摘要:

This paper presents a numerical evaluation of the rigorous solution to the wave equation for the internal field of an underwater, spherical, liquid lens that is being irradiated by plane waves. The numerical computations, which were performed for three refracting liquids with indices of refraction 1.8, 2.25, 2.82, and for the range 1⩽d/λ0⩽15 (d, the diameter of the lens; λ0the wavelength in water), are presented graphically. The relative pressure and the relative intensity were computed along the axis of the lens. It was found that the intensity is not proportional to the square of the pressure and, furthermore, that the focal point for the intensity field did not always coincide with the focal point for the pressure field. Since hydrophones commonly used for measurements in underwater acoustics are pressure‐sensitive, only the focal point for the pressure field was considered. Pressure polar patterns were then calculated at the focal point for the pressure field. Also, the beamwidth and gain were determined as a function ofd/λ0. In general, the theoretical results were found to be in good agreement with the experimental observations of W. J. Toulis [J. Acoust. Soc. Am.35, 286–292 (1963)].

ISSN:0001-4966    

DOI:10.1121/1.1909695

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Measurements of ambient noise under shore fast pack ice during winter revealed two distinct noise‐producing mechanisms. One mechanism was the production of tensile cracks at the surface of the sea ice by thermal stresses caused by decreasing air temperatures. The resulting ice‐cracking sounds produced impulsive noise. The second mechanism was the interaction of the granular ice surface with the wind, which produced Gaussian noise. Separate pressure spectra are presented for underwater noise generated by each mechanism. The spectra and the statistical properties of the underwater noise appeared to be related to the local meteorology and the temperature changes within the ice cover.

ISSN:0001-4966    

DOI:10.1121/1.1909697

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

This paper describes the design and construction of a line transducer with a conical‐shell directivity pattern. The desired beam orientation is obtained through a combination of physical spacing of the elements of the line, connection of elements, and phasing of the driving voltage. Minor‐lobe reduction is achieved through the use of elements cut to size to provide a shaded distribution. Measurements show the minor lobe to be about 20 dB below the main‐lobe level. This particular transducer was designed to obtain bottom and surface backscattering data at 40 kc/sec for a grazing angle of 30° through all azimuthal angles.

ISSN:0001-4966    

DOI:10.1121/1.1909699

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The burning of a combustible‐gas mixture after passage through an electrically controlled flow modulator can increase the acoustic output by 10–20 dB over the no‐combustion condition. The pyroacoustic amplification appears to result from a thermal interaction of the flameholder with the flame, to achieve a high degree of positional stability for the combustion reactions. This forces the gas‐burning rate to fluctuate with the modulation, and results in enhanced acoustic output. A conceptual model of the phenomenon has been developed that agrees with the experimental facts. The largest device of this kind constructed to date produced a sound‐pressure level on the horn axis that would be the same as that from a piston source of 9.1 acoustic watts in an infinite baffle. The electrical power was 5.2 W, the pneumatic power less than 7 W, and the thermochemical input approximately 400 W.

ISSN:0001-4966    

DOI:10.1121/1.1909701

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The methods for computing loudness developed by Zwicker [Acustica2, Akust. Beih.1, 125–133 (1952); Acustica8, Akust. Beih.1, 237–258 (1958)] and Stevens [J. Acoust. Sac. Am.28, 807–832 (1956);11, 1577–1585 (1961)] were applied to several complex sounds encountered in our work on architectural acoustics. The loudnesses computed on the basis of Stevens' method did not agree closely with the loudnesses computed by Zwicker's method, and the results obtained by using the two methods were not related to one another in any consistent way. Further, studies with subjects showed that both sets of computations gave results at variance with the responses of the subjects. Investigation of the loudness‐versus‐frequency contours for our subjects showed closer conformity to the Fletcher and Munson [J. Acoust. Soc. Am.5, 82–108 (1933)] data than to the more recent equal‐loudness contour reported by the National Physical Laboratory [Brit. Std. 3383, Brit. Stds. Inst. (1961)], the functions reported by Zwicker, or the band‐pressure levels that form the basis for the loudness weighting in Stevens' method. However, this feature does not suffice to account for the discrepancies observed.

ISSN:0001-4966    

DOI:10.1121/1.1909703

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

In this paper, we describe a technique using nuclear‐spin saturation that will accurately determine crystal sonic resonances and measure sound velocities at any temperature, and, in particular, when the crystal is immersed in a liquid coolant such as liquid nitrogen. The results of the experiment show that the internal energy density increases by a factor of 10 as one changes the frequency from a crystal nonresonance to a crystal resonance. We derive an expression relating the voltage on a driving transducer bonded on one end of the crystal to the internal energy density of the added phonons and compare this with out experimental results.

ISSN:0001-4966    

DOI:10.1121/1.1909705

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

This paper presents measurements of speed of sound in compressed fluid parahydrogen. The measurements cover temperatures from 15 to 100°K and pressures to 300 atm. Calculations based on previous pressure, density, and temperature measurements of this laboratory provide the density corresponding to each experimental temperature and pressure. These measurements complement previous thermodynamic data on parahydrogen of this laboratory, giving extensive verification of sound‐speed calculations based on those measurements. Prior to this work, no known experimental speeds had been determined for compressed liquid parahydrogen above 21°K.

ISSN:0001-4966    

DOI:10.1121/1.1909707

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The propagation of torsional waves in composite, infinitely long, tractionfree, circular, cylindrical rods is investigated on the basis of the three‐dimensional linear theory of elasticity. The composite rods consist of an internal circular rod made of one material, bounded by and bonded to a circular casing made of another material. The effect of the variation of the geometric and physical parameters on the frequency of the torsional motion is discussed. It is shown that, in general, for composite rods, the first torsional mode (no nodes along the radius) may not exist uncoupled.

ISSN:0001-4966    

DOI:10.1121/1.1909709

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Experimental results are presented that verify the theoretical conclusion that an inverted pendulum may be stabilized with second‐order stationary, random parametric excitation having a discrete‐power spectral density. Experiments also verified that the theoretical condition on frequency spacing is critical.

ISSN:0001-4966    

DOI:10.1121/1.1909711

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The problem of the nonstationary excitation and, hence, the nonstationary response of a linear system is treated by assuming that the excitation is a superposition of random pulses. Under this assumption, the response is another superposition of random pulses. The simplest case in which the excitation is a non‐stationary shot noise—that is, the excitation pulses are the Dirac impulses that arrive according to a non‐homogeneous Poisson probability law—is considered first. The log‐characteristic functional of the response process, which gives complete statistical information about the response, is obtained. Then, consideration is extended to an arbitrary shape for the excitation pulses and to non‐Poisson pulse arrivals. For use in the frequency‐domain analysis of the second‐order statistics, the expressions are given for the generalized spectral density of the excitation or the response process. Finally, an example is included for illustration.

ISSN:0001-4966    

DOI:10.1121/1.1909713

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP