ASA 124th Meeting New Orleans 1992 October

5pUW12. Bubble density and void fraction measurements in the Gulf of Alaska.

Ming-Yang Su

Naval Res. Lab. Detachment, Stennis Space Center, MS 39529-5004

John Cartmill

Planning Systems, Inc., Slidell, LA 70458

During February--March 1992, several measurements were made of the size density of near-surface bubbles for a radius of 34 to 1200 (mu)m from a depth of 0.25 m down to about 6 m in the Gulf of Alaska by means of a vertical acoustic resonator array. Void fraction measurements were also made at the same time by means of a horizontal array (15 m long) strung along the tether cable for the above acoustic resonator array about 150 m from the R/V. The void fraction was measured by conductivity probes with threshold about 0.2%. The spans between the conductivity probes all located 0.25 m below the water surface are 1, 2, 3, 4, 6, 7, 8, 9, 11, and 15 m, respectively. All the conductivity probes were located 0.25 m below the water surface. The measured bubble density data have been used to compute the corresponding low-frequency (less than 1 kHz) sound speeds. The measured void fraction data have been used to infer the presence and intensity of breaking waves. In this talk some statistical characteristics of these bubble densities, low-frequency sound speeds, and breaking wave statistics are presented. A comparison of these with some previous measurements using the same technique at different field locations shall also be made. [Work supported by ONR Acoustical Reverberation SRP.]