摘要:

A new analytical method is introduced for the study of the sound radiation and reflection from the open end of a duct. The sound is thought of as an aggregation of the quasiparticles—phonons. The motion of the latter is described in terms of the statistical distribution, which is derived from the classical wave theory. The results are in good agreement with the solutions obtained using the Wiener–Hopf technique when the latter is applicable, but the new method is simple and provides straightforward physical interpretation of the problem. Furthermore, it is applicable to a problem involving a duct in which modes are difficult to determine or cannot be defined at all, whereas the Wiener–Hopf technique is not.

ISSN:0001-4966    

DOI:10.1121/1.382921

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Ultrasonic reflectivity from a solid is a function of longitudinal‐ and shear‐wave velocities and attenuations, as well as the density. Using stress‐dependent acoustic velocities obtained from second‐order elasticity theory, we have calculated the plane‐wave reflectivity at and near the Rayleigh critical angle for uniaxial stress. Reflectivity amplitude and phase results were obtained for both tensile and compressive stress. From the reflectivity amplitude data, values of Raleigh‐wave velocity versus stress were obtained. The results exhibit the expected behavior and a comparison with such experimental data as are available shows fair agreement.

ISSN:0001-4966    

DOI:10.1121/1.382922

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The formulation of scattering of low‐frequency acoustic radiation in an anisotropic random medium, like the ocean, results in an integro‐differential equation for the coherence function. It was argued, however, that for horizontal scattering a more simplified differential equation is adequate. In this paper we demonstrate, by direct numerical calculation, that for a realistic case, this simplification is indeed appropriate and that the errors introduced are only of the order of a few percent. For vertical scattering in the absence of refraction, it is pointed out that a quasiasymptotic angular distribution results for large propagation distances in contrast to the exact asymptotic state that is predicted by the differential equation.

ISSN:0001-4966    

DOI:10.1121/1.382923

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Sound speed in liquids is calculated in terms of Mie potential parameters with the assumption that the intermolecular potential energy is the dominant factor. Using this simple model, it is shown that Beyer’s parameter of nonlinearity, Rao’s exponent, and the Gruneisen parameter are all simply related to each other. Liquids obey a law of corresponding states in terms of reduced variablesc2/U0andV/V0, wherecis sound speed,U0is the heat of vaporization,Vis specific volume, andV0specific volume at absolute zero temperature. To a first approximation, the parameter of nonlinearity is shown to be a linear function of reciprocal sound speed, and the calculated results are in reasonably good agreement with the empirical result noted by Ballou.

ISSN:0001-4966    

DOI:10.1121/1.382924

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Recent theoretical and experimental advances have produced an accurate model of the power spectrum of temperature fluctuations in turbulent air. This model temperature spectrum and a semiempirical energy spectrum are used to predict the shape of the acoustic scattering cross section as a function of wavenumber and scattering angle. Experiments have shown that the temperature spectrum in air has a ’’bump’’ at high wavenumbers, and the model temperature spectrum shows that this feature is expected theoretically. A corresponding bump is predicted to appear in the acoustic scattering cross section. The bump in the cross section is reduced if velocity fluctuations dominate the scattering, because the energy spectrum has no bump. For typical energy dissipation rates in the atmospheric boundary layer, a 2‐kHz acoustic sounder senses scattering attributable to the bump in the cross section. The amount of scattering attributable to the bump depends on the acoustic wavenumber and the microscale, and can be as much as 50% greater than the scattering predicted by the usual theoretical interpretation.

ISSN:0001-4966    

DOI:10.1121/1.382925

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

It is shown that the technique of measuring acoustic intensity by means of the cross correlation between nearby microphones cannot, in general, be extended to situations in which there is mean flow. However, it may be possible to apply this technique to measure intensities in ducts with mean flow, at frequencies below their cutoff frequency.

ISSN:0001-4966    

DOI:10.1121/1.382926

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A circular flow tank facility has been developed which features extremely low acoustic and vibration ambient conditions. This facility is described, operating procedures associated with its use are presented, and limitations in the measurement procedures are mentioned. The flow facility has been used to measure the noise output of pressure and pressure gradient hydrophones during actual flow conditions and results of these tests are presented and discussed.

ISSN:0001-4966    

DOI:10.1121/1.382927

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The acoustic scattering properties of spherical gas bubbles in a liquid differ from those of a pressure‐release sphere by the well‐known ’’giant’’ monopole resonance at very low frequencies, which is due to the compressibility of the gas contained in the bubble. We show here that, in addition to this monopole resonance, a large number of higher‐frequency resonances exist which are either overtones of the monopole, or which correspond to both fundamental and overtones of bubble vibrations of higher multipolarity. Although much smaller in size than the giant monopole, these resonances may nevertheless constitute features of some importance in sound scattering from gas bubbles.

ISSN:0001-4966    

DOI:10.1121/1.382928

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

For a Pekeris model the contribution of the continuous mode integral is analyzed in terms of virtual modes with particular attention to cases with a discrete mode just below or just above cutoff. There is a steady change of amplitude as a virtual mode changes into a discrete mode. The mode amplitudes decay with range and analytic approximations valid in most practical situations are obtained.

ISSN:0001-4966    

DOI:10.1121/1.382929

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Numerous experiments suggest that bubble formation in water is initiated by preexisting gas nuclei. This is unexpected since gas phases larger than the order of 1 μm in radius ought to rise to the surface of a standing liquid, whereas smaller ones should dissolve rapidly via the outward diffusion of gas that results from surface tension. Several mechanisms for stabilizing gas nuclei have been proposed, but in each case there is experimental evidence to the contrary. In this article, a model is investigated in which stability is maintained by surface‐active skins of varying gas permeability. Data on ultrasonic cavitation and on bubble formation by counter‐diffusion indicate that such skins, if they exist, must be initially permeable. Quantitative comparisons with bubble counts obtained recently from supersaturated gelatin lead to the further conclusion that nuclear skins become effectively impermeable if the static pressure is raised rapidly by a sufficiently large amount. The surface area, length, and energy per skin molecule deduced from these comparisons are remarkably similar to those of known surfactants, such as lung extract, lecithin, and oleyl alcohol.

ISSN:0001-4966    

DOI:10.1121/1.382930

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP