LOW-FREQUENCY ACOUSTIC EMISSIONS IN FRESH AND SALT-WATER

The impact of a jet of water onto a still water surface results in the entrainment of large amounts of air and the eventual formation of a b ubble plume. Densely populated bubble plumes are generated by dropping a fixed volume of water, held in a cylindrical container; onto a stil l-water surface. The detached bubble plume, which is roughly spherical in shape, then undergoes volume pulsation and radiates relatively lar ge-amplitude, low-frequency sound. The results of a laboratory study o f the noise produced by this process were reported previously by Kolai ni et al. [J. Acoust. Soc. Am, 94, 2809-2820 (1993)]. In this paper we report the results of a field study of noise produced by this process in both fresh water (Lake Washington, WA) and salt water (Puget Sound , WA). Studies of acoustic emissions from transient bubble plumes as a function of cylinder parameters are described, with specific attentio n devoted to a comparison of the results obtained in salt and fresh wa ter. The measurements, which exhibit good agreement with laboratory st udy, indicate that there is a correlation between the acoustic intensi ty radiated from bubble plumes and the total potential energy of the w ater jet.