Experimental study of the dynamic response of a spar buoy floating structure under wind and wave action

Floating Wind Turbines (F-WT) represent an important trade-off in terms of wind energy potential and economic feasibility. Among the floating concepts, Spar Buoy (SB) wind turbine is particularly suitable for deep waters. The motion response of such a structure depends on wind, wave and rotor conditions. Nowadays, only a limited number of experimental studies have been conducted on the dynamic response of F-WT even if the recent interest in renewable energies has increased the demand of quality physical model tests to optimize the design of innovative F-WT and to collect reliable and accurate data for further calibration and verification of numerical models. In the present work, the experience gained from the conduction of a 3D physical model experiment performed within the EU-Hydralab IV Integrated Infrastructure Initiative (http://hydralab.eu/) will be described. The objectives of the research activity have been mainly oriented: (i) to investigate the dynamic behavior of a SB floating structure and (ii) to overcome the limitation in the available public domain dataset. Observations of displacements of the floating structure and wave/wind induced tensions at the mooring lines have been carried out. In the present study, a frequency domain analysis is conducted in order to investigate the dynamic effects on the SB under co-directional and misaligned irregular waves/wind loads and extreme conditions. In particular, waves head in two directions, 0° and 20°, respectively, with reference to the structure. The results show that the dynamic response of the SB wind turbine in coupled wave-wind-induced analyses is influenced by both wave and wind loads effects.