Combined CFD and Vibro-Acoustic Approach for Modelling the Underwater Noise Reduction of Bubble Curtains

Worldwide environmental and regulatory concerns on underwater noise emission from offshore pile driving motivate research towards mitigation solutions. Among those systems, air bubble curtains perform well but present challenges for modelling the acoustic performance, or noise reduction. An engineering approach is suggested to assess sound insertion loss of different curtain configurations. The technique is based on the observation that impedance mismatch is the governing loss mechanism, i.e. attenuation increases with air volume in the curtain. A bubbly water region is implemented in a well-established vibro-acoustic Finite Element model for piling noise. The distribution of bubbles is achieved using a Latin Hypercube Sample generator. The bubble properties (density, sound speed, size) and curtain data (air fraction and geometry profiles) are computed by means of a multiphase Computational Fluid Dynamics (CFD) analysis. The latter is established based on technical input from bubble curtain suppliers, combined with environmental input data. The prediction model is at an early development stage. The tendencies of the prediction results seem promising. The model remains to be tested against real-world measurements. Potentially, the suggested model approach may be expanded to evaluate the curtain performance under varying weather conditions, such as sea currents.