885095950

tions one of two modds for bubble dynamics will be employed: the Gilmore-Akulichcv formulation with temperaturę estimated polytropi-cally or Flynn’s equations in which temperaturę is calculated exactly. [Work supported by NIH and ONR.] in the liquid. This formulation does not require the assumptions madę in the classic theory of Ellcr and Flynn [J. Acoust. Soc. Am. 37, 493-503 (1965)]. In some conditions results indicate a significant differcnce in growth ratę predictions when compared to the Eller-Flynn model. [Work supported by NSF.]

9:30

2PA5. Nonlinear pulsations of cavitation vapor bubbles near resonance. R. Edward Nicholas and Robert D. Finch (Dcpt. of Mech. Eng., Univ. of Houston, Houston, TX 77204-4792)

Studies of the nonlinear pulsations (and sometimes collapse) of cav-itation bubbles near resonant size in an ultrasonic field were performed through a numerical solution of nonlinear equations describing the mo-tion of a sphericał vapor bubble. A number of plots are presented show-ing bubble pulsations. These plots show pulsations at the driving fre-quency with rich harmonie content but also show nonchaotic pulsations at frequencies below the driving frequency as the bubble grows through resonant size. The frequencies observed below the driving frequency seem unrelated to the driving frequency and instead vary with the amplitudę of the ultrasonic field.

9:45

2PA6. SignaJ Processing to, extract transient microcavitat(on signals from noise. Qihong Xu, Christy K. Holland, and Robert E. Apfel (Dept. of Mech. Eng., Yale Univ., New Haven, CT 06520)

The time history of the scattcred signal from transient microcavita-tion is different from the signal scattered by other targets, which con-stitutes most of the noise. The backscattered signals from transient mi-crocavitation (bubbles of micron scalę that last on the order of microseconds) are both frequency modulated and amplitudę modu-lated; therefore, a Doppler technique can be one altemative to the de-tection of transient cavitation, which takes advantage of the fact that the signal is frequency modulated. Numerical simulations of these Processing techniques will be presented. [Work supported by NIH Grant 5R01CA39374.)

lfcOO

2PA7. An experimental test of a theory of nonlinear bubble dynamics. Darren L. Hitt, Andrea Prosperetti (Dept. of Mech. Eng., Johns Hopkins Univ._f Baltimore, MD 21218), and Ronald A. Roy (Natl. Ctr. for Physical Acoust., Univ. of Mississippi, University, MS 38677)

Nonlinear bubble oscillations in a levitation celi are studied. The experimental levitation number. L< = pg/\ Vp), can be compared to its corresponding theoretical value to provide a sensitivc eva!uation of the bubble dynamics theory [Prosperetti et a/.. J. Acoust. Soc. Am. 83, 502-514 (1988)). A pulsc-echo technique is developed that permits extremely accurate measurements of the bubble location in the pressure field. This technique can then be used to obtain accurate measurements of the levitation number under a varicty of expcrimental conditions. (Work supported by NSF.)

10:15

2PA8. Rectified diffusion during nonlinear gas bubble oscillations. Vinod Kamath and Andrea Prosperetti (Dept. of Mech. Eng., Johns Hopkins Univ., Baltimore, MD 21218)

Mass transfer of the dissolved gas across a bubble wali during nonlinear spherically symmetric oscillations is studied. Usc of an earlier comprehensive model [Prosperetti et al._t J. Acoust. Soc. Am. 83, 502-514 (1988)] to determine the bubble dynamics avoids the need to use ad hoc polytropic assumptions. A numerical technique based on a pseu-dospectral method is used to determine the dissolved gas concentration

1863 J. Acoust. Soc. Am., Vol. 89. No. 4, Pt. 2, April 1991

10:30

2PA9. Nonlinear oscillations of gas bubbles in elastic solids. Paul B. Massell (Automation Counselors, Inc., 650 Americana Dr., Annapolis, MD 21403) and Gary Albin (Naval Med. Res. Inst., Bethesda, MD 20889-5055)

This work was part of a project whose long-range goal is the devel-opment of a device for estimating the size of bubbles in human tissue. Calibration standards are expected to consist of gas bubbles in polymer gels. Accordingly, equations in Prosperetti [J. Acoust. Soc. Am. 56, 878-885 (1974)] that describe forced oscillations of a gas bubble in a liquid have been modified to apply to the case of a gas bubble in a linearly elastic solid. The changes in the analytic expressions for the resonance Solutions are modest, and the major features are preserved (e.g., hysteresis for main, subharmonic, and harmonie frequency re-gions). Morę precise equations for the liquid case in Kamath and Prosperetti [J. Acoust. Soc. Am. 85, 1538-1548 (1989)] have also been modified to treat the elastic solid case. Following these authors, a Galer-kin spectral method was used to generate numerical Solutions to the goveming partial diffcrential equations. Situations in which two or morę stable Solutions exist for a given set of parameters may be discussed.

10:45

2PA10. Experimental studies of the enhanced effective nonlinearity parameter B/A of a bubbly medium. Junru Wu and Zhemin Zhu (Dept. of Physics, Univ. of Vcrmont. Burlington, VT 05405)

It has been known for some years that the presence of bubbles may enhance the nonlinearity parameter B/A of a medium. Two distinct physical mechanisms are bclicved to be involved. The first one is due to bubble nonlinear oscillations; bubbles are driven by an acoustic wave near resonance frequency. The second one is due to static properties of a bubbly medium. The cffective nonlinearity parameter B/A of water containing a three-dimensional ensemble of randomly distributed uniformly-sizcd trapped cylindrical bubbles was measured. The mea-sured effective B/A for the system is of the magnitude of 10⁴ to 10⁵. The experimental results also suggest that the dramatic cnhancement of the effective nonlinear parameter B/A is mainly due to the nonlinear resonance oscillation of the trapped bubbles. [Work supported by the NIH via Grant No. CA42947 and by the NSF and Ycrmont Epscor.]

11:00

2PA11. Calculations of temperaturę within and without a pulsating gas-filled carity. Charles G Church (Natl. Ctr. for Physical Acoust., Coliseum Dr., Univ. of Mississippi, University, MS 38677)

The temperaturę of the gas within a sphericał cavity driven by a sinusoidal pressure field is calculated using an existing model [H. G. Flynn, J. Acoust. Soc. Am. 57, 1379-1396 (1975)] for cavitation dynamics. The temperaturę field in the liquid surrounding the bubble also is calculated with this model. For this work it is assumed that temperaturę variations are due to heat conduction only, although corrections for evaporation, condensation, etc., may be included if desired. Because the temperaturę Tin the liquid at the caviiy interface is allowed to vary (which reduces heat conduction by rcducing the thermal gradient at the interface) the efTect of holding T fixcd is investigated. Results are presented for argon-filled and air-filled cavities in water or various organie liquids. [Work supported by ONR and NIH.]

121 st Meeting: Acoustical Society of America 1863