Experimental investigation into the dynamic behavior of a floating offshore wind turbine stabilized via a suspended counterweight

Abstract

Ocean engineers are often tasked with developing innovative, low-cost floating offshore wind turbines as the industry moves toward deeper waters to access regions with higher offshore wind potential. One example is the hanging-mass concept, in which a suspended counterweight stabilizes a positively buoyant floater; a hybrid design that combines a spar's performance with the maneuverability of a semi-submersible. Simultaneously, using elastic cables instead of a rigid support structure to support a low center of mass presents the opportunity for cost savings. This work presents experimental results from tests conducted on a 1/48-scale model of a conceptual hanging-mass floating offshore wind turbine design. Compared with traditional platform designs, the hanging-mass's response amplitude operators (RAOs) show a generally better response in heave and pitch, as the natural periods occur well outside the wave energy range, unlike the other platforms examined. Comparison between the line tension RAOs for systems with different suspension line stiffness indicate that softer systems experience larger tension fluctuations at low periods while the inverse is true for stiff systems. Finally, response spectra show that high-frequency modes describing relative motion between the two bodies are excited by irregular waves, likely due to sum-frequency second-order effects.