Mitigating underwater noise from offshore wind turbines via individual pitch control

This paper proposes a pitch control strategy to mitigate the underwater acoustic footprint of offshore wind turbines, a measure that will soon become necessary to minimize impacts on marine life, which rely on sound for communication, navigation, and survival. First, we quantify the underwater acoustic signature of blade-generated aerodynamic noise from three reference offshore wind turbines-the NREL 5 MW, DTU 10 MW, and IEA 22 MW using coupling blade element momentum and coupled air-water acoustic propagation modeling. Second, we propose and implement an open-loop individual pitch control (IPC) strategy that modulates the pitch of the blade at the blade passing frequency to attenuate the overall sound pressure level (OSPL) and the amplitude modulation (AM) of the transmitted underwater noise. Third, we benchmark IPC performance against conventional pitch schemes. The results indicate that up to 3 dB reductions in OSPL and a decrease in AM depth of 20% can be achieved with a pitch variation Delta theta approximate to 3 degrees, with limited losses (3-5%) in energy capture. Additionally, we show that the pitch-based noise mitigation strategy predominantly benefits low-and mid-frequency ranges, with limited effectiveness for high-frequency-hearing species. These findings highlight a previously underappreciated noise pathway and demonstrate that targeted blade-pitch modulation can mitigate offshore wind turbine underwater noise impact.