Project in the Spotlight TKI Wind op Zee: Noise Mitigation System

Reducing noise during offshore pile driving is essential for underwater life, especially for porpoises, seals and other marine wildlife. These animals need their sonar system for all their activities from navigation, mating to finding food. Worst case scenario is that, if too much noise is produced, their sonar systems deteriorate, and they will not be able to navigate and find their food.

The Dutch standard for noise emission at sea depends on the season, e.g. mating or birthing season, in which pile driving takes place and of the size of the wind farm. The average standard is 168 dB. One of the successful new technologies to reduce underwater noise is the Noise Mitigation System. When used in combination with another noise reduction system, the Big Bubble Curtain, the Noise Mitigation System meets the Dutch standard.

The Noise Mitigation System is developed by Van Oord, AdBm Technologies and TNO, with support of TKI Wind op Zee and RVO. The system uses special acoustic resonators that target the frequencies in which most of the piling energy is emitted. Piling energy typically peaks at very low frequencies. The other method, the Big Bubble Curtain, targets the higher frequencies. Together they mute the frequencies that disturb marine life.

The Noise Mitigation System works with the same principle as the muffler in the exhaust of a car. The resonators, which, in the Noise Mitigation System, look like inversed coffee cups, are mounted in a frame that folds in and out, like window blinds. During pile driving the frame, which is light and robust at the same time, is folded out around the pile, from the surface of the water to the seabed. The resonators in it absorb the high-energy frequencies.

After six years of developing, testing and demonstration, the first commercial use of the Noise Mitigation System took place earlier this year; in the installation of wind farms Borssele III and IV.