Measurement of the nearfield intensity of vibrating ribbed plates by underwater nearfield imaging

Abstract

The vibration of a free plate submerged in an acoustic medium is investigated analytically and experimentally. The plate's vibration and the resulting acoustic field were analyzed by finite element method, resulting in the prediction of the resonances and the surface pressure and intensity for three submerged plates: one without ribs, one with one rib, and one with two unequal ribs. In the measurement, the ARL System for Underwater Nearfield Imaging (SUNI) was used to record an acoustic pressure hologram within the nearfield of each plate with the plate being excited by a shaker at specified locations. The recorded hologram was then digitally processed to calculate and display the plate's surface pressure, velocity, and acoustic intensity as well as the acoustic intensity map within a wavelength of the plate's surface. The farfield directivity of the acoustic radiation of the plate was also obtained. [Work supported by the Ship Acoustic Department of the DTNSRDC/Carderock.]