Bubble curtains for noise mitigation: one vs. two

TL;DR

This study compares single and double bubble curtains for noise mitigation, demonstrating that splitting airflow into two curtains enhances acoustic performance and maintains reflective properties, leading to up to 11dB increased insertion loss.

Contribution

It provides experimental and numerical evidence that splitting airflow into two bubble curtains improves noise reduction effectiveness compared to a single curtain.

Findings

Splitting airflow increases insertion loss by up to 11dB.

Reflective properties are maintained when airflow is split.

Equivalent fluid models improve with a gap near the manifold.

Abstract

Bubble curtains are widely used to protect marine life from exposure to noise during offshore construction. However, operating a bubble curtain is costly. Therefore optimizing the acoustic effect of the available air is important. An interesting approach is to split the airflow rate into two separate bubble curtains, rather than one single curtain. This concept is tested experimentally and numerically. The experiments and the model show an increase in performance of the compressed air when it is split between two manifolds. An increased insertion loss of up to 11dB is measured. This increase in performance is possibly due to the fact that the reflective properties of the bubble curtains are maintained when halving the airflow rate. In effect, by splitting the airflow a second acoustic barrier is added. Additionally, the variations in the bubble curtain performance between individual measurements are shown to be largely caused by temporal variations in the air distribution. The applicability of equivalent fluid models for bubble curtains is discussed, and it is shown that accounting for a gap in the bubble curtain, close to the manifold where the bubble curtain is not fully developed, results in better agreement between the modelled and the measured insertion loss.