摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.4734348

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet athttp://www.uspto.gov.

ISSN:0001-4966    

DOI:10.1121/1.420410

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Evidence of waves has been observed in Hubble Space Telescope (HST) images of the Comet Shoemaker–Levy 9 impact sites [H. B. Hammel et al., “HST imaging of atmospheric phenomena created by the impact of Comet Shoemaker–Levy 9,” Science267, 1288–1296 (1995)]. The radius of a ring that appears near the fragment G impact site is consistent with an acoustic wave and increases with time. This feature cannot be explained in terms of a naive plane-wave model because it appears to expand at a rate that is slower than the speed associated with its radius. This behavior can be explained in terms of multipath propagation in the sound channel. According to this hypothesis, acoustic waves corresponding to different group speeds followed paths that passed in and out of the relatively thin debris layer in which the feature appears. Matched-field processing for the depth of the source indicates that the fragment G explosion must have occurred deep in the water clouds if the ring indeed corresponds to an acoustic wave.

ISSN:0001-4966    

DOI:10.1121/1.420303

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A new lossless poroelastic wave propagation theory is verified by means of ultrasonic transmission measurements on artificial rock samples in a water-filled tank. The experiments involved are similar to those performed by Plona [Appl. Phys. Lett.36, 259–261 (1980)]. In this physically and mathematically mutual consistent new theory the coupling terms between the fluid and solid phase of the porous medium are completely determined by the measured wave speeds and the mass densities and constitutive parameters of both constituting phases. Verification of the amplitudes of the received bulk waves in both the time domain and frequency domain provide information on the validity of the combined effect of propagation characteristics and new macroscopic fluid/fluid-saturated-rock boundary conditions resulting from this theory. The comparison technique between theory and experiments is based on the Fraunhofer diffraction theory, and is first tested in a perfectly elastic medium transmission configuration. Subsequently, this comparison technique is used for the poroelastic medium. It is shown that this technique is very accurate and reliable. The experimental results for the compressional wave and the shear wave in the perfectly elastic medium are in excellent agreement with the theoretical predictions. For the fluid-saturated porous samples, good agreement is found only for the fast compressional wave. For both the shear wave and the slow compressional, it is obvious that there is some kind of loss mechanism involved, which cannot be explained by the current theory. Despite the fact that the bulk losses in the porous medium can be explained qualitatively by the full frequency range Biot theory, it is conjectured that even a quantitative fit is feasible if Johnson’s loss model [D. L. Johnson et al., J. Fluid Mech.176, 379–402 (1987)] is applied in the lossy counterpart of the current theory [T. W. Geerits, J. Acoust. Soc. Am.100, 2949–2959 (1996)].

ISSN:0001-4966    

DOI:10.1121/1.420304

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In this paper, the acoustic scattering by an obstacle across a wide frequency range of sound waves is investigated on the basis of the Helmholtz integral formulation. To overcome the nonuniqueness difficulties, the methods proposed by Burton [NPL Report NAC 30 (Jan 1973)] and by Burton and Miller [Proc. R. Soc. London, Ser. A323, 201–210 (1971)] are adopted for the Dirichlet and Neumann problems, respectively. The aim of this paper is twofold. The first is to bring together completely regular formulations of the Helmholtz integral equation and its normal derivative. The second is to extend these formulations to treat the higher-frequency problems. The weakly singular integrals are regularized by subtracting out one term and adding it back. Depending on the problem concerned, the additional integral can finally be expressed in an explicit form or results in solving a surface source distribution of the equipotential body. The hypersingular kernels are regularized by the method of using some properties of the associated Laplace equation, originally proposed by Chien et al. [J. Acoust. Soc. Am.88, 918–937 (1990)]. The completely regularized integral equations are amenable to computation by direct use of the standard quadrature methods. To study the acoustic scattering due to higher-frequency waves, Filon’s quadrature method [Proc. R. Soc. Edinburgh49, 38–47 (1928)] is extended to treat the rapidly oscillatory integrands. Numerical examples consist of acoustic scattering from a hard or soft sphere of radiusaacross a wide spectrum of wave numberska=π–20π.Comparisons of the numerical results with the exact solutions demonstrate the validity and efficiency of the implementation.

ISSN:0001-4966    

DOI:10.1121/1.420305

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The nonlinear dynamic equations introduced by Biot to model porous media have not been implemented to describe nonlinear acoustic waves in such media. In this work the equations are revised and a mathematical model depicting the physical nonlinearity is established. A perturbation technique is then applied to find solutions to the nonlinear Biot equations. An important feature of the developed model is the introduction of the dependence of the structural parameters of the medium on its porosity. The model establishes a correlation between the measurable effective nonlinear parameter and structural parameters of the porous medium. This suggests employing nonlinear measurements as a diagnostic tool for porous media.

ISSN:0001-4966    

DOI:10.1121/1.421011

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Rayleigh wave nonlinearity is investigated theoretically. First, spectral forms of the evolution equations for Rayleigh waves and sound waves are used to compare the relative efficiencies of sum and difference frequency generation. Next, time domain forms of the same evolution equations are used to compare the relative importance of local and nonlocal nonlinearity on the distortion of Rayleigh waves in the preshock region. Finally, new analytical approximations are derived for the shock formation distance and the corresponding coefficient of nonlinearity for Rayleigh waves.

ISSN:0001-4966    

DOI:10.1121/1.420306

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A procedure to generate enhanced acoustic streaming into a bounded space has been studied. Under continuous ultrasound radiation, it was difficult to generate enhanced acoustic streaming in bounded space because of disturbances by reflected waves. Efforts were made to remove the disturbances by adjusting the repeat time of tone bursts of ultrasound. An experimental system has been developed for visualizing acoustic streaming. As a consequence of experiments, the streaming velocity in the bounded space has been enhanced by about 2.5 times by using a series of tone bursts of ultrasound.

ISSN:0001-4966    

DOI:10.1121/1.420307

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Detailed measurements of finite-amplitude pulses radiated by plane and focused circular pistons in water are presented. Comparisons of time waveforms and frequency spectra, both on and off axis, are made with numerical calculations based on the nonlinear parabolic wave equation. Emphasis is on nonlinear distortion of amplitude- and frequency-modulated tone bursts. Use of short pulses enabled resolution of the direct and diffracted waves prior to their coalescence and subsequent shock formation along the axis of the source. Because of its relevance to investigations of cavitation inception, attention is devoted to variation of the peak positive(p+)and negative(p−)pressures along the axis of a focused source. It is shown that with increasing source amplitude, the maximum of each shifts away from the focal plane, toward the source. This effect is more pronounced forp−than forp+.

ISSN:0001-4966    

DOI:10.1121/1.420308

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The periodic structure of dispersed particle distributions in a quickly oscillating plane sonic field has been the object of many classical investigations. It is well-known that particles dispersed in a standing one-dimensional sonic wave tend to concentrate either at nodes or at anti-nodes of the fluid velocity. If the amplitude of oscillations is sufficiently small, such that no shock waves can develop, the interaction of a two-dimensional sonic mode with particles in a resonant chamber is analyzed. The chamber considered is bounded by two parallel cylindrical mirrors, which enable the existence of the “bouncing ball” mode concentrated in the neighborhood of the minimal diameter connecting the mirrors centers. If the size of the diameter exceeds the sonic wavelength, the mode magnitude decays rapidly away from the diameter. The domain is filled with fluid, which contains spherical particles. The quantitative theoretical description of the phenomenon of steady forces acting on dispersed particles in the chamber is achieved. The chamber boundary mirrors cause dispersed particles to move in a direction transverse to the diameter, where the “bouncing ball” mode is concentrated. It is shown that in addition to the well-known one-dimensional particle motion along the diameter toward the velocity nodes or anti-nodes, there exists a side drift, which depends on the fluid-to-particle density ratio, the “bouncing ball” mode frequency and the radii of curvature of the resonator’s mirrors.

ISSN:0001-4966    

DOI:10.1121/1.420309

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP