Mooring analysis in offshore floating labs: Case study on a 15 MW wind platform

As floating offshore wind turbines (FOWTs) expand into deeper and more complex marine environments, validating mooring system performance under real-world conditions becomes critical. This study investigates whether the purposely designed offshore floating laboratory (OffLab), named ACTOR, can serve as an effective and conservative testbed for mooring line evaluation. ACTOR is a conceptual platform inspired by the floater of the UMaine VolturnUS-S 15 MW semi-submersible FOWT design. The dimension of the ACTOR is about one third of the 15 MW semi-sub floater and is intended deployment in a nearshore UK site with milder sea conditions. Using site-specific environmental data from two locations—the full-scale deployment zone in the Celtic Sea and a nearshore test location near Plymouth Sound—we perform comparative mooring analyses with OrcaFlex. Extreme load cases are defined using Direct-IFORM environmental contours, and fatigue conditions are derived from long-term wave spectral clustering. Results show that due to shallow water effects and tailored pre-tensioning, the ACTOR platform can replicate or exceed the mooring line tensions and fatigue damage accumulation observed in full-scale systems. The findings demonstrate the potential of ACTOR as a physically accessible, cost-effective platform for accelerated offshore component testing.