On the effects of wind and operating conditions on mooring line tensions for floating offshore wind turbine

The present work addresses a significant topic in the current understanding of the structural dynamic behavior of mooring lines for floating offshore wind turbines (FOWT) in operating condition and aims to contribute to the ongoing efforts to enhance the performance and reliability of floating offshore wind energy systems. The present paper investigates the impact of operating conditions on mooring line tension for FOWT. A numerical model of a spar-type FOWT developed in Orcaflex, validated with experimental data, was employed to perform dynamic analyses and to calculate the most probable maximum tension values for scenarios involving wave-only and combined wind-wave actions under various operating conditions. Results indicate that the peak frequency of oscillations is primarily influenced by wave frequency and remain unchanged in operating conditions, but the significant variability in the structure's displacement response leads to a notable fluctuation in tensions within the mooring lines. Specifically, higher tensions are observed in the upwind region while lower tensions are evident in the downwind area. However, for prolonged periods it becomes apparent that operating conditions induce high tension levels across all mooring lines, while also exerting a damping contribution related to wave-induced effects. The study underscores that the primary detrimental factor affecting mooring lines in operating conditions is the widening of the operating tension range.