Effect of surface ship internal fluid containers on external acoustic intensity measurements
Smith, Amy Ruth
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The nearfield acoustic intensity resulting from vibration transmitted from a main machinery foundation through supporting structure and fluid containing tanks into the hull structure, and then into the surrounding fluid has been studied for a scale model of a frigate ship. The scale model is 1:10 and the scaled frequency range is 640 Hz to 15 kHz. Acoustic pressure is measured on adjacent cylindrical contours close to the surface of the underwater vibrating surface with the fluid-containing tank first empty and the full. The time-averaged acoustic intensity is then calculated from the pressure cross-spectrum. The resulting sound intensity patterns over the surface of the vibrating structure are studied obtain an insight as to which parts of the structure are primarily responsible for the radiated noise. The spatial characteristics of the acoustic intensity patterns are indicators of the energy exchange between the structure and the acoustic medium. Additionally, the total radiated power has been calculated from the local acoustic intensity measurements and these experimental results have been compared with sound radiation measurements from a comparable model of scale 1:6.25.
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