ISSN:0001-4966    

DOI:10.1121/1.416194

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.416306

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.416972

出版商:Acoustical Society of America    

年代:1996

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:10.1121/1.415966

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Concerns about noise in the community date back to the dawn of recorded history. Then, after centuries of relatively little activity, scientific interest grew during the 17th century and social concerns were again voiced during the 19th century. Many of the wave‐propagation mechanisms relevant outdoors were understood at least qualitatively by the late 1800s. Today, knowledge of sound propagation phenomena is of great economic and social importance because of environmental and other concerns. Reality is more complicated than geometrical spreading above flat ground. Some grounds are acoustically hard like concrete, and others soft as snow. Corresponding reflection coefficients are complex and vary with angle. Grounds may not be flat, leading to shadow zones or alternatively multiple reflections at the ground. Gradients of wind or temperature refract waves either upwards (upwind or in a temperature lapse) or downwards (downwind or in a temperature inversion). Atmospheric turbulence causes fluctuations in the acoustical effects. Many of these features mutually interact. Measured sound pressure levels owe as much to near‐surface weather and to ground shape and impedance as to acoustical factors such as source and receiver heights and their separation. This tutorial paper emphasizes field measurements and simple physical interpretations.

ISSN:0001-4966    

DOI:10.1121/1.415879

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Vector sound intensity (i.e., sound‐power flow per unit area) can be used to locate sound sources. In a previous paper [J. Acoust. Soc. Am.97, 856–866 (1995)] it was shown experimentally that the direction of a source can be determined with a vector sound‐intensity probe within ±2°. It was also shown that the directions of two continuous, noncoherent sources can be found with a single sound‐intensity probe, using the spectral characteristics of the sources and/or spectral subtraction. In the present theoretical paper, it is demonstrated that a system of two vector probes can determine both the spatial coordinates and the sound‐power output of two monopole sources through numerical solution of a set of nonlinear equations by the method ofpolynomialcontinuation. This procedure can be extended to a greater number of sources and an equal number of probes.

ISSN:0001-4966    

DOI:10.1121/1.416198

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Mathematical expressions are derived for the far‐field backscattering amplitude spectrum resulting from oblique insonification of an infinite, transversely isotropic elastic cylinder by a plane acoustic wave. The normal‐mode solution is based on decoupling of the scalar potential representing the horizontally polarized shear wave from those of the compressional and vertically polarized waves. The solution degenerates to the well‐known simple model for isotropic cylinders in the case of very weak anisotropy. The solution is used to study the influence of each element of the stiffness matrix on the various resonant modes of vibration. Perturbations of the elementsc33andc44, which characterize the cylinder along the axis, significantly affect resonant frequencies corresponding to axially guided waves. Perturbations ofc11andc12, which characterize the material on the transverse plane, predominantly affect the Rayleigh and Whispering Gallery resonance frequencies. Perturbations ofc13affect all three types of resonances. These results are consistent with elasticity theory and the known modal shapes of these resonances.

ISSN:0001-4966    

DOI:10.1121/1.415868

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Recent studies of plane wave scattering by finite, evacuated cylindrical shells at oblique incidence describe monostatic echo contributions from surface elastic waves. These waves follow helical paths along the shell’s surface and are guided back in the source direction after reflection from the cylinder truncation. The present research examines similar effects viewed in the time signature of a high‐resolution acoustic imaging system. The experimental technique utilizes a narrow beam consisting of a short tone burst to probe a cylindrical shell along its axis of symmetry. The echo returns contain information which yields insight into local scattering processes at the impedance discontinuities of the finite scatterer. The cylindrical shell has a thickness‐to‐radius ratioh/a=5.5%. It is immersed in water and is subject to both exterior and interior fluid loading. Prominent artifacts are shown to coincide with near axial coincidence of thes0anda0Lamb waves. The echo contributions are extremely sensitive to the angle of incidence and interior fluid loading. By placing small ‘‘cuts’’ along the cylinder, it is possible to mimic the truncation effects for different scattering processes.

ISSN:0001-4966    

DOI:10.1121/1.415888

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A three‐dimensional finite‐difference (FD) method is used to simulate sonic wave propagation in a borehole with an inhomogeneous solid formation. The second‐order FD scheme solves the first‐order elastic wave equations with central differencing in both space and time via staggered grids. Liao’s boundary condition is used to reduce artificial reflections from the finite computational domain. In the staggered grids, sources have to be implemented at the discrete center in order to maintain the appropriate symmetry in an axisymmetric borehole environment. The FD scheme is validated for multipole sources in three special media: (i) a homogeneous medium; (ii) a homogeneous formation with a fluid‐filled borehole; and (iii) a horizontally layered formation. The staircase approximation of a circular borehole introduces little error in dipole wave fields, although it causes a noticeable phase velocity error in the monopole Stoneley wave. This error has been drastically reduced by using a material averaging scheme and finer grids. Numerical examples show that the FD scheme can accurately model 3‐D elastic wave propagation in complex borehole environments.

ISSN:0001-4966    

DOI:10.1121/1.415869

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

In this paper a new nondestructive ultrasonic technique is developed to distinguish small spherical voids from small spherical elastic and rigid inclusions. In many materials, such as light metal casting alloys, ultrasonic scattered echoes from void‐type defects and heavy metal inclusions used for strengthening purposes can give the ultrasonic signal of the same order of magnitude. It is shown in this paper how one can extract the phase information of the reflected signal to distinguish the voids from solid inclusions. When phase–frequency curves are extended to the zero frequency, then voids and solid inclusions meet at two distinct points on the phase axis separated by a distance of approximately 180°. Thus voids and solid inclusions can be clearly distinguished. Experimental results are verified by theoretical predictions.

ISSN:0001-4966    

DOI:10.1121/1.415965

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP