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ETL 1110-8-11(FR)
15 Jul 91
l. Tussing, Ronald B. 1982 (Jul). "Accuracy
c. For a TNT explosive, the amplitude of the
and Response of Tourmaline Gages for Measurement
direct wave can be estimated from the graph shown
of Underwater Explosion Phenomena," NSWC
in Figure 3 (Cole 1948), in which the abscissa is in
units of "scaled" range (R/W1/3), where R is in feet
TR-82-294, Naval Surface Weapons Center, White
Oak, MD.
and W is the explosive weight in pounds. The water
shock impulse (time integral of the pressure history)
for the direct wave from a TNT explosive source can
3. Water Shock Characteristics
be estimated from the graph shown in Figure 4. The
ordinate in Figure 4 is in units of "scaled" impulse
(I/W1/3), where I is in pounds per square inch-
a. Water shock generated by an underwater
detonation of high explosives travels at a speed of
seconds. Table 1 provides approximate conversion
about 5,000 ft/sec for pressure levels less than
factors for converting several common explosives to
30,000 psi (Cole 1948). In shallow water, the distur-
an equivalent weight of TNT. If the actual value of
bance is characterized by the arrival of four principal
the equivalency factor is unknown, an upper estimate
waves (see Figure 1): (1) an exponentially-decaying,
value of 2.0 will cover most common explosives (i.e.,
direct wave from the explosive source, (2) a surface-
1 lb of explosive is equivalent to no more than 2 lb
relief wave (tensile image of the direct wave), (3) a
of TNT).
bottom-reflected wave, and (4) a wave transmitted
through the bottom materials and radiated back into
d. The approximate value of the water shock
the water (Miller, Strange, and Pinkston 1971). The
pressure (in pounds per square inch), as a function of
effect of these different waves on the resultant pres-
time (t, in sec), for the direct wave is described in
sure history is shown schematically in Figure 2. The
Cole (1948) as:
resultant pressure-time history is the time-phased
superpositioning of the direct, surface relief, reflected,
t
ta
(1)
and refracted pressure waves at a point.
θ
Pme
P(t)
b. For shot geometries where the water surface
and bottom are far removed from the explosion
Where Pm, the peak pressure (in psi) is
source and measuring locations, the direct wave is the
predominant factor.
21,600(λ)
(2)
1.13
Pm
Figure 1. Four principal waves associated with shallow-water explosions
2
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