Damping Contributions of Semi-Taut Mooring for Floating Wind Turbines

Abstract In this paper, the energy dissipation characteristics of a semi-taut mooring for floating offshore wind turbines are investigated. The experiment is performed in a 2 m depth towing tank at the Memorial University of Newfoundland. The setup is scaled to 1 : 60 to represent a 120 m ocean depth. A model mooring line is set up in the semi-taut configuration, and a programmable linear motor, equipped with both force and position sensors, is employed to excite the mooring line horizontally in a sinusoidal manner. A load cell is installed with the mooring line to measure axial tension. A pre-tension is applied to the line to ensure it is in the desired initial state before sinusoidal motions are imposed. Varying low-frequency amplitudes and periods of oscillations are analyzed to assess the energy dissipation performance of the semi-taut mooring configuration. This is done using the indicator diagram approach, which estimates energy loss within the system. The results reveal that energy dissipation is higher at shorter oscillation periods due to stronger drag forces but decreases with longer periods as the motion becomes quasi-static. The equivalent linear damping coefficient was derived, showing an inverse trend with energy dissipation: lower coefficients at shorter periods with rapid cycles and higher coefficients at longer periods due to extended damping time.