Offshore Piling Noise Attenuation: Theory and new Applications on Monopiles and Jacket Foundations

For the protection of marine animals in Germany, the acoustic underwater noise from pile driving at offshore wind farms is required to be less than 160 dB (SEL) at a distance of 750 m. In practice the use of soundproofing systems is necessary in Germany. Piling noise is radiated from the pile surface directly into the water and deeper into the soil as travelling waves. These waves can interact with the water and induce additional underwater noise in larger distances. Underwater noise in the far field is usually reduced by bubble curtains. For the special near field conditions and noise radiation a very effective noise mitigation method is developed. It uses small elastic elements of different sizes and materials arranged around a pile to produce reflections, scattering and material damping effects with resonant vibrations. This leads to controllable effective underwater noise reductions in the near field of radiated piling noise. The effectiveness of the different elements was investigated in laboratory tests and under offshore conditions. Two offshore wind farms with monopile foundations were installed by realizing these near field damping elements in combination with far field big bubble curtains, resulting in noise mitigations of up to 25 dB (SEL@750m).