Behavioral response studies (BRS) are increasingly being conducted to better understand basic behavioral patterns in marine animals and how underwater sounds, including from human sources, can affect them. These studies are being enabled and enhanced by advances in both acoustic sensing and transmission technologies. In the design of a 5-year project in southern California (“SOCAL-BRS”), the development of a compact, hand-deployable, ship-powered, 15-element vertical line array sound source enabled a fundamental change in overall project configuration from earlier efforts. The reduced size and power requirements of the sound source, which achieved relatively high output levels and directivity characteristics specified in the experimental design, enabled the use of substantially smaller research vessels. This size reduction favored a decentralization of field effort, with greater emphasis on mobile small boat operations capable of covering large areas to locate and tag marine mammals. These changes in configuration directly contributed to significant increases in tagging focal animals and conducting sound exposure experiments. During field experiments, received sound levels on tagged animals of several different species were within specified target ranges, demonstrating the efficacy of these new solutions to challenging field research problems.
Turbulent boundary layer wall-pressure spectra from various experimental investigations and a recent numerical simulation are presented. The spectra are compared in nondimensional form with three commonly used scaling laws. Attenuations resulting from inadequate sensor spatial resolution are shown to be of primary importance at the higher frequencies. The dependence of the scaling laws on momentum thickness Reynolds number is discussed. The ratio of the outer to the inner boundary layer length scale is shown to provide insight into the observed trends in the spectra.
Absfrncl-The securify of faciliries on or nearports and waterwayshas become a &er of nafionnl security The waterways und porfs can be used by intruders to gain quick, close proximity accerS to a facility wifhout alerting the on-sife security force Existing underwater sensois do not adequately meet tke challenge of sensing flre acousfical signals proriuced by a waterborne intruder due to ihe noisy nature of ports and waterways. This paper describes a new vector sensor developed for the Navy's towed array applications fhat meefs ihe ckallenge by virtue of ifs direcfional capabilities.
This paper examines in detail the flow structure and associated wall pressure fluctuations caused by the injection of a round, turbulent jet into a turbulent boundary layer. The velocity ratio, r, ratio of mean jet velocity to the mean cross flow, varies from 0.5 to 2.5 and the Reynolds number based on the cross flow speed and jet diameter is 1.9ϫ10 4 . Particle image velocimetry is used to measure the flow and flush mounted pressure sensors installed at several locations used to determine the wall pressure. The results consist of sample instantaneous flow structures, distributions of mean velocity, vorticity and turbulence intensity, as well as wall pressure spectra. The flow structure depends strongly on the velocity ratio and there are two distinctly different regions. At low velocity ratios, namely rϽ2, a semicylindrical vortical layer ͑''shell''͒ forms behind the jet, enclosing a domain with slow moving reverse flow. The vorticity in this semicylindrical shell originates from the jet shear layer. Conversely, at high velocity ratios, namely rϾ2, the near-wall flow behind the jet resembles a Karman vortex street and the wall-normal vortical structures contain cross flow boundary layer vorticity. Autospectra of the pressure signals show that the effect of the jet is mainly in the 15-100 Hz range. At rϽ2, the wall pressure fluctuation levels increase with r. At rϾ2, the wall pressure levels reach a plateau demonstrating the diminishing effect of the jet on the near-wall flow. Consistent with the flow structure, the highest wall pressure fluctuations occur off the jet centerline for rϽ2 and along the jet centerline for rϾ2. Also, the advection speed of near-wall vortical structures increase with r at rϽ2, while at rϾ2 it is a constant.
Due to civilian noise complaints and damage claims, there is a need to establish an accurate record of impulse noise generated at military installations. Current noise monitoring systems are susceptible to false positive detection of impulse events due to wind noise. In order to analyze the characteristics of noise events, multiple channel data methods were investigated. A microphone array was used to collect four channel data of military impulse noise and wind noise. These data were then analyzed using cross-correlation functions to characterize the input waveforms. Four different analyses of microphone array data are presented. A new value, the min peak correlation coefficient, is defined as a measure of the likelihood that a given waveform originated from a correlated noise source. Using a sound source localization technique, the angle of incidence of the noise source can be calculated. A method was also developed to combine the four individual microphone channels into one. This method aimed to preserve the correlated part of the overall signal, while minimizing the effects of uncorrelated noise, such as wind. Lastly, a statistical method called the acoustic likelihood test is presented as a method of determining if a signal is correlated or not.
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