摘要:

Measurements of ultrasonic attenuation were made in a series of molten chlorides. The data indicate the existence of a structural volume viscosity whose activation energy differed from that for shear flow by from 1 to 6 kcal/mol. The ratio of volume to shear viscosity is the highest found so far (for an isothermal process) in any liquid, lying in the range 17 to 27. It appears that this ratio rises with the strength of intermolecular bonding in the liquid. The logarithm of this ratio of volume to shear viscosity was found to be linearly related to the entropy of fusion. Application of the Eyring‐Hirai “hole” theory of structural relaxation yielded reasonably good agreement with the measured values.

ISSN:0001-4966    

DOI:10.1121/1.1918176

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The power flow between two independently and randomly excited harmonic oscillators is calculated assuming small linear coupling. It is found that for conservative coupling the power flow is proportional to the temperature (average modal energy) difference of the two oscillators. The constant of proportionality is symmetric in the parameters of the two modes and is positive definite although its magnitude depends on the relative sign of the inertial and stiffness coupling. An equivalent circuit for the energy flow between the modes is developed. Finally, we apply the formalism to obtain the motion transmitted through a two‐stage vibration isolator. The method is then extended to the problem where two multimodal systems interact. A particular application is the power flow between several structural modes and a reverberant acoustic field. The reverberant sound field is considered as a temperature bath in which the structural modes are immersed. Using this model the steady‐state partition of energy between the two systems and the parameters which govern this partition are computed. Analog circuits for this problem are also constructed. The radiation resistance for some of the normal modes of a beam are calculated and results of the formalism are illustrated experimentally.

ISSN:0001-4966    

DOI:10.1121/1.1918177

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The response to sound and consequent sound radiation (“radiation scattering”) for one linear resonant mode of a part of a larger structure are analyzed for a general structure. A modal reciprocity relation is established between modal radiation resistance and the transfer function which relates incident sound pressure to modal (“generalized”) force in the absence of motion. Response and resonant scattering are also analyzed for excitation by noise. When all angles of incidence are equally probable, the means‐quare response velocity is inversely proportional to modal stiffness and proportional to the fraction of total damping attributable to radiation; it is independent of all other characteristics of the structure.

ISSN:0001-4966    

DOI:10.1121/1.1918178

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Measurements have been made to relate the acoustic fluctuations, resulting when a series of uniform sound pulses is transmitted through a medium in which there are random variations in space and time of the index of refraction, to the range from source to receiver, the acoustic frequency, and the parameters of the scattering medium. This paper considers the range dependence of the coefficient of variation (which is a measure of the acoustic fluctuations). A tank of water is heated from below causing the warmer, less dense, layers of water to rise by convection. This produces a medium of almost homogeneous turbulence with time and space variations in the temperature microstructure. Experimental results are in good agreement with a theory developed by Mintzer [J. Acoust. Soc. Am. 25, 922 (1953)] which predicts that the coefficient of variation of the acoustic pulses varies as the square root of range from source to receiver. There is some evidence that this dependence may be correct under broader conditions than are required by the theory.

ISSN:0001-4966    

DOI:10.1121/1.1918179

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The theory of transmission of a plane dilatational wave through an infinite plane layer is considered where the three media involved are assumed to be linearly viscoelastic, their properties being specified by four elastic constants. Relations for the complex transmission and reflection factors are obtained as well as for the intensity relations and specific acoustic impedance in the incident medium. The equations of state for a viscoelastic fluid and viscoelastic solid are used to relate the basic elastic constants to the basic propagation constants for the media. The transmission relations are then given in terms of these propagation constants. Computed transmission characteristics for water through steel into air and for water through rubber into air are presented and the dependence of these characteristics on the dissipative properties of the media are shown. These numerical examples illustrate the transition of transmission properties in going from low‐frequency, thin plate conditions to high frequency, thick plate conditions. Special relations for these limiting conditions are also given.

ISSN:0001-4966    

DOI:10.1121/1.1918180

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

A van Atta reflector consists of an array of radiators which are interconnected by transmission paths in such a way that the energy of an incident wave is reradiated back into the direction of arrival. Model experiments on backscattering from acoustic van Atta reflectors are reported. Airborne sound waves in the frequency range between 2.5 and 9.0 kc were used in these measurements. The acoustic van Atta array consists of 36 conical horns (aperture112 in.) arranged on a 9×9‐sq‐in. flat surface. The horns are inter‐connected by plastic tubing with reinforced walls. In these measurements the van Atta reflector shows a uniform backscattering over a wider range of angular orientation than the conventional corner reflector in the frequency range between 2.5 and 6.0 kc. For higher frequencies the angular coverage of the van Atta reflector under test is limited by the directivity of the horns. Some tests on an assembly of two van Atta reflectors, mounted at an angle of 60° with respect to each other, are reported. They show a more uniform angular response as compared to a cluster of corner reflectors in the frequency range from 2.5 to 5.0 kc.

ISSN:0001-4966    

DOI:10.1121/1.1918181

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Tests were run on small cantilever beams in a standing‐wave tube and on a mechanical shaker. Measurements were made of tip amplitude and root strain at resonance for a given sound pressure level and input acceleration. Comparison of these measurements indicates that the acoustic pressure required to produce the same root strain (or tip amplitude) that would be caused by a given input acceleration varies inversely as the cube of the specimen's natural frequency.

ISSN:0001-4966    

DOI:10.1121/1.1918182

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The radiation impedance on an unbaffled, rigid circular piston whose back side is surrounded by a small enclosure is deduced from published values of the impedance on oscillating oblate spheroids.

ISSN:0001-4966    

DOI:10.1121/1.1918185

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1918186

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The discovery of the fact that the frequencies of the upper partials of a fixed free beam will be modulated by an existing vibration in the fundamental mode is recounted. It was found, for example, that the frequency of the second partial varied bicyclically in an amount determined by the amplitude of the fundamental mode of vibration.

ISSN:0001-4966    

DOI:10.1121/1.1918187

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP