EXPERIMENTS IN PASSIVE SUPPRESSION OF LOW-FREQUENCY BROADBAND UNDERWATER SOUND
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Authors
Wyman, Richard L., III
Subjects
underwater sound suppression
Advisors
Denardo, Bruce C.
Godin, Oleg A.
Date of Issue
2021-12
Date
Publisher
Monterey, CA; Naval Postgraduate School
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Abstract
A theoretical article by O. A. Godin and A. B. Baynes in 2018 predicts that an air-filled bladder near an underwater sound source can substantially suppress the sound emission. Practical applications include reducing the acoustic signature of naval vessels by placing a bladder near the propellers. We performed experiments in a Spanagel Hall tank and in Monterey Bay, comparing data to the theory. To improve previous thesis data gathered in the tank, we procured a more suitable sound source and a better bladder, and we increased the mass of the anchor that tethers the bladder, so that a larger bladder could be submerged. In addition, the method of gathering data was improved so that essentially continuous values occurred over our frequency range of 0.5 to 5.0 kHz. Data were gathered with and without the air bladder, and the ratio of the amplitudes were compared to predicted values, yielding positive trends. In Monterey Bay, an imploding lightbulb was used as a source while large balloons were used as a bladder. The bulb was burst at depth 10 meters with and without the balloons, and the sound was measured by a distant receiver. The data were compared to advanced theoretical models, accounting for some aspects of the environment. This initial attempt yielded encouraging results, indicating that the theory should be further tested by more controlled experiments in the ocean environment.
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Thesis
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Distribution Statement
Approved for public release. Distribution is unlimited.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.