Grech La Rosa, Andrea; Smith, Tom; Bin Muhammad Ali, Ahmad; (2023) An Experimental Parametric Study on Bubble Screen Performance. In: Proceedings of the 7th Underwater Acoustics Conference & Exhibition (UACE2023). (pp. pp. 675-682). I.A.C.M, Foundation for Research and Technology – Hellas

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Abstract

Offshore engineering activities such as pile driving produce extremely high amplitude noise that is harmful to marine life. To help mitigate the impact of such activities, bubble screens may be used to reduce the acoustic environmental impact. This consists of supplying compressed air through a perforated pipe on the seabed to create a curtain of bubbles. This screen acts as an impedance barrier, preventing transmission of some portion an incident acoustic waves. \n\nThe performance of these designs, as noted in the literature, can be very variable, raising questions around how best to design and operate them. To address this issue, a controlled parametric experiment has been performed in the UCL towing tank. This study has been conducted by supplying a series of individual pipes fastened along a rail across the bottom of the tank with the same pressure applied to each. This setup enables a high degree of flexibility for the bubble screen configuration and ensures a reliable and repeatable performance. An underwater emitter and hydrophone were then used to generate and measure the sound, including the self-noise of the curtain. \n\nInitial studies show positive repeatable results demonstrating how varying parameters such as pressure, mass flow rate, and hole separation influence attenuation performance at a range of frequencies. One configuration was shown to completely eliminate transmission for incident waves above 18kHz. Furthermore, the results show that a high mass flow rate at low pressure yields the most effective results as this generates a more stable bubble screen with a higher void fraction. \n\nFuture studies are planned to consider a broader range of parameters and include environmental conditions such as waves. The noise generating mechanisms of the curtain itself will also be considered with a view to reducing the self-noise.

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