Dynamic response of three floaters supporting vertical axis wind turbines due to wind excitation

Abstract

Floating vertical axis wind turbines (VAWTs) are potential solutions for wind energy harvesting in deep-water oceans. The platform design has a great impact on the overall dynamic behaviors of the system. In this study, the dynamic responses of three floating VAWT models under wind excitations were tested in a water tank facility. A three-bladed H-rotor VAWT model with a geometric scale of 1:100 was used and fixed onto three floating platforms inspired by offshore oil rigs and floating wind turbine prototypes. The three platforms, i.e. single-spar, tri-floater, and hepta-spar, represent a deep draft, a strong buoyancy, and a hybrid conceptual model, respectively. The natural frequency of these models has been determined in free-decay tests. In the experiments, six degrees-of-freedom forces/moments were measured in a fixed coordinate setup and the free motion acceleration data were recorded in floating-coordinate tests. Results suggest the mean surging forces are similar for three models, but the mean pitching moments are different due to different floating platform designs. Dynamic loadings are significant for all force/moment components except for the yawing moment. Frequency domain analysis suggests dynamic loadings are dominated by the fundamental rotational frequency and its third harmonic. Despite of these common characteristics, three floating VAWT models show significantly different dynamic loadings and free motion accelerations under the same wind excitation. Due to scaling limitations, the dynamic motion and force data obtained in the present study could not be directly used for full-scale applications. However, the test result reveals the characteristics of fluid-structural interaction of three potential floating VAWT designs, and experimental data could provide validation benchmarks for future reduced-scale computational modeling