Modeling the noise mitigation of a bubble curtain

The bubble curtain is one of the most used measures to reduce underwater pile driving noise. A model of the local distribution of the effective wavenumber was developed. The bubble size distribution was derived from tank measurements. The local distribution of the air fraction was determined by means of an integral method. In a preliminary step, the transfer characteristics of a bubble curtain were studied. The results show a decrease of the transmission coefficient for higher frequencies and additionally for lower water depths. For lower frequencies, λ/2-transmission can be observed. Examining the noise mitigation of a bubble curtain under offshore conditions, a model of the acoustical scenario was developed. Two different offshore measurement sites are described in detail and compared to the modeling results. The distance between bubble curtain and the pile was identified as an important parameter affecting the noise mitigation. The presented approach shows an appropriate representation of the noise mitigation and allows, due to its generic definition, for future investigations of various aspects, e.g., the influence of the soil or the effect of an extra pile near system on the noise mitigation.