel “directional” load case, to ensure a realistic performance assessment through mid-fidelity coupled simulations in OrcaFlex. A key contribution is the integration of multi-objective optimization using modeFRONTIER to enhance mooring fatigue life, addressing initial findings that the upwind line fell short of its design life. The proposed framework provides a robust, practical design approach for FOWT projects in onerous deepwater ocean environments by combining industry compliance, detailed environmental modeling, and advanced optimization to deliver efficient, tailored solutions.