Environmental Engineering Reference
In-Depth Information
2.4.4.2 The Explosion Shock Waves of Liquid Explosives Under Water
When the packed explosives explode in unlimited, uniform, and static water, the
rapid expansion of explosion products
first induces the formation of shock waves,
which is followed by the generation of sparse waves by explosion products on the
intersurface of products and water. The sparse waves propagate to the center of
products, which is the reverse of shock waves. The pressure of original shock
waves in water is much larger than that in air. For example, when the pressure of
original shock waves in air is 80
130 MPa, the pressure of original shock waves in
water is larger than 10,000 MPa. In the propagation of shock waves in water, both
pressure of wave fronts and velocity/rate drops down faster. And the waves are
broadened continuously. For the shock waves from explosion of spherical liquid
explosives, their pressure decreases rapidly within 1
-
c
0
. The pressure is only 1/
100 of the original one. Figure
2.46
gives the measured shock wave pressure
changes within different distances from the explosion of 100 kg hydrazine nitrate
liquid explosives.
Figure
2.46
shows that the pressure drops faster when it is close to the explosion
center; while the pressure drop slows down once it is far from the explosion center.
In addition, in the explosion of liquid explosives under/in water, the positive impact
time of shock waves is longer following the distance increasing, but it is much
shorter than that of air shock waves. The impact time in water is only about 1/100
of that in air because the speed difference between fronts and tails is smaller in
water. For example, when the pressure of water shock waves is P = 500 MPa, the
velocity/rate of water shock waves is 2,040 m/s (when the pressure of water shock
waves is 5 MPa (1/100 of water), the velocity of air shock waves is 2,230 m/s).
When the pressure drops down to 25 MPa, the propagation velocity of water shock
waves is close to sound rate (about 1,450
1.5
-
1,500 m). Now the fronts and waves have
-
similar propagation rate.
The above-discussed shock waves are in unlimited water medium. The real
water medium has free surface (intersurface of water
air) and water bottom. After
the explosion of liquid explosives, the shock waves in water reach the free surface
or water bottom, and then re
-
ection is generated.
(1) Existence of free surface
When the water shock waves reach the free surface, there is a dark gray
hydrosphere expanding rapidly on water surface. Its migration velocity is very
large. This hydrosphere disappears several milliseconds later. The re
fl
ection of
shock waves occurs on the free surface. According to the condition that the pressure
is close to zero after the incident and re
fl
fl
ective waves converge together, the
re
ective waves are sparse waves. (Because the acoustic impedance of water is
much larger than that of air, according to the propagation theory of stress waves in
different media, the re
fl
ective waves are sparse waves) Under the effect of sparse
waves, the water particles/drops are splashed further up, and a special splashed
water mizutsuka is generated. Later, the water bubbles of gas products arrive on the
water surface, and a splashed water column is formed. The gas bubbles reach the
water surface before they start contracting. Because the gas bubbles
fl
