摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.4734349

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.420385

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.420259

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:10.1121/1.420260

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

An active control approach was developed to observe and control nonlinear effects for high-amplitude acoustic waves in a cavity. The acoustic medium was air at ambient pressure and temperature. A harmonic cavity was driven using a multi-frequency drive to selectively drive the fundamental mode and suppress nonlinear interactions between the fundamental and other modes. A semi-empirical model was developed using effective quadratic and cubic nonlinear coupling coefficients to predict resonator response. The cavity was also shown to act as an acoustic mixer. Typical acoustic pressure amplitudes were 1000 Pa (SPL 154 dBre: 20 μPa).

ISSN:0001-4966    

DOI:10.1121/1.420388

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The formation of air-coupled acoustic surface waves over an impedance plane has been studied in a series of model experiments. Surface waves were generated at an impedance discontinuity on a flat surface, one section of the surface being acoustically hard, and the other composed of an array of small cavities with an effective impedance suitable for surface wave propagation. A point source of sound (800 Hz–2 kHz) was located on the hard surface and the vertical sound pressure distribution measured over the impedance plane, at various distances. The formation, propagation, and decay of the surface waves were clearly observed. The measured pressure distributions are consistent with the theoretical formulation of Rasmussen [J. Sound Vib.84, 598–602 (1982)] for propagation of sound over an impedance jump. An alternative formulation for the case of plane waves incident at grazing angles to a surface has been described by McAninch and Myers [AIAA 26th Aerospace Sciences Meeting, paper AIAA-88-0179 (1988)]. This simpler formulation has been found to be consistent with our measurements, and with the Rasmussen theory, when the distance between source and impedance discontinuity is sufficiently large.

ISSN:0001-4966    

DOI:10.1121/1.420389

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The characteristics of tube waves in a borehole, with and without a solid cylindrical mandrel, which may be either elastic or poro-elastic, are compared. With an elastic mandrel, the tube waves are slower, more dispersive, and more sensitive to the formation shear modulus than without. Similarly extensional mode characteristics are compared in the presence of a formation. In the presence of an elastic formation the extensional mode is faster, more dispersive than without, and it is only slightly sensitive to the formation shear properties. These calculated characteristics are in excellent agreement with our measured data. Additionally, the characteristics of tube waves and extensional modes are studied in a borehole in the presence of a concentric liquid-saturated porous mandrel whose acoustic properties are calculated using the Biot theory. The coupling of the tube wave propagating in the annulus with the slow wave propagating in the porous mandrel introduces attenuation and additional dispersion to the tube waves; the effect on the extensional mode is slight. Theoretically calculated and experimentally measured dispersion and attenuation are in excellent agreement with each other, with no adjustable parameters. Whether the mandrel is porous or not, there are two modes which are weakly dispersive in the quasistatic limit. Very roughly, the two modes consist of an extensional mode in the rod and a fluid-based mode in the annulus which are coupled together.

ISSN:0001-4966    

DOI:10.1121/1.420390

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Propagation of antiplane waves in an elastic solid that contains a cracked slab region is investigated. The cracks have a uniform probability density in the slab region, are parallel to the boundaries of the slab, and the solid is uncracked on either side of the slab. When an antiplane wave is obliquely incident on the cracks, it is shown that the average (coherent) motion in the solid is governed by a pair of integral equations. This result is obtained by taking an average of the exact system of equations forNnonintersecting cracks and by lettingNtend to infinity keeping the crack density constant. Then, it is assumed that the average exciting stress near a fixed crack is equal to the average coherent stress, and it is shown that the pair of integral equations yields simple analytical formulas for the complex-valued wave number and the refracted waves inside the slab as well as for the wave amplitudes outside the slab. These quantities depend on incident angle, crack density, frequency, and slab thickness. Numerical results, which are valid for small values of the crack density, are presented as functions of frequency and incident angle.

ISSN:0001-4966    

DOI:10.1121/1.420391

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This paper presents a set of Green’s functions for Neumann and Dirichlet boundary conditions for the Helmholtz equation applied to the interior of a cylindrical cavity which are based on evanescent wave expansions instead of the usual normal mode expansions. The evanescent expansion capitalizes on the known physics of the shell–fluid interaction, given a cavity with flexible walls, providing a pressure field which decays exponentially (in the limit of small wavelength) into the interior of the cavity when the wall vibration is subsonic. Due to this decay the evanescent Green’s functions converge much faster than the conventional Green’s functions which are built up out of the interior eigenmodes of a rigid (or pressure release) cavity. Furthermore, these evanescent Green’s functions can be inverted in a fairly straightforward way to provide the foundations for solving the inverse holography problem, that is, the reconstruction of the normal surface velocity from a measurement of the pressure in the interior.

ISSN:0001-4966    

DOI:10.1121/1.419574

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Acoustic bullets are defined to be waves which maintain their peak amplitude and/or general shape as they propagate in free space. A general theoretical approach is presented to investigate the space-time properties of a new class of acoustic bullets which are defined here as acoustic transient Bessel beams. The approach encompasses both baseband and modulated carrier signal wave fields. Closed form space-time expressions are developed using Fourier and Hilbert transform methods for several special cases of transient Bessel beams. The space-time source distributions for generating such wave fields from planar apertures are developed from the free space wave fields via the use of the Rayleigh surface integral solution for time-dependent fields. Finally, numerical results are presented to illustrate the general space-time characteristics of the acoustic transient Bessel beams.

ISSN:0001-4966    

DOI:10.1121/1.420392

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP