摘要:

The present writer has discussed various aspects of propagation in sediment channels [J. Acoust.Soc. Am.70, 820–824 (1981)]. A simplifying assumption was thatcw, the speed of sound in the water, is constant everywhere. In this sequel it is more realistically assumed thatcwdecreases slowly and linearly with height above the water–sediment interface. Consequently an acoustic barrier exists from the interface to, typically, 100–200 m above it. Acoustic energy in a signal traveling along the sediment channel can tunnel upward through the barrier, thereby causing a ‘‘leakage’’ attenuation along the channel. Equations are derived to describe the acoustic field both in and above the barrier, and a long‐known method yields the amplitude attenuation factor caused by leakage. Using numerical examples from the 1981 article, we find that the leakage factor is a negligible 1% of the factor caused by absorption in the sediment. In this case, the approximation of constantcwwas justified, but for a normal mode nearer cutoff the leakage would increase considerably.

ISSN:0001-4966    

DOI:10.1121/1.389563

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The purpose of this paper is to deconvolve the beam pattern effect from the amplitude distribution of sonar echoes from fish to determine the scattering processes at fish. The paper is a continuation of our acoustic methods to measure fish abundance. It demonstrates a direct procedure for determining the fish density (fish/m3), the probability density function (PDF) of scattering processes at fish, and the PDF of echoes. The procedure uses nonoverlapping echoes from a single transducer sonar system. The integral equation for the echo PDF is in Clay and Medwin [AcousticalOceanography(Wiley, New York, 1977), pp. 476–482]. It relates the PDFs of the sonar outputwE(e), transducer beamwT(b), and scattering process at the fishwF(e). I use the transformationsb=exp(−x) ande=e0 exp(−y) to change the integral to the standard form of the convolution integral. The derivation of expressions of the convolution and deconvolution usingztransformations follow directly. We use a ‘‘home‐style’’ microcomputer for computations. Tests of the deconvolution technique on fish echo PDFs for Lake Michigan alewife show the presence of the alewife (10–12 cm length) and an unidentified group of larger fish having two to three times the length of the alewife. Deconvolution of Lake Superior data for 1978 indicate the presence of smelt and an unknown group of larger fish. Deconvolution of 1979 Lake Superior data gives an echo PDF that can be attributed to smelt. In both lakes, fish density estimates are between 10−4and 10−3fish/m3.

ISSN:0001-4966    

DOI:10.1121/1.389564

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The variation of the velocity of elastic waves and of ultrasonic transit times with the direction of propagation under the influence of an externally applied dc electric field was calculated on the basis of known elastic constants and recently determined effective electroelastic moduli for alpha quartz. Results are presented in graphical form for propagation directions in the three planes defined by the conventional Cartesian crystal axes. For each propagation direction the three possible acoustic modes are considered in conjunction with three mutually perpendicular field configurations.

ISSN:0001-4966    

DOI:10.1121/1.389565

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The Young’s modulus and loss tangent have been measured in air for a number of commercially available polyurethanes. A resonance technique was used for measurements over the approximate frequency range 102to 104Hz and the approximate temperature range 40° to −5 °C. Master curves and Williams–Landel–Ferry shift constants were detemined for the materials tested. The automated data acquisition system used is described. The experimental procedure was found to be a reliable method for determining the viscoelastic constants for extensional wave propagation in elastomeric materials.

ISSN:0001-4966    

DOI:10.1121/1.389566

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A simple method is presented for obtaining the stress tensor for small displacements in nonlinearly strained material. The physics of sonic wave propagation in deformed materials and acoustoelastic effects are discussed, and a feasable experiment is suggested for early diagnosis of plastic deformation. The calculational results for surface wave velocity as a function of applied static stress are presented in tabular form convenient for the experiments.

ISSN:0001-4966    

DOI:10.1121/1.389567

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A solution is presented for the three‐dimensional problem of determining the free vibration frequencies and mode shapes for a rectangular parallelepiped which is completely fixed on one face and free on the other five faces. This problem apparently is previously unsolved in the published literature. The Ritz method is used, with displacements assumed in the form of algebraic polynomials. Convergence is studied. Numerical results are given for the first five frequencies of each of the four symmetry classes of vibration, for five thick parallelepiped configurations, including the cube. Contour plots are exhibited for the modal displacements of the cube. The effects of varying Poisson’s ratio are also observed.

ISSN:0001-4966    

DOI:10.1121/1.389568

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The one‐dimensional scalar differential equation describing the extensional motion of thin piezoelectric rods is obtained from the general nonlinear three‐dimensional description. Only the elastic nonlinearities are considered. The relations between the quadratic and cubic coefficients of the rod and the fundamental anisotropic elastic constants of various orders are derived. The quadratic rod coefficients are calculated for various orientations of quartz rods, but not the cubic rod coefficients because the fundamental elastic constants of fourth order, which are required for the calculation, are not presently known. The nonlinear equation and boundary conditions are applied in the analyses of both intermodulation and nonlinear resonance of quartz rods. In each instance a lumped parameter representation of the solution, which is valid in the vicinity of a resonance, is obtained and the influence of the external circuitry is included in the treatment.

ISSN:0001-4966    

DOI:10.1121/1.389569

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

An analysis is presented for the free vibration of circular‐segment‐shaped membranes and plates of rectangular orthotropy. A circular‐segment‐shaped membrane is formed on an orthotropic rectangular membrane by fixing several segments. With the reaction forces acting on the edges of an actual membrane regarded as unknown harmonic loads, the stationary response of the membrane to these loads is expressed by the use of the Green’s function. The force distribution along the edges is expanded into Fourier series with unknown coefficients, and the homogeneous equations for the coefficients are derived by restraint conditions on the edges. For a circular‐segment‐shaped plate clamped at the edges, it is formed on a rectangular plate simply supported at the edges, in which the bending moments act on the edges in addition to the reaction forces. In this case, the moments regarded as unknown harmonic loads are also expanded into Fourier series with unknown coefficients, and are included in the equations for the coefficients. The natural frequencies and the mode shapes of the actual membrane or plate are determined by calculating the eigenvalues and the eigenvectors of the equations. The method is applied to circular‐segment‐shaped membranes and plates of rectangular orthotropy, the natural frequencies and the mode shapes of the membranes and plates are calculated numerically, and the effect of the shape and orthotropy is discussed.

ISSN:0001-4966    

DOI:10.1121/1.389570

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

This paper is the third in a series dealing with the development of temporal sampling strategies for estimation of mean noise levels in the vicinity of airports. It extends the previous analysis for westcoast, one‐direction airports (due to prevailing winds) to eastcoast, multidirection airports (Boston Logan, Washington Dulles, and National). The results show that the data for many of the eastcoast airport sites are nonstationary in the mean level and the corresponding consecutive sampling requirements predicted by the Dynamic Data System (DDS) methodology are very large, at times exceeding 1/3 of a year. When the data are stationary, Monte Carlo simulations using the data produce sampling requirements comparable to the values obtained by the DDS methodology. However, the DDS methodology tends to overestimate sampling requirements for nonstationary data. The simulations demonstrate that nonconsecutive sampling strategies reduce the overall sampling requirements for nonstationary data. In general, the results reveal the following: (a) Westcoast (one‐direction); ±50% precision—four weeks, any sampling strategy, ±35% precision—eight weeks, any sampling strategy. (b) Eastcoast (multidirection); ±60% precision—four weeks, one from each quarter, ±40% precision—eight weeks, one from each eighth.

ISSN:0001-4966    

DOI:10.1121/1.389571

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

As the inadequacy of reverberation time as a predictor of the acoustical quality of auditoria has been recognized, many new measures have been proposed. Of these, early‐to‐late sound ratios and interaural cross correlations are generally accepted as correlates of two major aspects of acoustical quality. Accordingly, the present work includes a large number of measurements of these quantities in halls ranging from 200 to 2500 seats. The purpose of the work was to improve familiarity with the newer measures, to provide more published data, and to explore the dependence of these measures on other quantities. Variations of the new measures were examined within and among halls. Halls that are apparently similar in terms of reverberation times showed clearly identifiable differences when early‐to‐late sound ratios were considered.

ISSN:0001-4966    

DOI:10.1121/1.389572

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP