Experimental Study on the Dynamic Responses of a Novel 10 MW Floating Offshore Wind Turbine Integrated With a Fish Cage

Abstract This experimental work is to study the dynamic responses of a novel floating offshore wind turbine integrated with a fish cage (FOWT-FC) under wave and wind loads and to provide a benchmark for the establishment of numerical simulations. A series of model tests of scale 1:30 have been carried out in the ocean basin at Tsinghua Shenzhen International Graduate School (SIGS). This paper provides a detailed description of the experimental setup, including the design, fabrication, calibration and identification of the model, type and arrangement of the sensors. The 6 degrees of freedom (DOFs) displacements of cage, the accelerations at tower top and base and other responses are collected and analyzed. The displacement response amplitude operators (RAOs) are obtained through white noise wave tests, manifesting the excellent seakeeping performance of FOWT-FC. Besides, all responses in the operational and non-operational load cases are below the code limits. A group of controlled experiments are set up to investigate the effect of wind on dynamic responses, and several findings are discovered. In general, wind loads increase low-frequency responses, but have little effect on wave-frequency responses. Moreover, the low-frequency growths under turbulent wind are more significant than those under steady wind. Besides, the turbulent wind enhances the high-frequency responses at around tower’s 1st-mode vibration frequency. Whether under the action of random waves alone or combined wave-wind, the cage’s motions are predominantly controlled by low-frequency and wave-frequency responses, while hardly influenced by high-frequency excitations. The blades’ 3P excitation is not observed in the cage motion spectra, but found in the tower acceleration spectra. Also interestingly, the tower top acceleration has more pronounced spectral contents at high frequencies than the tower base acceleration does. On the contrary, the tower base acceleration has more pronounced spectral contents at low frequencies than the tower top acceleration does. These low frequencies are sourced from the wind loads and difference-frequency hydrodynamic loads.