Underwater noise reduction of offshore wind turbine using compact circular liner

A lined layer used for suppressing the underwater noise radiation from the offshore wind turbine is developed in this study. The lined layer is made from nitrile rubber. It contains periodically distributed axial cavities and each of which consists of a circular truncated cone and a cylinder. The acoustic performance of the lined layer is analysed using the equivalent medium method and the transfer matrix method. Based on the analytical prediction model, an optimal configuration targeting for low-frequency range is designed and its absorption coefficient under 2500 Hz is up to 0.96. The finite element method is employed to examine effects of the lined layer on a scaled tower-water model. The presence of the lined layer can lower the sound pressure level by up to 18 dB. Since the sound speed in the lined layer is lower than that in water, the radiation angle of the sound wave front is smaller than that for the baseline model. Practically, this study puts an early effort on underwater noise control of the offshore wind turbine and proposes a feasible solution for that.