摘要:

The actual phase modulation introduced in a light beam by reflection off a surface corrugated in an arbitrary manner is calculated. The forms of the light intensity distribution in the reflection of a uniform‐ or Gaussian‐intensity monochromatic circular light beam from a sinusoidal cylindrically corrugated surface are given.

ISSN:0001-4966    

DOI:10.1121/1.1912825

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Acoustic phase velocity surfaces and ray directions in paratellurite,TeO2, have been calculated. Characteristic features of the wave propagation in this highly anisotropic medium have been optically confirmed using the shadow method and Schaefer‐Bergmann diffraction technique. A small misalignment of the wave normal direction has been found to degrade seriously the performance characteristics of acoustic or acousto‐optical devices composed of a highly anisotropic medium such asTeO2. The existence of the transverse mode with a zero temperature coefficient of velocity has been also confirmed by the present calculation and experiment.

ISSN:0001-4966    

DOI:10.1121/1.1912826

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A study of the effect of microphone design on sound absorption and velocity measurements has been carried out for pressures ranging from 1 to 18 atm. Results of this research show clearly that losses may be introduced by the microphone itself and that this problem becomes more severe with increasing pressure. A microphone has been developed which completely eliminates such effects at lower pressures and greatly reduces them at higher pressures. Measurements inCH4gave a pressure dependence of the effective specific‐heat ratio in good agreement with theory. Extrapolation to zero pressure gave a result in good agreement with that obtained by using the vibrational specific heat calculated from the Planck‐Einstein formula. Relaxation times τvwere determined as a function of pressurep0and lead to the averaged valuep0τv = 1.565±0.013 (μsec⋅atm). This is in good agreement with recent results using the spectrophone method (1.60 μsec⋅atm) and in significant disagreement with results obtained from fluorescence experiments (1.90 μsec⋅atm). Data obtained forO2gave relaxation timesτv = 3.34(−2) sec⋅atmat room temperature andτv = 2.36(−2) sec⋅atmat a temperature of approximately 50°C. The room‐temperature value is higher than previously published data by a factor of 2 and is in reasonably good agreement with extrapolation of high‐temperature shock‐tube data. The value obtained at 50°C is in still better agreement with this extrapolation.

ISSN:0001-4966    

DOI:10.1121/1.1912827

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The effect of particle viscosity, when it is at least one order of magnitude greater than that of the suspending medium, has been included in the formula, existing in the literature, for the velocity of sound in suspensions or emulsions. The corresponding coefficient of viscous absorption and cross section for scattering of sound energy have also been calculated. The hydrodynamic dispersion of the velocity of sound, due to the frequency‐dependent nature of the viscous interaction between the particles and the suspending medium, has been shown to exist in suspensions or emulsions.

ISSN:0001-4966    

DOI:10.1121/1.1912828

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Scattering of a plane wave, obliquely incident on an infinite‐elastic conducting solid cylinder, which is freely suspended in a viscous conducting fluid, is considered. The wave motion in both fluid and solid is analyzed into viscous (shear), thermal, and dilatational components. Thus the dissipation, associated with the generation of highly damped viscous and thermal fluid waves at the boundary of the cylinder, is calculated. For a given frequency, this is shown to be a function of the cylindrical harmonic amplitudes of the scattered dilatational wave and of the angle of incidence. Results are presented for the simplified situation of normal incidence and small cylinder radius.

ISSN:0001-4966    

DOI:10.1121/1.1912829

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Transmission of random noise through dense corn, a dense hemlock plantation, an open pine stand, dense hardwood brush, and over cultivated soil was measured. The relation between attenuation and frequency in these diverse cases suggested models that permit the prediction of attenuation in any configuration of vegetation and soil. The corn crop had an excess attenuation of 6 dB/100 ft for each doubling of frequency between 500 and 4000 Hz. On the other hand, the stems of the hemlock, pine, and brush all reduced noise by only about 5 dB/100 ft at 4000 Hz. Bare ground attenuates frequencies of 200–1000 Hz, and the frequency of maximum attenuation depends on the soil permeability to air. Thus, tilling the soil reduced the frequency of peak attenuation from 700 to 350 Hz and increased maximum attenuation at 52 m from the source by nearly 80%. Furthermore, earlier conflicting reports of noise attenuation by vegetation appear reconciled if ground attenuation is taken into account. Scattering and ground attenuation are the principal factors in sound attenuation by vegetation. Both factors attenuate relatively less sound as distance from the sound source increases. Hence measurements far from the source can underestimate the effect of a narrow band of vegetation or soil.

ISSN:0001-4966    

DOI:10.1121/1.1912830

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Angular deflection and the formation of a line caustic are examined for acoustic rays passing through a cylindrical vortex with a viscous core. Ray paths are displayed in normalized form and appear to be applicable to the aircraft‐wake problem as well as to long‐distance sound propagation through synoptic weather features.

ISSN:0001-4966    

DOI:10.1121/1.1912831

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

A review is given of the pertinent equations necessary to describe the reflected and refracted waves at a plane boundary between anisotropic media and the utility of the wave surface in discussing this problem. The critical angle phenomenon in anisotropic media is discussed in terms of the energy flux vector associated with the reflected and refracted modes. The critical angle is shown to occur generally at that angle of incidence for which the energy flux vector of the reflected or refracted mode is parallel to the boundary and not when the wave vector is parallel to the boundary. The possibility of not needing a nonhomogeneous surface wave to satisfy the boundary conditions at angles of incidence greater than the critical angle is discussed for certain particular regions in some anisotropic materials.

ISSN:0001-4966    

DOI:10.1121/1.1912832

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The refraction of acoustical waves by a moving medium layer is theoretically treated and the reflection and transmission coefficients are determined. The moving‐medium‐layer velocity is uniform but with a space dependence in one direction. A partitioning of the moving medium layer into constant‐velocity sublayers is introduced and numerical results for a three‐sublayer approximation of Poiseuille flow are presented. The degenerate case of a single constant‐velocity layer is also treated theoretically and numerically. The numerical results show the reflection and transmission coefficients as functions of the peak moving‐medium‐layer normalized velocity for several angles of incidence.

ISSN:0001-4966    

DOI:10.1121/1.1912833

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

This paper presents a theoretical study of the vibration and stability of a uniformly curved tube containing flowing fluid. The assumption of the inextensibility of the tube is applied to derive the equation of motion. A solution for the natural frequency is obtained and numerical results are presented. The effects of flow velocity, fluid pressure, and the Coriolis force on the natural frequency are discussed. It is shown that when the flow velocity and fluid pressure exceed a certain value, the tube becomes subject to buckling‐type instability. Critical loads in terms of the flow velocity and fluid pressure are presented for fixed‐fixed, hinged‐hinged, and fixed‐hinged end conditions.

ISSN:0001-4966    

DOI:10.1121/1.1912834

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP