### ASA 126th Meeting Denver 1993 October 4-8

## 2pPA10. Effect of microbubbles on self-similar waterborne shocks.

**B. Edward McDonald
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*Naval Res. Lab., Washington, DC 20375
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Similarity solutions developed from the equations of nonlinear acoustics
[P. H. Rogers, J. Acoust. Soc. Am. 62, 1412--1419 (1977); B. E. McDonald and J.
Ambrosiano, J. Acoust. Soc. Am. 84, 1497--1503 (1988)] have adequately
accounted for the range dependence of overpressures in the propagation of
underwater spherical shocks, while giving only fair to poor predictions for
relaxation time constants at large ranges from the source. The relaxation time
discrepancy seems to suggest an anomalously large nonlinearity coefficient at
great distances from the source. The effect of minute quantities of entrained
air on the shock similarity solution for water is investigated. It is well
known that microbubbles can greatly increase the nonlinearity coefficient of
water at ambient conditions. At high pressures, however, bubbles may collapse
to the point of being dynamically unimportant. The equation of state for water
is modified to account for ambient microbubble populations, and the resulting
equations solved for self-similar shock profiles. Using air void fraction as a
fit parameter, observed relaxation time data are analyzed to yield the levels
of entrained air that may have been present in various underwater explosive
experiments.