Underwater sound mitigation of bubble curtains with different bubble size distributions

Abstract

Regarding the anchorage of offshore wind turbines' foundations to the sea bed, piling is the best available technology. Without mitigation measures, piling generates sound pressure levels which exceed the limit values for the sound exposure level and the peak level at distance 750 m. In this work, results from acoustical tests on bubble curtains as well as a first attempt for modeling the mitigation effect of bubble curtains are presented and discussed. Finally an outlook to current activities within a new research project is given.The acoustical tests show that a dense bubble curtain consisting of many small bubbles has the best sound mitigation effect. The computer model couldn't be calibrated with the experimental data. The reason might be that in case of very short sound signals the bubbles cannot get into resonance. In order to enhance the computer model, detailed information of the bubble curtain's geometry is needed. Within a new research project, bubble sizes and rising speeds will be measured. Thereby, the air volume fraction and the bubble size distribution will be determined. With this information, the damping properties of bubble curtains will be implemented in a finite element model. © 2012 Acoustical Society of America.