摘要:

A self‐consistent method of estimating effective macroscopic elastic constants for inhomogeneous materials with spherical inclusions is formulated based on elastic‐wave scattering theory. The method for general ellipsoidal inclusions will be presented in the second part of this series. The case of spherical inclusions is particularly simple and therefore provides an elementary introduction to the general method. The self‐consistent effective medium is determined by requiring the scattered, long‐wavelength displacement field to vanish on the average. The resulting formulas are simpler to apply than previous self‐consistent scattering theories due to the reduction from tensor to vector equations. In the limit of long wavelengths, our results for spherical inclusions agree with statically derived self‐consistent moduli of Hill and Budiansky. Our self‐consistent formulas are also compared both to the estimates of Kuster and Toksöz and to the rigorous Hashin–Shtrikman bounds. (For spherical inclusions and long wavelengths, the Kuster–Toksöz effective moduli are known to be identical to the Haskin–Shtrikman bounds.) A result of Hill for two‐phase composites is generalized by proving that the self‐consistent effective moduli always lie between the Haskin–Shtrikman bounds forn‐phase composites. Numerical examples for a two‐phase medium with viscous fluid and solid constituents show that the real part of our self‐consistent moduli always lie between the rigorous bounds, in agreement with the analytical results. Some of the practical details in the numerical solution of the coupled, nonlinear self‐consistency equations are discussed. Examples of velocities and attenuation coefficients estimated when the solid constituent possesses intrinsic absorption are also presented.

ISSN:0001-4966    

DOI:10.1121/1.385171

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A self‐consistent method of estimating effective macroscopic elastic constants for inhomogeneous materials with ellipsoidal inclusions is formulated using elastic‐wave scattering theory. The method is a generalization of the method for spherical inclusions presented in the first part of this series. The results are compared to the Kuster–Toksöz estimates for the elastic moduli and to the rigorous Hashin–Shtrikman bounds and Miller bounds. For general ellipsoidal inclusions, our self‐consistent estimates satisfy both the Hashin–Shtrikman bounds and the more stringent Miller bounds, whereas the Kuster–Toksöz estimates for nonspherical inclusions do not satisfy even the Hashin–Shtrikman bounds in general. Our self‐consistency conditions for the cases of needle and disk inclusions differ from those of Wu, Walpole, and Boucher. Since our results are in better agreement with the rigorous bounds, it is concluded that our results are to be preferred. The method is also briefly compared to other self‐consistent scattering theory approaches. The theory is used to calculate velocity and attenuation of elastic waves in fluid‐saturated media with oblate and prolate spheroidal inclusions.

ISSN:0001-4966    

DOI:10.1121/1.385172

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Expressions are derived for the scattered farfield pressure which results from the illumination of an infinite aluminum cylinder by a plane acoustic wave, whose propagation direction makes an arbitrary angle, α, with the normal to the cylinder axis. Computations are made at angles between α=0 ° and the Rayleigh critical angle, α=31.3 °. Changes in the scattered field are related to shifts in the paths of geometric and elastic surface waves from circumferential at α=0 °, to helical, to axial Rayleigh surface waves generated at the Rayleigh critical angle.

ISSN:0001-4966    

DOI:10.1121/1.385173

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The wave motion generated by a time‐harmonic buried line force in a solid with a stress‐free, periodic surface is investigated. The problem is formulated in terms of a spectral type of representation for the total particle displacement on the boundary. Numerical results are presented for the sinusoidal boundary. The computations have been carried out for four different heights of the periodic profile (the plane boundary included), a single value of the Poisson ratio, a single frequency of operation, two different orientations of the line force and two different locations of it.

ISSN:0001-4966    

DOI:10.1121/1.385174

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

TheR‐matrix formalism of nuclear reaction theory is applied to the classical problem of wave scattering by an obstacle, as exemplified by acoustic scattering from fluid spheres imbedded in another fluid. The modal mechanical impedance of the system is a meromorphic function of the WignerRtype, which may be represented by a Mittag–Leffler series exhibiting its poles. The scattering functionSn(a diagonalSmatrix) is represented in anexactfashion byR, and in the one‐level approximation it reduces to the analytic function we obtained in our previous studies, with resonance‐level shifts and widths introduced by theR‐matrix formalism. Absorption in the obstacle or in the medium causes further shifts and broadening of the widths. Graphs of theRfunction and of the modal resonances as found from various level approximations are displayed and discussed.

ISSN:0001-4966    

DOI:10.1121/1.385175

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An analysis has been carried out to evaluate the sound radiation from a finite length unflanged, hard walled circular duct with uniform axial flow, both inside and outside the duct, using the Wiener–Hopf technique (in particular, Jones’ method). The theory developed includes many of the earlier results for the semi‐infinite length duct carried out by other authors, in particular, Lansing, Carrier, and Vajnstejn, in the appropriate limit. The acoustic model employed simulates the noise radiation from a turbojet aircraft engine, in flight, at low to medium specific thrust levels such as landing or steady cruise flight. It therefore includes the diffraction of sound at both duct ends and the mean convection of sound by the axial duct and external flow fields. However, the refraction effects due to nonuniform exterior flow fields which are encountered near the inlet and exhaust under conditions of high thrust (i.e., takeoff) are excluded. This study is presented in two parts. The first part deals with the theoretical development of the model utilizing the Wiener–Hopf techniques. The second part presents some computed radiation characteristics for typical duct configurations.

ISSN:0001-4966    

DOI:10.1121/1.385176

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Computed numerical results are presented for the sound radiation from a finite length unflanged hard wall circular duct with uniform axial flow both inside and outside the duct. The development of the necessary theory is outlined in part I of this report. In the present report, some of the finite duct effects are quantitatively presented for the simplest plane‐wave excitation case, It is shown that the finite duct radiation problem exhibits two important physical phenomena. Firstly, length resonance effects lead to the creation of standing waves on either side of the source plane, in the duct interior. Secondly, the diffracted sound waves propagating from each duct end, interfere in the farfield producing a modified radiation directivity (relative to the semi‐infinite duct radiation).

ISSN:0001-4966    

DOI:10.1121/1.385177

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In a series of recent papers, claims have been made that the human voice carries information that is available to a listener for the identification of certain physical characteristics of the talker. In this note these claims are challenged, both by a reanalysis of some previous data using more‐standard statistical tests, and by an experiment in which equally significant results were obtained by guessing ’’talker’’ weights without listening to speech samples.

ISSN:0001-4966    

DOI:10.1121/1.385178

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Tanner and Rivette [J. Acoust. Soc. Am. 36, 1465–1467 (1964)] reported that three native speakers of Punjabi were unable to discriminate frequency differences an order of magnitude greater than the usual DL’s for frequency. This paper is often cited as evidence for culture‐bound effects in frequency discrimination. We obtained frequency DL estimates from 34 observers comprising a number of linguistic groups, including Punjabi. No evidence of a disability in frequency discrimination was found in any of the groups.

ISSN:0001-4966    

DOI:10.1121/1.385179

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The two points raised in Divenyi’s letter yield a highly unlikely result when jointly considered: That the people of Java may have difficulties understanding speech.

ISSN:0001-4966    

DOI:10.1121/1.385180

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP