During installation of monopiles and jackets at sea, the noise generated by high-energy piling may harm the marine environment. To mitigate the risk of noise for marine life, governments have adopted noise limits for pile-driving operations in their permits for offshore construction projects. Air bubble curtains reduce the sound-levels. A looped hose on the seabed - pressurized by air compressors – generates the bubble curtain. Currently, engineers base the bubble curtain designs on previous experience and not on scientific research. Companies experience large variations in the current performance of bubble curtains. A better understanding of the noise generation and mitigation mechanisms would enable better engineering of the bubble curtains, leading to screens that are more effective and to lower costs. Improved screens will control better the noise levels and will reduce the risk not to comply with the specific noise requirements per piling project.
Bubbles JIP will contribute to more efficient and effective designs of bubble curtains to reduce noise during offshore installation. This project researches the current practice of bubble curtain generation. It will also research the sound propagation of piling noise through water and soil and the physical mechanism of noise attenuation by air bubbles. We will develop technology to measure the bubble size distribution and concentration over the water depth, also in relation to waves and current.
Based on this improved knowledge and understanding we will develop a computer model to calculate the effect of improved configurations of air bubble curtain on the noise levels during offshore installation. For an efficient application of the knowledge gained within this project, we will develop guidelines for the design of bubble curtains, which we will report in a “Best Practice” reference document, providing:
The project partners will benefit from the improved understanding of the working principles and performance dependencies of noise mitigation by a bubble curtain. It will also allow making a more accurate budget and schedule estimates for wind farm installation.
This project is supported by the Netherlands Enterprise Agency and TKI Wind op Zee.