External Acoustic Black Holes to reduce structural vibration and radiated sound by a plate in contact with water

Ship noise arises from various sources, including propeller cavitation, hydrodynamic flow, and onboard machinery. Vibrations from rotating and reciprocating machines can propagate through the ship's structure and radiate into the marine environment, significantly contributing to underwater noise pollution. This study investigates the potential of Acoustic Black Holes (ABH) to mitigate structural vibrations and, consequently, reduce underwater radiated noise. ABHs are passive vibration-damping devices that utilize a unique mechanism to concentrate and dissipate vibrational energy. While their potential on structures in air is recognized, the effect on structures in contact with water has yet to be investigated. A series of experiments was conducted on a rectangular steel plate subjected to controlled excitation using an electrodynamic shaker. The results show a noticeable reduction in structural vibration levels across a broad frequency range (50–5000 Hz) with the implementation of ABHs. However, this reduction does not directly translate into a corresponding decrease in underwater radiated noise. The inconsistency between vibration reduction and acoustic radiation was analysed and discussed. These findings provide insight into the effectiveness and limitations of ABHs in underwater noise mitigation strategies.