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people, has in the last 30 years had a suddcn, explosive, and unsettled growth. Con$equcntly, the city is always attacked by an endless number of noise sources. The absence of requirements for acoustic planning has caused noise producing activities to be mixed in with buildings requiring a quiet sonie environment. This study analyzes the main community noise sources and their lcvels: traffic and transportation noise, aireraft, and industrial noise. The noise pollution levels obtained, which were calculated through theoretical form u las and cmpirical methods, arc plottcd in noise maps of the metropolitan area of Lima. Unfortunately, Peru does not have an acoustical research center, laboratories in acoustics, or professional researchers in acoustics. The results of this research allowed comparison of the average levels calculated, around 92 dB in the downtown area, in regard to requested noise levels. The lack of legislation, acoustic research, and people's knowledge about noise dam-age will lead to its progressive inerease, almost 1 dB per year, in the near futurę.

CARROLL, 8:30 TO 11:30 A.M.

TUESDAY MORNING, 30 APRIL 1991

Session 2PA

Physical Acoustics: Bubbles and Drops

Charles C. Church, Chair

National Center for Physical Acoustics, Coliseum Driue, Uniuersity, Mississippi 38677

Contributed Papers

8:30

2PA1. Study of surface dynamics of drops in the presence of surfactants. Yuren Tian, Glynn Holt, and Robert E. Apfel (Dept. of Mech. Eng., Yale Univ., 2159 Yale Station, New Haven, CT 06520)

The characteristics of capillary waves, especially energy dissipation, are strongly influeneed by the presence of surfactants. The phenomenon has been studied by investigating experimentally the free quadrupole oscillations of a fluid drop acoustically levitated in the air. The experi-mental apparatus is similar to that of Trinh [Rev. Sci. Instrum. 56, 2059 (1985)], and the methods follow those reported by Lu and Apfel [J. Colloid Interface Sci. 134(1), 245 (1990)]. Using this system, the fre-quency of free quadrupole oscillations and its damping constant can be measured. Watcr drops with different sizes and different surfactant con-centrations were used in the measurements. Experiment results show that the technique used here, which is nonperturbative and requires a very smali amount of sample, may supplement other methods to mea-sure the surface properties of liquid. (Work supported by NASA through JPL, Contract 958722.]

9:00

2PA3. Collapse of a long cylindrical bubble. Jorge E. Lopez de Cardenas (Schlumberger Perforating Ctr., 10910 Airline Rd., Rosharon, TX 77583) and Robert D. Finch (Univ. of Houston, Houston, TX 77204)

The collapse of a cylindrical bubble was modcled using an approach similar to Rayleighk solution for a sphcrical bubble. Rayleigh assumes an incompressible fluid, which, in the cylindrical case, leads to the problem of the fluid having infinite kinetic energy. To overcome the difliculty a ‘‘scmi-compressible" assumption is used, in which only the fluid containcd in the acoustic cnvelope defined by r = ci is considered in the solution; the fluid outside this envelope being neglected. The results obtained with this approach were compared with Solutions com-puted from a model using a finite element method. As in Rayldgh’s solution for the spherical bubble, the calculations of the collapse time for the cylindrical bubble showed very good agreement with the numer-ical Solutions. The results obtained for the pressure generated by the collapse of the cavity provide a qualitative description of cavitation eflccts produced by jets from shaped changes.

8:45

2PA2. Stimulation of drop coalescence with acoustic cavitatk>n. Edward A. Gardner and Robert E. Apfel (Dcpt. of Mech. Eng., Yale Univ., Box 2159 Yale Station, New Haven, CT 06520)

A standing acoustic field was used to levitate a pair of anisole (meth-oxybenzene) drops in an aqueous surfactant solution containing Teflon particles to act as cavitation nuclei. The drops were brought into contact with each other by the levitation field but did not coalesce immcdiately becaase of the surfactant in the water. By inereasing the intensity of the sound field, cavitation events were produced, some of which ruptured the oil/water interface, causing plumes of micron-sized oil droplets to be expelled from one of the main drops. Occasionally, this disturbance caused the main drops to coalesce. This method of stimulating coalescence was studied using high-speed film and statistical analysis, which will be reviewed in the presentation. (Work supported by NASA through JPL, Contract 958722.]

1862 J. Acoust. Soc. Am.. Vol. 89, No. 4, Pt. 2. April 1991

9:15

2PA4. A comparison between “real” and “ideał” gas in theoretical cavitation dynamics. Charles C. Church (Natl. Ctr. for Physical Acoust., Coliseum Dr., Univ. of Mississippi, University, MS 38677)

Most theoretical formulations for the response of smali gas bubbles to acoustic pressure fields assume that the ideał gas equation of State is appropriate for calculating the intemal pressure of the bubble. While this assumption is adequate at Iow amplitudes, at higher pressure am-plitudes, and thus larger bubble responses, it leads to predictions of intemal gas densities that are on the order of, or greater than, those of metals. A morę realistic assumption is a van der Waals equation of stale for a “real*’ gas. In the present work a generał expression for the pressure inside a bubble containing real gas is provided, as well as expres-sions resulting from some common simplifying assumptions. In addi-tion, comparisons between calculated bubble responses using either an ideał gas or van der Waals equation are presented. For these computa-

121 st Meeting: Acoustical Sodety of America 1862