摘要:

A new equation is derived for large amplitude forced radial oscillations of a bubble in an incident sound field. It includes the effects of acoustic radiation, as in Keller and Kolodner’s equation, and the effects of viscosity and surface tension, as in the modified Rayleigh equation due to Plesset, Noltingk and Neppiras, and Poritsky. The free and forced periodic solutions are computed numerically. For large bubbles, such as underwater explosion bubbles, the free oscillations agree with those obtained by Keller and Kolodner. For small bubbles, such as cavitation bubbles, with small or intermediate forcing amplitudes, the results agree with those calculated by Lauterborn from the modified Rayleigh equation of Plessetetal. For large forcing amplitudes that equation yielded unsatisfactory results whereas the new equation yields quite satisfactory ones.

ISSN:0001-4966    

DOI:10.1121/1.384720

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The effect of sediment rigidity on bottom reflection loss, RL=−20 log10‖R‖, whereRis the plane‐wave reflection coefficient, is studied using a computational model. A single inhomogeneous turbidite layer overlying a homogeneous substrate is treated with an emphasis on low frequencies (10 to 200 Hz) and low grazing angles (0 ° to 45 °). We find that sediment rigidity can be neglected for thick layers (∠500 m) while it can produce significant increases in RL for thin layers (∠36 m). The frequency dependence of RL for thin layers has a low‐frequency regime characterized by large peaks (∠25 dB) recurring at short (∠2 Hz) intervals. At high frequencies there remains a persistent increase in RL (∠4 dB). The most important mechanism for sedimentS‐wave excitation is found to be compressional wave conversion at the sediment–substrate interface.

ISSN:0001-4966    

DOI:10.1121/1.384721

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The effect of sediment shear wave propagation on bottom reflection loss (RL) from a typical deep sea sediment layer is analyzed by means of a ray path decomposition of the acoustic field. The amplitude of each shear (S) and the compressional (P) ray is obtained from the interface reflection and transmission coefficients. These coefficients are analyzed by means of an expansion in the parameter ε which is proportional to the relatively smallS‐wave velocity of marine sediments. Ray paths with amplitudes up to order ε2are identified and used to develop a qualitative ray path model of RL.P‐wave conversion at the sediment–substrate interface is the dominant mechanism for sedimentS‐wave excitation. To order ε2, RL is the result of the interference of three waves in the water whose amplitudes are proportional to ε0, ε1, and ε2. Comparison with RL obtained from a computational model shows that the ray path model correctly predicts the dependence of RL on frequency,S‐wave speed,S‐wave attenuation, andP‐wave attenuation.

ISSN:0001-4966    

DOI:10.1121/1.384722

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The three‐dimensional integral solution for the secondary sound produced by a parametric array is formulated in a manner useful for the consideration of broadband or transient primary signals. It is shown that when the primary pressure field can be modeled as spherically spreading from the origin, the low‐frequency secondary sound can be expressed as the convolution of the ’’input’’ to the parametric array with the ’’impulse response’’ of the parametric array. By modeling the primary directivity functions as Gaussian, the impulse response is reduced to a single integral. The ’’frequency response’’ of the parametric array is derived and shown to be the Fourier transform of the impulse response. For the special case of an observer on the axis of symmetry, an exact analytic result for the frequency response is obtained and is compared with previous theories and with experiment.

ISSN:0001-4966    

DOI:10.1121/1.384723

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

This paper describes a materials system for forming rubber composites with selectable acoustic properties. It is particularly suitable for laboratory use in molding small articles with longitudinal sound speeds and impedances less than (or not much greater than) those of water, and with sound absorption coefficients which may be varied over a wide range. The composites are formed using a common silicone rubber resin (RTV‐602) to which various fillers may be added in controlled amounts. In this study, we measured the sound speed, density, and attenuation coefficient for more than 100 samples containing various concentrations and types of these fillers. These data were then reduced to determine the best‐fit coefficients in a set of descriptive equations. Thereafter these equations could be used to calculate the filler concentrations needed to form composites with specific required properties. To demonstrate the usefulness and predictability of these materials in an application of general interest, these composites are used to construct several broadband anechoic coatings which reduce tank wall reflections by 20–35 dB at frequencies from 400 kHz to greater than 7 MHz. One‐ and two‐layer coatings were designed using equations derived from Brekhovskikh’s treatment of sound propagation in multilayer media. These coatings were then molded as tiles, and their actual performance is compared with that theoretically predicted. When applied to the inside walls of ultrasonic testing tanks, these tiles significantly reduce the tank size needed for various laboratory and biomedical applications.

ISSN:0001-4966    

DOI:10.1121/1.384724

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Based on linear one‐dimensional acoustics, a geometrically perfect elastic waveguide would respond to an oscillatory internal pressure only in the presence of path deflectors (elbows and branches). In practice, a significant elasto‐acoustic interaction results even in straight conduits as a result of manufacturing tolerances. A theoretical model of the linear acoustic loading in straight pipes is developed that considers the acoustic wave distortion due to perimeter, axial, and wall thickness nonuniformities.

ISSN:0001-4966    

DOI:10.1121/1.384725

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

AT‐matrix formalism is presented for a multilayered three‐dimensional scatterer of arbitrary shape immersed in a fluid, to study the scattering of acoustic waves. The layers of the scatterer may be composed of elastic or viscoelastic material. Explicit expressions for theT‐matrix of a two‐ and three‐layered scatterers are presented. Frequency dependent numerical results have been obtained for two‐layered prolate and oblate elastic and viscoelastic spheroidal obstacles where the inner layer is assumed to be a cavity. The differential, backscattering, absorption, and extinction cross sections have been obtained for both thin and thick layers. For purposes of comparison, results for the homogeneous scatterers are also presented. The scattering cross sections for a thick outer layer are found to be considerably different from those for a thin layer.

ISSN:0001-4966    

DOI:10.1121/1.384726

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Numerical results are obtained for a finite circular elastic cylinder with spherical end caps using Waterman’sT‐matrix method. In addition to the important practical applications that this geometry has in underwater acoustics, for the first time this method is applied to elastic scatterers that have a discontinuity in the first derivative of the normal to the surface. This makes the problem numerically difficult and is a good test of the effectiveness of theT‐matrix method. The frequency dependence of the backscattering cross section is presented for a cylinder whose overall length is twice its diameter. Our results are compared with experiments showing excellent agreement.

ISSN:0001-4966    

DOI:10.1121/1.384727

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The action of a plane wave upon a sinusoidal pressure‐release surface covering an impenetrable medium is studied by means of the Rayleigh and Waterman theories. It is demonstrated that solutions computed from the Rayleigh theory are obtained in about half the time necessary for the obtention of Waterman theory solutions having the same precision. Furthermore, it is possible to obtain solutions from the Rayleigh theory, at quite reasonable cost, that are at least as precise as those obtained from the integral equation method by Uretsky in connection with the experiments of La Casce and Tamarkin. This proves, contrary to prevailing opinion, that the Rayleigh theory is fully capable of describing the scattering phenomena produced by a wide class of corrugated surfaces, including those whose roughness is rather large. The minimal width of this class is shown herein to be 0

ISSN:0001-4966    

DOI:10.1121/1.384728

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Unmasking in the forward‐masking procedure was investigated in two experiments. In the first, signal frequency (fs) was held equal to the frequency of the primary masker component (f1) while the frequency of a secondary masker componentf2(wheref2≳f1) was varied. In the second experiment,f1andf2were held constant while signal frequency varied. The results are discussed in terms of the effects potential perceptual cues may have on unmasking in the forward‐masking procedure.

ISSN:0001-4966    

DOI:10.1121/1.384729

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP