Figure 17. Rise of the Bobble from a Deep Explosion. Charge: 1.1 lbs TNT. Depth: 4—8 maximum 



bubble radii. 



bubble can already be seen through the water. At this time the bubble has virtually 

 ceased to oscillate and had probably the shape of a mushroom head. It is a relatively 

 rare incident that the bubble stays together in this manner. Usually, it dissolves into 

 many tiny bubbles and a sort of soda water appears on the surface. We have here again 

 an interesting hydrodynamic problem, namely the motion and the stability of a large 

 gas-volume under water. (See contribution of Lane and Green in reference [23].) 



Some Hydrodynamic Problems of the Damage to Structures 



We proceed now to the problem of damage done by underwater explosions to 

 idealized structures. We will not discuss military applications of underwater explosions 

 against actual ships or submarines, but will restrict ourselves to hydrodynamic aspects. 



The Reloading of an Air-Backed Plate 



It was mentioned that about 50 per cent of the total chemical energy of the 

 charge is found in the energy of the bubble. Therefore, the question arises as to whether 

 this large energy term contributes to the damage, for instance to the deflection or 

 rupture of a plate. Schauer [19] has treated this question and he pointed out that, 

 according to experiments, the initial deflection of an air backed plate takes place in two 

 steps, as illustrated in Fig. 18. The second blow is neither caused by the bubble pulse 

 which comes much later and produces a further deflection, nor by the Shockwave, 

 because at this time the Shockwave has long disappeared. Also, the total deformation 

 energy of the plate is larger than the energy flux of the Shockwave impinging on the 

 plate. It turns out that this second blow is caused by the expanding bubble by means 

 of the following mechanism: 



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