摘要:

The U. S. Environmental Protection Agency has proposed the use ofC‐weighted day/night level for the assessment of impulse noise such as the noise resulting from sonic boom, blast noise (artillery, armor, demolition, etc.) and other large‐amplitude impulse sources. One remaining question pertaining to the use ofC‐weighting has been the growth function for human response to impulse noise. This question arises because work by Kryter and by Young using peak values and/or small amplitudes exhibited growth functions of 6−7dB for a doubling of annoyance, while the growth function for human response to common sources (planes, vehicles, etc.) increases by about 10 dB for a doubling of annoyance. Kyter’s and Young’s data are reanalyzed herein by usingC‐weighting and by including only large‐amplitude data. This reanalysis results in a growth function for human response to impulse noise which increases by about 10 dB for a doubling of annoyance. This equality of growth function between commonA‐weighted noise andC‐weighted impulse noise further supports the use ofC‐weighted day/night level for assessment of sonic boom, blast noise, or other large‐amplitude impulse noises having similar spectral content.

ISSN:0001-4966    

DOI:10.1121/1.382128

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The usual sensor for acoustic emission is the piezoelectric transducer. Although this transducer is readily available, reasonably inexpensive, and very sensitive to ultrasonic transients, it has several serious drawbacks as a transducer: It distorts the signals being measured, it exhibits resonances, it has limited bandwidth, it responds differently to surface acoustic waves and bulk waves (because of its large sensitive area), and its calibration is a matter of considerable uncertainty. Essentially, it is a qualitative transducer. Furthermore, it cannot measure local effects within a millimeter of an emission source, where the mechanisms causing the ultrasonic transient are presumably most clearly distinguishable. Optical transducers, on the other hand, have the great advantage of providing accurate, quantitative, highly localized information; they do not disturb the waves being measured and are not limited by frequency response.

ISSN:0001-4966    

DOI:10.1121/1.382129

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The voltage response is derived for radially polarized piezoceramic cylinders when pressure is applied on the cylinder inside surface. Both static and oscillating pressures are considered. A 2.54 cm diameter cylinder of PZT‐4 (Vernitron) material is used as a model in the frequency response which is calculated up to 10 MHz.

ISSN:0001-4966    

DOI:10.1121/1.382130

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

An investigation has been made of the frequency dependence of amplitude and phase information when broadband ultrasonic pulses, in the region 1–30 MHz, are reflected from layered targets. An on line computer performing Fourier analysis of sampled ultrasonic pulses allowed both amplitude and phase information to be studied. Layers of various acoustic impedances, velocities, and attenuation have been investigated, and in particular, layers of magnetite grown on mild steel. In all cases excellent agreement between experiment and theory has been achieved. The possible use of the techniques of deconvolution has also been considered for the measurement of the thickness of layers. The methods developed have found application in the problem of determining the thickness of a corrosion layer on the inside surface of a component where access can only be gained through the outer surface.

ISSN:0001-4966    

DOI:10.1121/1.382131

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The generation of laser‐induced stress waves in liquids by the vaporization process and the thermoelastic effect was studied experimentally. A high‐speed camera and special high‐sensitivity stress transducers with a response time of a few nanoseconds have been used for these investigations. The experimental results obtained for water,n‐heptane, and carbon tetrachloride are discussed. For the first time, the individual contributions of vaporization and the thermoelastic effect on stress generation are separated. In addition, tunable high‐frequency acoustic waves, with frequencies up to 60 MHz, have been generated in water by the impact of a laser pulse exhibiting longitudinal mode beating. Since existing theories on the thermoelastic generation of acoustic waves do not yield satisfactory agreement with our experimental data, a new spherical model is proposed, where the transient heating caused by the laser impact, is represented by the three‐dimensional heat pole. This solution of the equation of heat conduction corresponds to a Gaussian distribution of the excessive temperature in space, and thus to the TEM00mode of the incident laser beam. An analytical solution of the thermoelastic pressure wave is derived for this case of temperature distribution. Its good agreement with the experiment is discussed for various liquids and for two different laser characteristics.

ISSN:0001-4966    

DOI:10.1121/1.382132

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

In a previous paper [J. A. DeSanto, J. Acoust. Soc. Am. 62, 295 (1977)] we showed that the solutions of the Helmholtz and parabolic equations were related by an integral transform. The stationary phase approximation of the transform led to corrections of the parabolic approximation (PA). Based on this analysis, we define in this paper a corrected parabolic approximation (CPA) involving the second range derivative of the parabolic field, numerically compare the results to a normal mode example, and show how the CPA reduces the error of the PA. The error reduction is most marked in the phase.

ISSN:0001-4966    

DOI:10.1121/1.382133

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The nonlinear interaction of a monochromatic ultrasonic signal with audio‐frequency noise has been measured in water. The scattered signal lies in sidebands corresponding to the sum and difference components of the frequencies involved. The intensity of the scattered signal increases linearly with interaction distance and quadratically with the signal frequency in the range 1–5 MHz, in agreement with the theory of Westervelt.

ISSN:0001-4966    

DOI:10.1121/1.382134

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This study details the first successful uniformly valid expansion for a multidimensional nonlinear wave in a system described by curvilinear coordinates. The problem of interest is the steady‐state wave motion induced within an inviscid compressible fluid by an infinite circular cylinder executing a harmonic planar vibration in itsnth circumferential mode. The solution is achieved by employing a regular perturbation series to obtain an outer expansion for the velocity potential. Then outer expansions for the pressure and the velocity components are derived by the method of renormalization. Finally, uniformly valid expansions for the response are determined by matching the outer solutions with the results of a linearized analysis, which represent the inner solutions. Examples considering the effect of the nondimensional parameters are treated by presenting pressure and velocity profiles, as well as nodal and antinodal lines of radial velocity. The range of validity for farfield approximations is discussed.

ISSN:0001-4966    

DOI:10.1121/1.382135

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The method derived in Part I for investigating the propagation of weakly nonlinear acoustic waves in systems described by curvilinear coordinates is extended herein to a three‐dimesnional situation. Specifically, this is a determination of a uniformly valid first order approximation to the waves radiating from an infinitely long cylinder vibrating harmonically in a mode having circumferential wave numbernand axial wavelengthL. The phenomenon of self‐refraction, in which the rays, as well as the wavefronts, are distorted by the wave motion, is shown to be the explanation for some unexpected types of distortion in the profiles of the pressure and velocity component waves. An important development is the disclosure that the three‐dimensional case of large, but finite,Lcannot be used to deduce the response in the two‐dimensional case of infiniteLstudied in Part I. The explanation of this situation is found to lie in the existence of a dispersion relation for the phase velocity of linear waves in the three‐dimensional case.

ISSN:0001-4966    

DOI:10.1121/1.382136

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Certain nonlinear acoustic phenomena may be explained in terms of virtual or secondary sources. The parametric array is one classic example [P. J. Westervelt, J. Acoust. Soc. Am. 35, 535–537 (1963)]. It is argued here that there must also exist formally similar sources due to the thermoviscous heating of a fluid by a modulated sound wave. At moderate to high modulation frequencies the nonlinear mechanism dominates, but at sufficiently low modulation frequencies, the thermal phenomenon must become the more significant effect.

ISSN:0001-4966    

DOI:10.1121/1.382137

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP