Buoy effects on low-frequency dynamics of catenary moorings for floating offshore wind turbines

In this paper, experimental results on the dynamic response and damping behaviors of mooring lines with forced horizontal oscillations are presented. To represent conditions representative of a floating wind turbine, experiments were conducted at 1:60 scale in a 2 m deep towing tank using two mooring configurations: a bare catenary and a buoy-assisted catenary. Sinusoidal surge motions were imposed at the fairlead using a programmable linear actuator, covering a range of amplitudes (0.083–0.417 m) and periods (6.455–38.730 s). Fairlead tension was measured using an in-line load cell, while top-end angles were extracted from high-speed videos at 100 fps. Energy dissipation was quantified from force–displacement cycles using indicator diagrams. Results show that the bare catenary dissipated more energy at smaller amplitudes, while the buoy-assisted configuration became more effective at higher amplitudes due to a transition into a taut regime. Slack–snap behavior observed in the buoy-assisted case led to nonlinear responses and dynamic tension peaks up to 8.23 times the minimum value. The bare catenary had a strong linear relationship between dissipated energy and the excitation parameter, ω 2 q 3 .