Observation Of Passive Broadband Suppression Of Low-Frequency Underwater Sound
Abstract
We develop a proof-of-principle experiment for a recent theory published by Godin and Baynes, who showed that passive, broadband suppression of underwater sound can occur when a balloon or bladder filled with air is near a low-frequency sound source. The volume of air produces a pressure-release boundary condition that causes scattering, which redirects energy and can destructively interfere with the direct sound from the source. One application of this effect is in Naval vessels, which emit low-frequency sound due to cavitation and vibrations and can thus be acoustically detected. However, it may be that the sound can be significantly reduced with the simple use of a bladder on the hull of the vessel. Experiments with and without a balloon filled with air in the presence of a sound source were conducted in the NPS tank laboratory in Spanagel Hall. Quantitative comparison with the theory indicates agreement, but the results are only rough due to reflections from the surfaces of the water in the tank. We were unable to gate the signal in order to avoid the reflected sound for our experimental parameter values, which were chosen for optimal sound suppression according to the theory. Future experimentation will be conducted in the NPS SLAMR facility, which should be sufficiently deep and wide to allow for the use of gating.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2020
- Accession Number
- AD1127007
Entities
People
- Evan J Mcmellon
Organizations
- Naval Postgraduate School