ISSN:0001-4966    

DOI:10.1121/1.1910224

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Intensity and Fourier spectra of refracted and of bottom‐reflected acoustic arrivals in the Mediterranean Sea south of Cyprus at ranges between 16 and 20.4 NM (nautical miles) are presented, together with the most probable sound‐velocity profile and the near‐surface temperature structure. The arrival structure and relationship between pulse travel time and range indicate that most of the 100‐ to 800‐cps energy contributing to an arrival travels along paths similar to rays, but we find that, below 600 cps, there are frequency differences in the locations of these paths. The discovery of these frequency differences causes us to withdraw the postulate of scattering advanced in our first paper of this title and replace it with one of diffraction. According to Officer [Introduction to the Theory of Sound Transmission, McGraw‐Hill Book Co., Inc., New York, 1958), Chap. 2], such differences can be caused by diffraction occurring at depths where the absolute value |λ0(δc′/c)| of the ratio of the fractional change δc′, in the velocity gradient over a wavelength, to the velocity gradientc/λ0is largest. Our results indicate that the diffraction is observable in the convergence zone if |λ0(δc′/c)| at such depths is approximately 5×10−4or greater.

ISSN:0001-4966    

DOI:10.1121/1.1910226

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Acoustic measurements in shallow lakes are subject to interference caused by reflections from the lake surface and bottom. This interference is particularly serious at frequencies below about 2 kHz. If a dipole (two out‐of‐phase simple sources) is used as a projector, substantial sound‐pressure level is available in the near Field, regardless of the well‐known inefficiency of such a projector. At the same time, interference caused by lateral reflection is virtually eliminated by the farfield directivity characteristics of the dipole. The optimum relationships among dipole size, test distance, boundary geometry, and frequency are analyzed and verified by experiment.

ISSN:0001-4966    

DOI:10.1121/1.1910227

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A large, closely packed, steered array is modeled by imposing a traveling wave along the surface of a rectangular radiator. The results in this paper are most pertinent to closely packed arrays made up of elements that are small as compared with a wavelength. For this type of array, it is shown that at large steering angles the cavitation‐limited power is greatly reduced below that achievable at broadside. The cavitation factor is generally less when the beam is steered along the longer side of an array than when the beam is steered across its shorter side. Integral solutions for the nearfield pressure and radiation resistance of a general steered array are presented. Numerical results show that the radiation resistance has a maximum value at a particular steering angle for a specific array, and the nearfield pressures pile up near the leading edge of the array as the beam is steered to a large angle. In the end‐fire case, approximate expressions for the radiation resistance and the nearfield pressure are derived for an infinitely long rectangular strip with beam steering across the width, and for a finite, slender, rectangular array with beam steering along the longer side.

ISSN:0001-4966    

DOI:10.1121/1.1910228

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Volume‐scattering strengths are presented for both daytime and nighttime, measured at three different times, in the same oceanic area during a nine‐month period. The data are analyzed in13‐oct bands covering the frequency region from 2.5 to 20.0 kHz. The maximum and minimum variation in scattering strengths over the nine‐month period range from 11 to 3 dB. Swimbladder volumes of fishes are determined from the acoustic characteristics of deep scattering layers. A volume of 0.72 cm3is computed for fish residing at 950 m and 0.022 cm3for fish at 610 m. Biological sampling of the deep‐scattering layers shows the presence of four families of fishes that possess swimbladders: Myctophidae, Gonostomatidae, Sternoptychidae, and Melamphaidae.

ISSN:0001-4966    

DOI:10.1121/1.1910229

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The stresses that evolve in a thermally shocked liquid were examined. The magnitude and time duration of stress transients generated by aQ‐switched ruby laser were measured in the absence of a phase change and compared with results calculated from a simplified thermodynamic model. It is shown that the model agrees with experimental data over a wide range of incident electromagnetic intensity and for large variations of liquid properties. Results are also presented to show the effect of liquid vaporization on the stress transients and the parameters associated with formation of a gas phase.

ISSN:0001-4966    

DOI:10.1121/1.1910230

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

When a transducer of finite size is used to measure the spectral density of a turbulent sound field, the results are dependent on the size of the transducer. If the transducer is separated from the turbulence by a non‐turbulent medium, or by an elastic layer, then the recorded pressure is a function of both transducer size and layer thickness. Analysis of the effect of transducer size and separating layer is the purpose of this paper. The theory is developed for computation of attenuation of spectral density as a function of transducer size and distance from the turbulent layer.

ISSN:0001-4966    

DOI:10.1121/1.1910231

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

An investigation into the long‐range propagation of sound in shallow, isovelocity water was carried out using an extensive area of the continental shelf off the west coast of New Zealand. The results obtained showed that a classic example of normal‐mode propagation in shallow water was involved. The values of attenuation obtained and the general behavior of the attenuation as a function of frequency are comparable with other shallow‐water areas. Other characteristics of the propagation mechanism can be explained in terms of depth variation and layering of the bottom.

ISSN:0001-4966    

DOI:10.1121/1.1910232

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The theory, design, and operation of a system for the measurement of acoustic impedance at hydrostatic pressures to 10 000 psig are described. The system is a pulse tube featuring the use of coherent pulses. The acoustical characteristics of materials are determined from measurements made on small samples (2 in. diam × ∼ 6 in. long). Three different measurement methods are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910233

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The response and consequent sound radiation of a thin rectangular panel excited by convected boundary‐layer turbulence has been examined. By taking averages over a frequency band, and including many modes in this average, the detailed characteristics of the system are bypassed and only gross features such as panel modal density, ratio of radiation to total resistance, and the boundary‐layer characteristics are of interest. A large portion of the sound power is transmitted in the region of the hydrodynamic coincidence condition. The hydrodynamic coincidence frequency is the most important feature in determining the shape of the transmitted power spectrum, and the power law for the total power radiated. Good agreement between theory, and experiment serve to verify the basic assumptions of the theory.

ISSN:0001-4966    

DOI:10.1121/1.1910234

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP