Technique to Measure Breathing Wave Speeds Using End Point Excitation

摘要

The breathing (or bulge) wave that is caused by interaction of the hose wall andthe fill fluid in a towed array is energy traveling down the array at a nearly constant speed. At sea, the principal origin of the bulge wave is excitation by the turbulent boundary layer. In the laboratory, the bulge wave can be generated by end point excitation of the array. The end of the array is vibrated, which excites a bulge wave at the end shell and at other locations in the array where hose-filling objects are present. The bulge wave amplitude is attenuated by the array hosewall and generally consists of only traveling wave energy. This report describes a simple method to measure the breathing wave speed in a towed array. The array is subjected to end point excitation, and a transfer function between a hydrophone channel and an accelerometer is measured. The local minimum associated with the first breathing wave null across the hydrophone channel is identified. Because both the length of the hydrophone channel and the frequency at which the null occurs are known, the breathing wave speed can be calculated. This method can be implemented at the Axial Vibration Test Facility of the Naval Underwater Systems Center, New London, CT.