摘要:

Pair correlations and the effects of dense packing are included to extend existing results on reflection and scattering by distributions of protuberances (bosses) on rigid or free base planes. The earlier energy conserving forms for the specularly reflected wave, the surface impedance, and the differential scattering cross section per unit area, are obtained in terms of a transform of the scattering amplitude of an isolated boss. Low‐frequency approximations are developed with emphasis on the roles of the packing density and multipole coupling effects, and explicit results are given for semi‐elliptic cylinders and hemi‐ellipsoids. For lossless bosses, the reflection coefficient has a minimum, and the incoherent scattering a maximum, at the packing density corresponding to maximum fluctuations in the number of bosses per unit area. Multipole coupling effects may be misinterpreted in data inversion programs as changes in boss shape; if such effects are not included, then, e.g., hemispheres may be mistaken for hemiellipsoids broadened along the base plane and shortened along the normal.

ISSN:0001-4966    

DOI:10.1121/1.388726

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Published and unpublished data on sound pressure distributions about the human head and torso were collected and analyzed. The results of the analysis are presented graphically. The data include measurements on both humans and manikins in both progressive wave and diffuse fields. The results can be used to aid selection of locations for the microphones of noise dosimeters and hearing aids and design of spectrum shaping circuits for these microphones. An appendix discusses procedures for determining whether it is appropriate to assume a progressive wave or diffuse field when these data are applied to actual situations in the field.

ISSN:0001-4966    

DOI:10.1121/1.388727

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Sound‐speed properties of liquids are calculated in terms of the easily measurable parameters on the assumption that the isochoric temperature derivative of the sound speed is the dominant factor with significant contribution to influencing the thermo‐acoustic properties. Using this simple model it is shown that Beyer’s parameter of nonlinearity, Rao’s exponent, Carnevale and Litovitz’s exponent, molecular constant relating internal pressure and cohesive energy density, the microscopic Grüneisen parameter, and the thermodynamic or pseudo‐Grüneisen parameter are all simply related to each other. The parameter of nonlinearity has been shown to depend on both Rao’s exponent and that of Carnevale and Litovitz. The calculated results are in reasonably good agreement with both the empirical and experimental results for various liquids.

ISSN:0001-4966    

DOI:10.1121/1.388842

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A compound modulated whistle source has been developed which produces broadband sound of high intensity in air over the 16 to 160‐kHz frequency range. The development and characteristics of a prototype whistle source are described, and the details given of the final whistle design. A compound source of three such whistles is shown to have an adjustable frequency spectrum, of particular application to modeling experiments.

ISSN:0001-4966    

DOI:10.1121/1.388843

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Gas bubbles that are driven into oscillation within a liquid pulsate with amplitudes that are determined largely by the thermodynamic behavior of the gas contained within the bubble. Theoretical approaches to the solution of the motion of the radius of the bubble normally involve the polytropic exponent of the gas. Measurements are presented of this exponent for three different gases and for a wide range of values of the exponent. Comparison with available theories indicates good agreeement between measurements and predictions provided the gas bubble is not driven near one of its harmonic resonances.

ISSN:0001-4966    

DOI:10.1121/1.388844

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Measurements are presented in this paper of the pulsation amplitude of an individual air bubble that is levitated in a glycerine–water mixture by a stationary acoustic wave operating at a frequency of 22.2 kHz. Observations of the bubble pulsation for a wide range of bubble sizes demonstrate the existence of then=2 harmonic resonance (ω≊ω0/2). The available theoretical information on linear and nonlinear bubble oscillations is adapted to apply to the specific experimental conditions. Comparisons made with the theory show excellent agreement between measurements and predictions.

ISSN:0001-4966    

DOI:10.1121/1.388845

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The paper deals with the radiation of aerodynamic sound due to two symmetrically placed point sources on either side of a double layer jet flow. These sources are regarded as the driving forces in the acoustic medium. In consequence, the illumination due to a point source on one side is supplemented by the transmission due to the point source on the other side, which results in an enhanced radiation on each side. The analysis provides an expression for the reflexion coefficient which is valid at an interface that separates a fluid at rest from a fluid in motion [which is in perfect agreement with the one obtained by Miles, J. Acoust. Soc. Am.29, 226–228 (1957), Ffowcs Williams, J. Fluid Mech.66, 791–816 (1974), and Dash, J. Sound Vib.49, 365–377; 379–392 (1976)] and predicts an aerodynamic zone of silence, also known as the valley of relative silence, which prevails parallel to the vortex interface off the source locations and appears in the form of sharp clefts around the jet axis. This deep valley in the directivity pattern deepens as the jet velocity or the ambient‐to‐jet density ratio ( ρ0/ρ1) increases. Marked by the conspicuous absence of highly directional beams, the formation of symmetric directivity patterns around the jet axis resembling a kidney‐shaped, lung‐shaped, or heart‐shaped structure has been vividly illustrated in Figs. 5–8. The emergence of these structures depends on the jet speed and the ambient‐to‐jet density ratio ( ρ0/ρ1). This investigation also suggests that the sharp, steep, dual dimples formed in the directivity pattern are characteristics to the transonic and supersonic flows at ρ0/ρ1=1 whereas the balloon‐type, puffed‐up, dual loops formed symmetrically at close angles to the jet axis in the forward flow direction are solely characteristics to the supersonic flows at all values of the ambient‐to‐jet density ratio, ρ0/ρ1≥1.

ISSN:0001-4966    

DOI:10.1121/1.388846

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The propagator matrix formalism of F. Gilbert and G. E. Backus is a convenient general method for treating stratified media. In this paper, the Gilbert–Backus formalism is used in conjunction with Sylvester’s matrix theorem to obtain an exact solution for wave propagation in a periodically stratified medium of arbitrary thickness. Explicit expressions are derived for the simple case of a periodically layered fluid. These expressions are used to investigate several interesting limiting cases. Application of the method to the more complicated case of a periodically layered solid is briefly discussed.

ISSN:0001-4966    

DOI:10.1121/1.388847

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The acoustic propagation losses between a 230‐Hz cw source and a multi‐hydrophone receiving system were measured over Dickins Seamount in the Northeast Pacific. The source was towed at depths of 18 and 184 m. The receiving system had hydrophones spaced in depth from 323 to 633 m. The measurements were made to a maximum range of 130 km with the receiver located at a range of 60 km from the seamount peak. The results show that the seamount cast an acoustic shadow over the receiver, increasing the propagation loss by up to 15 dB, when the source was shallow and in a position which enabled the seamount to intercept all of the deep refracted source energy. Back reflections from the seamount with levels 6 to 13 dB below the direct signal level were present when the shallow source was 3 to 5 km from the seamount peak. Downslope reflections enhanced the direct signal by up to 10 dB when the shallow source was within 3 km of the peak. Acoustic shadowing and reflection effects were minimal in the results for the deep source because most of the source energy propagated along the sound‐channel axis above the seamount peak. The analysis indicates that ray theory is adequate for describing the reflection effects of the acoustic propagation but does not account for all of the acoustic energy in the shadow zone.

ISSN:0001-4966    

DOI:10.1121/1.388849

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

This paper derives and illustrates the utility of the derivative of a determinant that arises from the solution of the wave equation in a multi‐layered medium. The horizontal wavenumbers at which the determinant is zero are the eigenvalues of the solution. The derivative of the determinant with respect to the horizontal wavenumber therefore can be an aid in finding the roots (zeros). More importantly, the eigenfunction normalization constant is shown to be a function of this derivative. Two types of boundary are discussed, an impedance boundary and an infinite half‐space. The normalization using the derivative of the determinant is shown to apply to both types. The derivative of the determinant is also useful in evaluating mode group velocities. An algorithm for the efficient determination of the derivative of a determinant is given. This algorithm includes a rapid computational technique that applies special properties of matrix operations and utilizes the sparseness of the determinant.

ISSN:0001-4966    

DOI:10.1121/1.388850

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP