摘要:

An expression is derived from which the natural frequencies of a rectangular orthotropic plate, under any combination of simply supported, elastically supported, or clamped boundary conditions, can be obtained. The Mindlin–Timoshenko theory, which includes the effects of transverse shear and rotary inertia, is used to describe the plate motion. The solution is obtained with a previously developed extension of the Galerkin technique. Comparison of results with the limited results of previous investigations is very good. New results are presented for the fundamental frequencies of rectangular and square plates for boundary conditions on all four edges that vary continuously from simply supported to clamped, and for various combinations of length‐to‐thickness ratios and material constants. Additional results are presented for orthotropic plates simply supported and clamped on all four edges.

ISSN:0001-4966    

DOI:10.1121/1.381280

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The theory predicting the dynamic behavior of fluid‐filled porous media is due to Biot. In the theory he accounts for the relationship between the friction force between the two phases, solid and fluid, and the average relative fluid velocity by means of what he calls a viscodynamic operator. Recognizing that the operator makes the solution of the equations difficult, he presents an asymptotic approximation of the operator and introduces it into the equations for linear momentum, which results in an approximate theory which can be used to study wave propagation in the media. Study of the approximation shows that it is particularly suitable when the velocity of the fluid relative to the solid varies gradually with time. This raises the suspicion that the theory may not predict accurately the behavior of transient waves, especially near the head of the pulse. Accordingly, in this paper another approximate theory is developed, following the lead of Biot, this one appropriate when the relative velocity varies abruptly with time. A problem involving transient responses in a fluid‐filled porous half‐space is solved and the responses predicted by the ’’gradual’’ and ’’abrupt’’ theories are compared. The uneasiness concerning the appropriateness of the Boit theory for transient‐wave‐propagation problems proves to be without foundation.

ISSN:0001-4966    

DOI:10.1121/1.381281

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Under the usual assumptions of small strains with moderately large rotations, the problem of the transverse vibrations of highly prestressed, nonuniform annular plates is reduced to the solution of the differential equation governing the transverse vibration of the corresponding prestressed membrane subject to modific boundary conditions that account for the effects of bending. The methods of matched asymptotic and/or composite expansions are used to determine these modified boundary conditions. The agreement of the results of both methods with known exact solutions for simple geometries demonstrates the efficiency of this technique when compared with other well‐known numerical techniques.Subject Classification: [43]40.24.

ISSN:0001-4966    

DOI:10.1121/1.381282

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Transient solutions are presented for an infinitely long simply supported composite plate subjected to either a uniform or line concentrated dynamic pressure at the upper surface of the plate. A rectangular pulse, triangular pulse, and sinusoidal pulse are considered and dynamic load factors determined for maximum values of deflection, bending stress, and interlaminar shear stress as a function of pulse dwell time. Effect of pulse shape on deflection and stresses is also considered. These numerical results are obtained for graphite/epoxy symmetric angle‐ply laminates.

ISSN:0001-4966    

DOI:10.1121/1.381270

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Estimation of the bearing of a farfield signal source with a small‐diameter circular array of hydrophones is studied in this paper. It is shown that for isotropic farfield noise the Cramér–Rao bound can be simply evaluated via a spatial harmonic representation of the array response. Use of the derived expression for practical bearing estimators employing superdirectivity is justified by showing the equivalence between the maximum‐likelihood estimate and one obtained by the formation of superdirective beams. An expression for the average bias resulting from anisotropy of the ambient‐noise field is also derived using a spatial harmonic representation.

ISSN:0001-4966    

DOI:10.1121/1.381271

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Many theories have been developed in past years which have attempted to model the function of the human cochlea. With the recent availability of the physical measurements of Rhode [J. Acoust. Soc. Am. 49, 1218 (1971)], these theories now appear to be inadequate. In this paper, improved numerical solutions have been found for the two‐dimensional cochlear model proposed by Lesser and Berkley [J. Fluid Mech. 51,497 (1970)], using the Green’s‐function method as first suggested by Cox and Lien [(1973) unpublished]. The Green’s‐function method is used to derive an integral equation which may then be solved numerically. This procedure has proven to be stable, accurate, and faster than several other numerical solution techniques that have been tried. With an appropriate selection of the assumed membrane dissipation, the results are seen to agree within a few decibels of the Mössbauer measurements of Rhode, including the sharp change in slope observed in his amplitude ratio measurements just above the best frequency. This plateau occurs at a level which is 58 dB lower in amplitude than the amplitude at the best frequency.

ISSN:0001-4966    

DOI:10.1121/1.381272

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

To develop an objective statistic for quantifying acoustic‐reflex magnitude, a computer sampled baseline and perstimulatory conductance and susceptance. For each component, the difference between baseline and perstimulatory means was divided by the pooled standard deviation of the samples yielding a statistic similar tod′. Componentd′’s were combined by taking the square root of the sum of the squaredd′s. The resultantd′ was used to represent acoustic‐reflex magnitude in an objective, statistically based format. Stimulus level required to elicit reflexes of specific magnitudes was estimated using the PEST adaptive procedure. Magnitude‐intensity functions were determined for a 1‐kHz tone, 50‐ and 300‐Hz wide noise bands, and white noise. Stimuli at estimated levels were then used as references in loudness balances among all stimulus pairs, yielding four equal‐loudness contours. Equal‐loudness and equal‐reflex contours had similar shapes, suggesting a relationship between loudness and the acoustic reflex. The magnitude‐intensity functions were quite steep, indicating that small intensity changes produced large changes in reflex magnitude. We concluded that the data do not permit rejection of the hypothesis that stimuli eliciting equal reflexes are equally loud. However, the quantification technique has value in that the notion of reflex ’’threshold’’ can be replaced with a mathematically rigorous measure of reflex magnitude. Experiments to refine this technique are in progress.

ISSN:0001-4966    

DOI:10.1121/1.381274

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A small perforation (2 mm2) was placed in the posterosuperior quadrant of the feline tympanic membrane (TM). Sound pressures (amplitudes and phases) required for a 10‐μV round window cochlear microphonic (CM) output were measured at third‐octave intervals from 200 to 4000 Hz (a) in front and behind the TM, (b) in open and closed sound systems, and (c) before and after perforation, as were the corresponding voltages across the transducer. Sound pressure (SP) changes in front of the TM after perforation revealed low‐frequency losses, identical in shape and magnitude for both open and closed sound systems, that vary inversely with frequency at a rate of 12 dB/octave below 1600 Hz. The transducer voltage changes, concomitant with SP’s in front of the TM necessary to produce the criterion CM, paralleled the SP changes only in the open system. However, considerably larger voltage changes were found in the closed system, especially between 630 and 2000 Hz. Furthermore, from the SP’s measured on both sides of the TM, the mean effective sound pressure (SPeff) acting on the TM was calculated. The changes in SPeff, taken in reference to a constant CM output, demonstrate that a small TM perforation produces a 10‐dB frequency‐independent loss in transmission.

ISSN:0001-4966    

DOI:10.1121/1.381275

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Characteristics of cochlear microphonic (CM) of guinea pigs, when compensated for electrical capacitive shunting within the cochlea, parallel corresponding mechanical characteristics. Specifically, good agreement is found for the middle‐ear transfer characteristic, basilar‐membrane phase, and cochlear travel times. CM corrections derived from guinea‐pig experiments have been extrapolated to CM recorded in Mongolian gerbils to obtain estimates of middle‐ear and basilar‐membrane characteristics, a cochlear frequency map, and cochlear travel times for both animals. The estimates indicate that basilar‐membrane tuning curves are almost symmetrical in the apical turn. Model experiments suggest that the apparent sharpening of the low‐frequency leg of these curves is produced by a shunting effect of the helicotrema. Comparisons are also made among results obtained with three different electrode configurations: a single electrode in scala media (SM), a differential pair in scalae media and tympani (SM–ST), and a differential pair in scalae vestibuli and tympani (SV–ST). Results from both guinea pigs and gerbils indicate a slight advantage in the SM–ST configuration.

ISSN:0001-4966    

DOI:10.1121/1.381283

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A review is given of studies dealing with the pitch of signals derived from white Gaussian noise: the pitch of a (monotic) band of noise, the pitch of (dichotic) noise with an interaural phase shift, the monotic and dichotic repetition pitch, and the pitch of two interaurally delayed (uncorrelated) noises. The aim of the paper is to establish the relationship of these pitch phenomena and their connection with the pitch of monaurally presented simple tones (place pitch) and complex tones (periodicity pitch). Therefore, new experiments were performed on the pitch of two noise bands with harmonically related central frequencies, and the pitch of (dichotic) noise with interaural phase shifts at two harmonically related central frequencies, as well as the pitch of band‐reject noise. A uniform explanation appears applicable, in correspondence with the theory of the pitch of complex tones, on the basis of the concept of a ’’central spectrum.’’ A simple schematic model of binaural interaction is used to describe the generation of the central spectrum. Pitch data can be accounted for by this model description. The existence region of pitch of dichotic signals is discussed in connection with other binaural functions, like lateralization, binaural beats, and binaural masked level differences.

ISSN:0001-4966    

DOI:10.1121/1.381276

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP