31 
INTERACTION BETWEEN TARGET AND WATER PHENOMENA DUE TO 
NON-CONTACT EXPLOSIONS 
83. So far in this chapter, the explosion has been assumed to take place 
in open water with no target present and attention has been concentrated 
on the resulting pressure in the water, However, the presence and 
behaviour of the target modifies this pressure so that it is not possible 
to make the simple assumption that the target is subjected to the 
pressure which would occur in the absence of the target. The important 
and rather difficult problem of the interaction between target and 
explosion effects must, therefore, be considered 
8. First, the effects associated with the pressure pulse will be 
studied. Existing theories for the interaction between the pressure 
pulse and a target have followed two basic lines depending on two 
different simple types of target:- 
(4) the target is assumed to be plane and of infinite extent 
but capable of yielding. 
(2) the target is considered to be plane but only a finite 
area is assumed to yield, the remainder cf the target 
being fixed and rigid 
In general, the first type of theory is more relevant to actual ship 
targets whilst the second type of theory is especially relevant to 
special types of single-plate targets used in small-scale research 
Pressure pulse incident on infinite plane air—backed plate 
85. The dimensions of actual ship targets are usually large compared with 
the effective length of the pulse and the curvature of the ship's plating 
is small, Therefore, it is not unreasonable to regard the hull plating 
to be an infinite plane platee As a further simplication, the 
resistance to deformation of the hull is represented by a resistance 
distributed uniformly over the plane area, the movement of any element 
of area being opposed by a force proportional to displacement™ of the 
element. 
Such a resistance is usually associated with an elastic spring but, 
as explained later, this linear relation holds also for plastic 
stretching of a plate; it is the latter rather than the former which 
is being simulated, since elastic deformation itself involves no 
permanent damage. 
