there is a strong bubble migration and therefore also an inversion of the bubble. The 

 spike or pressure jump is probably caused by the water hammer effect of the colliding 

 bubble surfaces. (The oscillations which suddenly appear shortly after t = 0.5 T are 

 caused by the reflection of the Shockwave from the bottom of the sea.) 



If we explode a small charge in a very great depth (say 1 lb. in 500 ft.) the 

 period of bubble oscillation is so small that the gravity or buoyancy cannot produce 

 any significant bubble migration. The shape of the bubble pulse from such a non- 

 migrating bubble is indicated by the dotted line in Fig. 7. It is smooth, without any 

 irregularities and shows a somewhat higher pressure. Apparently no inversion of the 

 bubble takes place here and the bubble contracts to a smaller volume. Underwater 

 photographs have shown indeed that a non-migrating bubble does not change its shape 

 but remains spherical over many pulsations until it finally dissolves into many little gas 

 bubbles. 



1st Cycle 

 19% Shockwave 

 35% Dissipated 



2nd Cycle 



2 5% Pulse 



37. 5% Unaccounted for 

 37. 5% Bubble 



U 



c 



>s 



u 



4) 



100% 



50% 



Pulse 



Unaccounted 

 for 



Bubble 



"oH o77 



0.2 



MIGRATION AZ/Z 



Figure 8. Energy partition of an underwater explosion. The upper portion refers to a non-migrating 

 bubble. The energy distribution of the 2nd cycle is that found after the first bubble minimum. 

 This distribution is affected by the bubble migration as shown in the graph. AZ is the migration 

 between the first and second bubble maximum, Z, the total hydrostatic head at the depth of 

 explosion. 



334 



