• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

SECTION LISTING

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Nov 1982

Volume 72, Issue S1, pp. S1-S108

Return to All Sections
back to top
RSS Feeds
back to top Session P. Physical Acoustics III: Relaxation, Interactions, and Propagation
Contributed Papers
FREE

Self‐de‐excitation of water vapor: Monomer and dimer contributions (A)

Allan J. Zuckerwar

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S26-S26 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Past efforts to interpret experimental data on the de‐excitation rate of the v2(1→0) vibrational mode of water vapor have been thwarted because of the attempt to fit the data to a single relaxation time. In a phenomenological theory proposed here the de‐excitation takes place by means of two parallel reactions: (1) the conventional collisional de‐excitation of the monomer and (2) a two‐step reaction involving association and re‐dissociation of the dimer. The resulting relaxation equation yields two coupled relaxation times. In pure H2O and in mixtures without O2, the reaction rate for dimer association is taken to be very slow, and the relaxation modes are effectively decoupled: the first corresponding to de‐excitation of the monomer and the second to spontaneous dissociation of the dimer. In mixtures of H2O‐air and H2O‐O2, the association rate of the dimer is found to increase strongly, suggesting that O2 serves as an effective “chaperon” for this reaction, and the relaxation modes of the monomer and dimer become strongly coupled. Fourteen sets of past data, representing a wide variety of test conditions and experimental methods, both acoustical and nonacoustical, are organized into three groups−each corresponding to a relaxation mode predicted by the theory.
FREE

Relaxation mechanism for low‐frequency sound absorption by boric acid in sea water (A)

Robert H. Mellen

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S26-S26 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Investigation of the low‐frequency boric acid relaxation in sea water by the resonator method shows that the mechanisms is an exchange reaction with the carbonate system, i.e., B(OH)3 + CO3−2⇄B(OH)4− + HCO3−. However, the absorption is small unless calcium is present; then the system can be modeled as a complex exchange involving the ion pairs CaCO3° and CaB(OH)4+. Theory and supporting experimental results are presented. [Work supported by DARPA.]
FREE

The effect of polymer additives on cavitation inception in water (A)

James E. Brosey and Lawrence A. Crum

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S27 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Measurements are presented of the variation of the acoustic cavitation threshold of water with concentration of the polymer additives polyethylene oxide and guar gum. It was found that small amounts of these additives could significantly increase the cavitation threshold. A theoretical model, based upon nucleation of a gas bubble from a Harvey‐type crevice in a mote or solid particle, is developed that gives good agreement with the measurements. The applicability of this approach to an explanation of cavitation index reduction in flow‐generated or confined jet cavitation, when polymer additives are introduced, is discussed. [Work supported in part by the ONR and the NSF.]
FREE

The effect of pulse length on transient cavitation inception (A)

Ronald A. Roy and Lawrence A. Crum

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S27 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Most ultrasonic systems used for diagnostic purposes employ short acoustic pulse rather than cw operation in order to accomplish imaging or Doppler scanning. It is also commonly thought that these short‐pulse systems, although driven at high acoustic pressure amplitudes, do not induce cavitation effects due to the low duty cycle of the ultrasound. Although stable cavitation typically requires cw operation for its effects to be present, transient cavitation can theoretically occur in pulse lengths as short as one cycle. We have developed a detection scheme utilizing sonoluminescence to observe the cavitation produced by pulses of varying length and repetition rate. Normal detection methods that examine noise emitted by the collapsing cavity can not be used in short‐pulse excitation due to the high spectral content of the pulse itself. We have observed transient cavitation effects (sonoluminescence) in pulse lengths as low as a few tens of cycles and are modifying our apparatus to go to even shorter pulses. [Work supported in part by the ONR and the NSF.]
FREE

Stress waves induced in graphite‐epoxy composite structures by current pulses (A)

Jacques R. Chamuel

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S27 (1982); (1 page) | Cited 1 time

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
A technique to generate ultrasonic waves in graphite‐epoxy composite structures using electrical current pulses flowing in the structure is described. The difference between the thermal expansion coefficients of graphite and epoxy create large stress waves in response to localized heating by current pulses flowing in the individual graphite fibers. Experimental results are presented demonstrating the applicability of the method to nondestructive testing problems. The anisotropic elastic and electrical properties of a T‐300 graphite/DER‐332 epoxy composite plate were determined. In the experiments, a piezoelectric receiver transducer was used to detect the thermoelastic waves in the composite plate. Distinct ultrasonic waves were detected with 20 μsec current pulses below 50 mA.
FREE

Acoustical measurement of energy and momentum accommodation coefficients on polycrystalline platinum (A)

F. Douglas Shields

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S27 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The acoustical method of measuring energy (EAC), and tangential momentum (TMAC) accommodation coefficients [F. Douglas Shields, J. Chem. Phys. 62, 1248–1252 (1975)] has been used to measure the accommodation coefficients of Ne and He on vacuum flashed Pt and on Pt after exposure to O2, N2, CO, and CO2. Vacuum flashing the Pt at 1400 K in the presence of misch metal getter resulted in a surface that was reproduced a number of times after exposure to various adsorbants. The combined value of TMAC + EAC for this surface was 0.80 ± 0.04 for Ne and 0.64 ± 0.04 for He. These values are significantly greater than values measured earlier in a similar way for W [F. Douglas Shields, J. Chem. Phys. 72, 3767 (1979); 76, 3809 (1982); 76, 3814 (1982)]. Exposing the flashed surface to O2 raised the combined values of TMAC + EAC to 1.28 for Ne and 1.00 for He. Flashing the surface at 1100 K removed some of the O2 and flashing at 1400 K restored the original AC values. In contrast to this, exposure to N2 did not change the surface. Exposure to CO raised the AC values but not as much as O2 but the CO was removed by the 1100 K flash. AC values have also been obtained for N2 on Pt, for O2 on O2 on Pt and for CO on CO on Pt.
FREE

Theory of ultrasonic harmonic generation in hexagonal crystals (A)

Jacob Philip and M. A. Breazeale

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S27 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The expressions for ultrasonic wave propagation in nonlinear hexagonal crystals are derived. Specialization of the equations reveals that in the linear approximation the waves propagate as pure modes in the basal plane and along the symmetry axis. Introduction of the nonlinear terms causes the transverse modes to couple to the longitudinal modes, so that they are no longer pure. Hence, the transverse modes would be difficult to measure. The longitudinal modes, on the other hand, remain pure modes but are coupled to their higher harmonics. Measurement of longitudinal harmonic generation, then, is an interesting possibility. The equations are solved for different directions in the basal plane as well as along the c axis, and expressions are obtained for the nonlinearity parameters in terms of third‐order elastic constants. In the basal plane, the amplitude of the second harmonic is maximum in the [100] direction and minimum in the [010] direction with the average of the two in the [110] direction. Comparison of these results with cubic symmetry is presented. [Research supported by the Office of Naval Research.]
FREE

Pulsed signal distortion in dispersive constant‐group‐velocity media (A)

P. L. Edwards

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S27 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Ultrasonic velocity measurements in solids are often made by measuring the transit times through known distances by short transient pulses. In dispersive and/or attenuative media the signal may be distorted, and the question often arises as to which part, or parts, of the initial and transmitted waves are to be used in the transit time measurement, and just what velocity—phase, group, signal, etc.—is actually being measured. A theoretical and computer study has been made of the distortion undergone by three types of pulses in transmission through nonattenuative dispersive constant‐group‐velocity media, and the effect that this may have on velocity measurements. Theory shows that a pulsed sine wave in such media does not spread out as is normally the case for dispersive media, but repeats itself at definite repetition distances. Computer plots showing the changes that the pulses undergo during transmission will be presented, and how these changes effect velocity measurements will be discussed.
FREE

An acoustic anomaly, sound in a fluid with periodically stratified density and uniform sound speed (A)

Michael Schoenberg and P. N. Sen

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S27-S28 (1982); (2 pages)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The exact solution for harmonic waves in a periodically layered acoustic medium [M. Schoenberg and P. N. Sen, J. Acoust. Soc. Am. Suppl. 1, 71, S44 (1982)] leads, in the long wavelength limit, to some curious results. The most striking is that the equivalent homogeneous acoustic medium is an ideal transverse isotropic fluid. Anisotropy is manifested through the density which must itself be a transverse isotropic tensor! In turn, this leads to the anomalous result that in a stratified medium composed of the same speed c, but different densities, the long wavelength sound speed need not be equal to c. Let ρi be the layer density of the ith layer and let 〈‐〉 denote a thickness weighted average. In the long wavelength limit, propagation perpendicular to the stratification is at a speed c/(〈ρi〉 〈1/ρi〉)1/2 which is less than c. At high frequencies, wave fronts must propagate with speed c in all directions. We examine, over the entire frequency range, the dependence of wave speed normal to the stratification and the alternation of pass and stop bands for such propagation.
FREE

A variational method for wave propagation and scattering in discrete random media: The coherent field for scalar waves (A)

Robert H. Andreo

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S28-S28 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
The propagation and scattering of scalar waves in a random medium of particles is analyzed from a variational point of view. Using an arbitrary set of basis functions, multiple scattering equations are obtained for the multipole coefficients in terms of the single‐particle transition matrix elements and the matrix elements of the Helmholtz‐Green function. Comparison is made with the method of moments and the method of weighted residuals. Closure hypothesis lead to algebraic equations for the coherent scattered field and integral equations for the coherent exciting field. With suitable assumptions on the pair correlation function, dispersion relations can be obtained which characterize the effective macroscopic random medium in terms of an experimentally measurable phase velocity and attenuation coefficient. Examples are discussed, with emphasis on the physical role of the pair correlation function and the mathematical role of the closure hypothesis. [Work supported by NAVSEA and ARO.].
FREE

Frequency dependence of the velocity and attenuation of sound wave propagating in a fluid containing a dense suspension of particles (A)

V. K. Varadan, Y. Ma, and V. V. Varadan

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S28-S28 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
Acoustic waves propagating through a suspension of particles in a fluid are dispersed and attenuated due to two reasons—geometric dispersion or multiple scattering as well as inherent losses if any associated with the particles or the host fluid. A self‐consistent multiple scattering theory is used incorporating the T matrix of the individual particles to characterize their response and a configurational averaging procedure to characterize the statistics of the distribution. Numerical results are obtained for the phase velocity and attenuation of the coherent wave in such a system as a function of the frequency, size, shape, and distribution of the particles of the suspension. These results will be compared with single scattering approximation as well as more approximate methods. The results are of interest in the study of ocean bottom sediments and biological applications.
FREE

Resonance dependence of the dynamic effective properties of particulate composites (A)

G. C. Gaunaurd and H. Überall

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S28-S28 (1982); (1 page)

Online Publication Date: 12 Aug 2005

Full Text: | Download PDF

Show Abstract
We have developed a general deterministic resonance theory for the effective dynamic properties of elastic (or viscoelastic) solids containing ensembles of randomly distributed solid spherical inclusions not necessarily of the same sizes. The method follows our earlier procedure for fluid inclusions [J. Acoust. Soc. Am. 71, 282–295 (1982)] which is generalized here for solid inclusions of known size distributions. We present a summary of the theory and numerous displays of calculations for the effective shear speed, the effective (sound) speed of compressional waves, and the effective attenuation versus ka at known concentrations Φ, or versus Φ at various values of ka. The current theory contains nearly all deterministic results available in the earlier literature and it compares quite favorably, at least within the “acoustical branches,” to the only set of dynamic measurements in the recent literature [i.e., V. Kinra and A. Anand, Int. J. Solids Struct. 18, 367–380 (1982)] which extends sufficiently beyond the long‐wavelength regime to permit comparisons. [H. Überall is also at Catholic University, Washington, DC and is additionally supported by ONR.]
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close