A History of Research and a Review of Recent Developments

50
Figure 2.18 Radius/time curve of the gas sphere for 0.55 lb of Tetryl detonated 300
ft below the surface (from Swift, ref. 2.30).
latter work. Note that the reversal of the bubble motion is virtually
instantaneous and discontinuous. A comparison of radius and period, and
the formulation of a simple analysis, had been made much earlier by Ramsauer
[2.31] in 1923. He determined the position of the gas bubble boundary by
means of an electrolytic probe, when charges of gun cotton weighing one or
two kilograms were exploded at depths up to 30 feet in 40 feet of water.
Although he could only measure the radius of the bubble and the time for
isolated points, nevertheless it was a very useful and innovative study. He
found that the variation of maximum bubble radius with depth could be
predicted by the formula
(2.17)
where p 0 is the hydrostatic pressure at the depth of the explosion, W is the
weight of explosive and a m is the maximum bubble radius.
Photography, however, enabled a much more detailed picture of bubble
behaviour to be drawn, and using Edgerton’s results, Ewing and Crary [2.32],
scientists from the US Woods Hole Oceanographic Institution, were able to
plot curves of the type shown in Figure 2.19, and compare them with calculations
by Herring [2.33] in 1941 based on the following formula for the first period
of oscillation (T) of the bubble:
where ρ 0 is the equilibrium density.
The detonation of explosive charges
(2.18)