• 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

May 1988

Volume 83, Issue S1, pp. S1-S122

Return to All Sections
back to top
RSS Feeds
back to top Session AA. Physical Acoustics IV: Miscellaneous Topics in Physical Acoustics
Contributed Papers
FREE

Evolution of unstable disturbances at a mean‐flow stagnation point (A)

Charles Thompson and Martin Manley

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S57-S57 (1988); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
The interaction between infrasonic, acoustic disturbance and the mean flow near the stagnation point of a bluff body will be examined. The criterion for stability and intermodulation of the disturbances will be discussed. The spatial and temporal evolution will also be addressed. It will be shown that infrasonic and unstable vortical disturbances, working in conjunction, can serve to modulate the amplitude of the acoustic wave. For a harmonically time‐varying acoustic wave, this modulation is manifested in an increase in the spectral bandwidth of the wave. [Work supported by Analog Devices Professorship.]
FREE

Effect of internal relaxation on the optoacoustic signal in CS2 (A)

Charles Thompson, Henry E. Bass, and Richard Raspet

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S57-S57 (1988); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
The optoacoustic signal in CS2 has been observed using an experimental configuration similar to that of Sullivan and Tam [B. Sullivan and A. C. Tam, J. Acoust. Soc. Am. 75, 437–441 (1984)] and has been compared to theory and similar results in propanol. The comparisons illustrate that an internal relaxation process is affecting the observed waveform. Assuming a simple three‐level system for internal energy and using independently measured vibration‐to‐translation transfer rates leads to the conclusion that the relaxation process observed is associated with electronic‐to‐translation or electronic‐to‐vibration energy transfer with a relaxation time of 90 ns. [Work supported by the Office of Naval Research.]
FREE

Photoacoustic method for measuring high‐order multiphoton absorption in transparent materials (A)

Scott C. Jones

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S57-S57 (1988); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
A photoacoustic technique for measuring multiphoton absorption from sharply focused pulsed laser beams is developed for arbitrary order of nonlinear absorption. The resulting sound source is neither spherical nor cylindrical, and a multipole expansion is presented through quadrupole terms for thermal and electrostrictive source terms. The analysis shows that the acoustic amplitude is proportional to absorbed energy, and proportional to the mth power of incident laser energy under conditions of m‐photon absorption. The calibrated measurement of the four‐photon absorption cross section of NaCl at wavelength 532 nm is presented. [Work supported by NSF.]
FREE

Acoustic imaging by a method of image projections (A)

Daniel Rouseff, Robert P. Porter, and Leung Tsang

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S57-S57 (1988); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
A method of three‐dimensional acoustic imaging based on image projections is derived. A weakly scattering object is illuminated by a plane wave and the scattered field is recorded. Inversion methods based on projections that operate directly on the scattered field are inaccurate due to diffraction effects. By backpropagating the scattered field onto a plane in the image region, diffraction effects are reduced and a projection of the object is generated. Conventional x‐ray inversion techniques may then be used to image the object. The relationship between the backpropagated field and the projection is derived both for high‐frequency incident waves and low spatial frequency scatterers. Backpropagation additionally allows the use of curved or misaligned recording surfaces. [Work supported by ONR.]
FREE

Propagation of sound in vibrationally excited N2/He, N2/H2, N2/CH4, and N2/H2O mixtures (A)

F. Douglas Shields and L. Dwynn Lafleur

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S58-S58 (1988); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
Previous measurements of resonant reverberation of sound in N2/H2 mixtures in a closed tube have shown an amplification of the sound following the rapid excitation of the gas by an electric discharge [J. Acoust. Soc. Am. 81, 87 (1987)]. These measurements have been extended in this paper to include N2/He, N2/CH4, and N2/H2O mixtures. Some of the excessively large amplification previously observed in N2/H2 mixtures has now been attributed to nonlinearity in the microphone response. However, even after correcting this error the amplification is much larger and lasts for a longer time than theoretically predicted. The variation in the translational temperature following the discharge is monitored by measuring the sound velocity. Relaxation times determined from the temperature versus time curves differ only slightly in magnitude and/or temperature dependence from previously reported values. [Work supported by ONR.]
FREE

Instability and particle agglomeration in acoustically driven flows (A)

Charles Thompson and Vineet Mehta

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S58-S58 (1988); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
The mechanism responsible for instability and turbulence generated by high amplitude acoustic waves has been of interest of in acoustic agglomeration of particles. When a low‐frequency oscillation is used in conjunction with a higher frequency acoustic wave, localized unstable boundary layer disturbances can be used to drive the outer flow field. By virtue of the Reynolds stress, the harmonic spectrum of the unstable vortical disturbance serves to modulate the acoustic wave amplitude. This process enhances the ability of the acoustic wave to agglomerate particles. A theoretical model of the instability mechanism and the interaction process will be presented. [Work supported by Analog Devices Professorship.]
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close