摘要:

Starting from the Navier‐Stokes equations, general equation governing the generation of vorticityRis obtained:∇2R = μ0−1∇ × ∇ ⋅ 〈ρ0uu〉, whereinRis the time‐independent vorticity in the Eulerian frame and 〈ρ0uu〉 is the average value of Reynolds' stress dyadic. The solution to this vorticity equation, when properly transformed to the particle coordinates, is shown to be divergence free.A specialization of the vorticity equation to the case of solenoidal first‐order motion is shown to lead to the generating term employed by Rayleigh and by Schlichting; a specialization to the case of irrotational first‐order motion is shown to lead to the generating term employed by Eckart. The sum of the two specialized driving terms does not equal the general term, indicating that the contributions to vorticity from rotational and compression effects are not independent of one another.The theory is applied to find the streaming generated by a well‐defined beam of sound giving results agreeing with Eckart and with Markham. However, when it is applied to a two‐dimensional standing wave problem, the configuration of the streaming velocity in the boundary layer is found to differ from the results obtained by Rayleigh.Finally, the effect on streaming of a time‐dependent viscosity coefficient is examined.

ISSN:0001-4966    

DOI:10.1121/1.1907009

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Theories for calculating steady streaming associated with sound fields are reviewed, comparing the methods and approximations of various authors. Two illustrative problems are worked out, both for rectilinear flow due to irrotational sound fields. The first deals with a single attenuated plane wave traveling down a tube, as in Cady's quartz wind experiments. In the second, a pair of crossed plane waves is treated, giving rise to a quite different kind of streaming. In obtaining solutions, attention is given to boundary conditions; here, gradients of She excess static pressure, another second‐order quantity, come into consideration. Significantly, streaming speeds depend critically upon α, the attenuation constant, where α may be due to any common cause, such as heat conduction, scattering, thermal relaxation, etc. From these results it appears that streaming measurements cannot be used to distinguish between absorption mechanisms. Numerical values are given for a few cases; high flow speeds may be expected in a bubbly medium.

ISSN:0001-4966    

DOI:10.1121/1.1907010

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The effect of a finite circular baffle board on the acoustic radiation was computed by the use of the oblate spheriodal wave function developed by Kotani and by Boukamp. The directivity, power radiation, and radiation impedance of the vibrating disk with a concentric circular baffle board are shown together with a design diagram for a circular baffle board.

ISSN:0001-4966    

DOI:10.1121/1.1907012

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A method for the precise measurement of the velocity of sound is described in which the driving‐point impedance of a loudspeaker connected to a closed tube of variable length is the frequency‐controlling element of a bridge‐stabilized oscillator. The operation of the system and the accuracy of measurement are analyzed. Results of measurements in air at 1 kc/sec, room temperature, and atmospheric pressure yield, when corrected to standard conditions, a velocity of 331.45±0.05 m/sec.

ISSN:0001-4966    

DOI:10.1121/1.1907013

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

As an aid to acoustical designers, this paper presents some experimentally determined values of the attenuation coefficient and the speed of propagation of sound in Fiberglas. The propagation parameters α and β in the equation for a plane wavep = p0εjωt−(α+jβ)zare determined by comparing the amplitudes and phases of the sound pressures existing simultaneously at separate points in the Fiberglas. The principle of measurement is similar to that used by Beranek and Scott involving a longitudinal movable probe in a long narrow metal duct filled with rockwool. However, in the redesigned apparatus, edge effects were reduced by using a tube of larger cross section; wall vibrations were damped by laminated rubber and Masonite walls; and the shunting effect of the longitudinal probe hole was eliminated by the use of transversely inserted microphones.Experimental data were obtained within one db for frequencies between 50 and 1000 cycles for two samples of Fiberglas with nominal weights of 9 lb/cu ft PF (hard) and414 lb/cu ftTWF (soft). The direction of propagation of the sound was normal to the surface of the blanket. For both samples the attenuation increases almost as the square root of the frequency, but the speed of propagation is found to increase almost as the14and12root of the frequency for the hard and the soft samples, respectively.

ISSN:0001-4966    

DOI:10.1121/1.1907014

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

It is shown that in reverberation time measurements warble tones give greater accuracy at the lower frequencies, and white noise at the middle and higher frequencies, this behavior being within a wide range independent of room volume.

ISSN:0001-4966    

DOI:10.1121/1.1907015

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

An automatic recording double crystal interferometer is described which measures the speed and attenuation of sound at about 11 Mc/sec in gases at pressures of a fraction of a mm Hg.

ISSN:0001-4966    

DOI:10.1121/1.1907016

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A fixed path interferometer, using variable temperature for the measurement of the absorption in gases in the lowf/pregion is described. Its use is illustrated by measurements on argon, neon, air, nitrogen, and nitrogen‐hydrogen mixtures at 250 kc. The values found for argon and neon were above classical by 40 and 65 percent, respectively. The discrepancies are ascribed to Rayleigh cross modes in the ultrasonic waves excited by the quartz crystal transducer rather than to any departure from classical theory. Cross modes and their influence on ultrasonic measurements are discussed. Data on the performance of two crystals at 250 and 500 kc are given.

ISSN:0001-4966    

DOI:10.1121/1.1907017

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

By an extension of the techniques of Lindsay, the reflection from a semi‐infinite attenuating medium is derived for the case of oblique angles of incidence. The results are applied to the design of a water tank each wall of which is assumed to be covered by a sheet of absorbing material. The optimum physical properties of the absorber required to make the tank anechoic in the mesacycle region are then determined theoretically. Experimental measurements at 3.35 megacycles/sec indicate that the properties of tanrho‐crubber are very close to optimum. With a14‐inchthick sheet backed by aluminum the reflection coefficient is about −30 db at normal incidence and rises to −20 db at an incident angle of 60°. Beyond 60° the rubber is of little value in reducing the reflectivity. The results obtained are in good agreement with those expected from the theoretical treatment when modified for reflections from the back surface and the phase difficulties previously described by the author.

ISSN:0001-4966    

DOI:10.1121/1.1906981

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The consonant environments of vowels were varied by forming nonmeaningful stimulus syllables consisting of 72 combinations of six vowels and 12 consonants. The syllables were spoken by subjects, and the duration, fundamental frequency, and relative power of the vowels were measured. All three factors varied significantly in response to changes of the consonant environment. The variations were systematically related to the attributes of the consonants, the most powerful attribute being the presence or absence of vocal fold vibration, followed by manner of articulation and place of articulation, in that order.

ISSN:0001-4966    

DOI:10.1121/1.1906982

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP