摘要:

A novel technique has been effectively utilized in studying the properties of liquids under conditions that are not ordinarily accessible. This technique involves the use of an acoustic standing‐wave field established in a column of one liquid in order to trap an immiscible droplet of another liquid. In the experiment reported here, a filtered ether droplet suspended in filtered glycerine was superheated and acoustically stressed until the combination produced an explosive liquid‐to‐vapor phase transition. The experiment was performed under atmospheric conditions at which the normal boiling point of ether is 35.6°C. The measured tensile strength varied linearly from 17 bars at 130°C to 0 bars at 146°C. Previous measurements of the tensile strength of liquids have not come within a factor of 2 or 3 of the theoretical predictions based on homogeneous nucleation theory, a theory which describes the vaporization conditions for pure liquids. The results reported here are in good agreement with that theory. This novel agreement is attributed to the ability to obtain pure liquid samples by utilizing small (0.5‐mm‐diam) filtered droplets.

ISSN:0001-4966    

DOI:10.1121/1.1912311

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Spectra of ultrasonic cavitation noise were obtained in liquid helium and liquid nitrogen. A subharmonic response at half the driving frequency was found to be present at all times. In the case of liquid helium, the relative intensity of this subharmonic showed a peak at the λ point. The background noise intensity was also higher in heliumII. A tendency for the half‐order subharmonic to increase with static pressure was also found both for heliumIand nitrogen. A correlation between the onset of the subharmonic audible‐frequency noise and the white‐noise background was also found. The variation of the intensity of the first overtone with increasing driving voltage was found to be different in heliumIIthan in other liquids. It is argued that many of these phenomena arise from the effect on bubble dynamics of the efficient heat transport in heliumII.

ISSN:0001-4966    

DOI:10.1121/1.1912312

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The particle velocity profileV(ρ) across the face of a transmitting transducer is shown to have large effects upon the diffraction loss and phase change in the ultrasonic field of the transducer. Various functionsV(ρ), monotonic decreasing from the center to the rim of a circular transducer, were employed. The pulse‐echo response of the transducer was calculated by numerical integration on an electronic computer. It was found that the functionsV(ρ) chosen caused the diffraction‐loss and phase‐change curves to be smoother than in the piston case and caused the respective peaks and plateaus to shift with distance in the Fresnel region.

ISSN:0001-4966    

DOI:10.1121/1.1912313

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The equations governing the progagation of sound in a nonconstant area duct with a one‐dimensional fluid flow are derived by a linearizing perturbation technique. The governing equations are transformed successively into two decoupled linear ordinary differential equations with a variable coefficient. By the appropriate choice of duct shape, the variable coefficient is made constant. The duct shape chosen is semi‐infinite, diverging from the sonic throat. Solutions are obtained for several choices of the parameter ωL/2as, which relates frequency, duct shape, and speed of sound. The solutions exhibit standing‐wave characteristics and reveal certain aspects of energy transfer between the mean flow and sound. The study bears on noise growth and decay in the input and output ducts of certain fluidic amplifiers.

ISSN:0001-4966    

DOI:10.1121/1.1912314

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

One‐dimensional scattering of acoustic waves by the thermal field produced by a sinusoidal spatial distribution of heat sources in a perfect gas is examined analytically. The scattered field is found to consist of a transmitted acoustic wave, a reflected wave, and an entropy wave. When the thermal‐field wavenumber is near the entropy wavenumber or twice the acoustic wavenumber, resonance‐like phenomenon occurs, resulting in large‐amplitude scattered waves.

ISSN:0001-4966    

DOI:10.1121/1.1912315

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A numerical investigation of the nearfield region of a vibrating piston was conducted. While existing literature is not exactly clear about how close to a transducer a regular beam pattern is formed, the results of this investigation show the limits of operation one can expect. From one interpretation of literature, a −3‐dB beam with a minimum spot size equal to the transducer diameter would be expected to form beyond an axial distancez= 3.89a2/λ. This investigation shows that such a beam forms atz= 0.75a2/λ and has a minimum spot size equal to one‐quarter the transducer radius. These results are verified for transducers witha/λ's ranging from 1 to 20 and can be extended with confidence to highera/λ's. Similar results are also obtained for −1.5‐, −4.5‐, −6.0‐, −7.5‐, −9.0‐, −10.5‐, and −12‐dB beams.

ISSN:0001-4966    

DOI:10.1121/1.1912316

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The dynamic response and stability of a single‐degree‐of‐freedom structural system composed of a hollow or solid sphere connected by a massless supporting member and submerged in a viscous fluid medium is studied. The constitutive relationship between the connecting member and the base is considered to be of a generalized Maxwell model type. Basset's fluid reaction is included in the integro‐differential equation of motion and a closed‐form solution is obtained by means of Laplace transforms. Response curves illustrating the effect of each dimensionless parameter on the response of the system are presented, and a dynamic stability criterion based on the character of the solution is employed to develop a stability profile for the system. It is demonstrated that the dynamic response of the system is significantly influenced by the character of the surrounding fluid medium while the stability or instability of the structure is determined by the relative values of the load parameter and the stiffness‐coefficient ratio.

ISSN:0001-4966    

DOI:10.1121/1.1912317

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Axially symmetric waves in semi‐infinite hollow elastic circular cylinders, with traction‐free lateral surfaces and subjected to a pressure‐step loading, are considered on the basis of the equations of motion derived by McNiven, Shah, and Sackman [J. Acoust. Soc. Amer.40, 784–792; 1073–1076 (1966)]. By using double integral transforms, asymptotic solutions are obtained for the strains as functions of time and material and geometric parameters. Strains are presented for times near the head of the pulse of the extensional mode at the same distance from the finite end for various radii ratiosa* and for different distances but for the same radius ratio. It is of interest to note that, for thin cylinders (a* less than approximately 1.7, owing to its slight dependence on Poisson's ratio), the maximum group velocity of the radial mode is slightly higher than that of the extensional mode although less than the dilatational wave velocity.

ISSN:0001-4966    

DOI:10.1121/1.1912318

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

An approximate one‐dimensional theory is developed for axially symmetric torsional deformation of elastic circular composite cylinders. The cylinders are composed of a core perfectly bonded to an outer casing. The equations of motion accommodate the first two frequency branches of the dispersion relation for symmetric torsional waves propagating along the axis of the cylinder. Important parameters are the ratios of densities, shear moduli, and radii of the core and casing. Dispersion relations obtained from this approximate theory are studied for ranges of values of these parameters, and a comparison made with the results of the “exact” theory, i.e., three‐dimensional elasticity. In order to match closely the results from the exact analysis, two correction factors are introduced, and values are tabulated for typical material and geometric properties. Sufficient conditions at the ends of finite cylinders are obtained to provide a unique solution.

ISSN:0001-4966    

DOI:10.1121/1.1912319

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

In this paper, the propagation of harmonic waves with an arbitrary number of circumferential nodes in an infinitely long two‐layered composite circular elastic rod is investigated. The composite rod is made of a circular solid rod encased by a circular shell having different material properties. The frequency equation derived on the basis of the three‐dimensional linear isotropic elastic theory is presented. The reduction of this equation to the frequency equations for some special problems, such as longitudinal wave propagations, torsional wave propagations, flexural wave propagations, axial‐shear vibrations, and plane‐strain vibrations is discussed. Simplified equations for phase velocities of longitudinal and torsional waves at very long wavelength are obtained. Numerical results, in terms of frequency and real wavenumber, are given for a composite rod made of a soft core with a stiff casing.

ISSN:0001-4966    

DOI:10.1121/1.1912320

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP