32 
4 INCIDENT PULSE 
" FROM EXPLOSION 
PLATE 
AIR 
Fige 15 - Pressure pulse incident on 
unit area of infinite plate 
where € 
mn 
86. For the simplest case, the 
pressure pulse arrives at normal 
incidence and the explosion is 
sufficiently far away for the 
pulse to be treated as a plane 
wave. Every element in the 
plane plate then behaves in the 
same way and attention can be 
fixed on unit area. The 
incident pressure pulse from the 
explosion will then give rise to 
a reflected pulse, the form and 
magnitude of which will depend 
on the motion of the plate. 
Fig. 15 shows the pressure pulse 
incident on unit area of 
infinite plate. Expressions 
for the displacement of the 
plate and the pressure on it are 
derived at Appendix C where it 
is shown that if 
peler fessor) Meestl 150) 
wade Paice pistes salad) 
+ = time measured from the first arrival of the pulse at 
the plate 
x = displacement of plate 
k = resistance to motion for unit area per unit displacement 
of the plate 
P, = pressure in incident pulse 
Pp, = pressure in reflected pulse 
Pp = pressure on plate 
Pp, = maximum pressure in incident pulse (at time t = 0) 
u, = particle velocity due to the incident pulse in water 
touching plate 
u, = particle velocity due to the reflected pulse in water 
touching plate 
f = mass density of water 
c = velocity of sound in water 
m = mass of plate per unit area of surface 
n = exponential parameter determining rate of decay of pressure 
2p, 
Then x = eee Gnlseee -fe 
mn (€-1)€ 
2Po -nt ent 
P = P+ = e -6 
Brie. qicisis ences (32) 
