Development and Characterization of an Underwater Acoustics Laboratory Via in situ Impedance Boundary Measurements

• Main Author: Vongsawad, Cameron Taylor
• Format: Text
• Language: unknown
• Published: BYU ScholarsArchive 2021
• Subjects: acoustic; anechoic panels; boundary absorption; characterization; deconvolution; finite-impedance boundary; in situ calibration; lab design; normal-mode waveguide modeling; reverberation time; Schroeder frequency; through the sensor; ultrasonic acoustic propagation; underwater acoustics; water tank; Physical Sciences and Mathematics; Orca
• Online Access: https://scholarsarchive.byu.edu/etd/9818; https://scholarsarchive.byu.edu/context/etd/article/10827/viewcontent/7772439622912420190902_etd.pdf

Modeling underwater acoustic propagation comes with a variety of challenges due to the need for proper characterization of the environmental conditions. These conditions include ever changing and complex water properties as well as boundary conditions. The BYU underwater acoustics open-air tank test-bed and measurement chain were developed to study underwater acoustic propagation within a controlled environment. It was also developed to provide ways to test and validate ocean models without the high cost associated with obtaining open ocean measurements. However, tank measurements require additional characterization of boundary conditions associated with the walls of the tank which would not be present in an open ocean. The characterization of BYU's underwater acoustic tank included measuring the calibrated impulse response of the tank through frequency deconvolution of sine swept signals in order to determine the frequency dependent reverberation time through reverse Schroeder integration. The reverberation time allows for calculating the frequency dependent spatially averaged acoustic absorption coefficient of the tank enclosure boundaries. The methods used for this study, common to room acoustics, also yield insights into the Schroeder frequency limit of the tank as well as validate models used for quantifying the speed of sound in the tank. The acoustic characterization was validated alongside predicted values and also applied to a tank lined with anechoic panels in order to improve the potential for modeling the tank as a scaled open ocean environment. An initial investigation into effective tank models evaluated the idealized rigid-wall and pressure-release water-air boundary model, a finite-impedance boundary model applying the measured acoustic boundary absorption and a benchmark open ocean model known as ORCA in order to determine potential tank model candidates. This study demonstrates the efficacy of the methodology for underwater acoustic tank characterization, provides a frequency dependent acoustic ...