39 
402. The fact that the pulse front is spherical and not plane has also been 
investigated and it was concluded that up to the time at which the plete 
leaves the water the assumption of a plane wave is a reasonable approximation. 
Beyond this time, that is when cavitation sets in, the analysis for the 
spherical pulse is also invalid. However, it seems likely that in 
practical cases the curvature of the pulse front will still have little 
effect. In general, it seems probable that the mechanism of transfer of 
energy from water to target envisaged in case 3, involving cavitation and 
follow-up of the water is the most common process for single-hulled ships 
subjected to the pressure pulse from non-contact explosions, especially 
when the conditions are such that appreciable deformation or even rupture 
of the hull occurs. 
Pressure pulse incident on a elding diaphragm in an infinite 
unyielding baffle 
103. A considerable amount of experimental work, both empirical and 
fundamental, has been carried out by using targets consisting of a single 
circular or rectangular air-backed plate to represent a panel of ships' 
plating. In a ship, any one panel of plating dishing under the action 
of the pressure pulse, is restrained from pulling in round its edges by 
the surrounding panels of plating. 
ORUM MODEL BOX MODEL 
WATER 
SG 
\\ 
° 
Fige 19 - Essential features of box and drum models 
Fig. 19 shows a typical single plate target, the air-backed plate BC forming 
one face of a strong bax BEFC. To simulate the resistance of the 
surrounding panels and to prevent damage to the box (which can then be 
used for many experiments) the plate is much larger than the face of the 
box and is fastened by bolts or by welding to a thick rigid baffle 
indicated in section by AB and CD For the present discussion, the 
essential feature of this type of target is that the large surrounding 
baffle is relatively unyielding, being not only very stiff itself but 
also water-backed. The presence of the baffle can modify appreciably the 
transfer of energy from the water to the effective target plate BC. 
Much theoretical analysis has been carried out for such targets but it 
will suffice here to give only the analysis for the simplest assumptions 
Since this serves to bring out the essential differences between this type 
of theory and the infinite plate theory already discussed 
