Measurements of underwater sound radiated from an offshore wind turbine

Abstract

Underwater acoustic and geophysical systems were deployed to monitor the operation of the Block Island Wind Farm (BIWF). The BIWF consists of five GE Haliade 150-6MW wind turbines each with 150 m diameter blades. The five wind turbines were laid out about 1 km apart in a southwest-to-northeast arc. Each turbine is equipped with a direct drive permanent magnet generator, with no gearbox coupled to the generator. These turbines are variable speed and have independent pitch control by blade. The equipment used to monitor the BIWF operation consisted of a towed array of eight hydrophones, two VLAs with four hydrophones each and a fixed sensor package for measuring particle velocity. This sensor package consists of a three-axis geophone on the seabed and a tetrahedral array of four hydrophones at 1 m from the bottom. Additionally, an acoustic vector sensor was deployed in mid-water. During operations in December 2016, an acoustic signal was detected by the tetrahedral array of hydrophones at a position 50 meters west of the southwestern-most turbine. The frequency of this signal was approximately 72 Hz and the rms sound pressure level was about 100 dB re 1 micropascal. [Work supported by Bureau of Ocean Energy Management (BOEM).]