Methodological and Technical Aspects of a Two-Degrees-of-Freedom Hardware-In-the-Loop Setup for Wind Tunnel Tests of Floating Systems

This paper presents the methodological and technical aspects of the implementation of a hardware-in-the-loop experimental setup, suitable to simulate the dynamics of a floating system in wind tunnel experiments. The presented work is based on the specific application of a floating offshore wind turbine scale model, even if the approach holds also for floating systems in general, being subjected to the simultaneous action of wind and waves. The setup is based on a two degrees-of-freedom system, providing the motion of the floating system along surge and pitch. With reference to the implementation of the HIL test methodology the following topics are thoroughly analyzed: scaling issues, numerical issues, mechanical system characterization, force corrections, measurement, and signal processing. For each of these topics the methodological approach is presented, and the technical issues are described. A subset of results is then reported to show the effectiveness of such experimental apparatus, for different sea states: still water, regular, and irregular waves.