Figure 9. Bubble Behavior of an Explosion on a Rigid Surface. The charge was fired on a steel plate. 

 „ The water surface is visible near the top of each frame. 



tion due to gravity. Fig. 9 shows an explosion on the bottom. The attractive action of 

 the bottom is clearly visible. The bubble seems to cling to the bottom, but the effect 

 of gravity is stronger and finally tears the bubble away. The repulsive effect of the 

 surface is not noticeable here, because of the strong upward momentum of the bubble. 

 In the test shown in Fig. 10 a rigid cylinder has been mounted under water. 

 Frame 1 shows the bubble maximum. In frames 2 and 3 the attraction force of the 

 cylinder becomes apparent. Frame 4 shows that the bubble has not migrated straight 

 upward but toward the solid body in the water. 



Surface Phenomena 



The Spray Dome 



When the Shockwave strikes the water surface, the air-water interface becomes 

 highly unstable. It breaks up into many spikes or needles which quickly disintegrate 

 into droplets. According to the mathematically treatment of G. I. Taylor [16] the 

 original irregularities grow exponentially with time. This is nicely seen in Fig. 11. (Test 

 made by Young and Goertner, NOL.) The jets spring up predominantly from the crests 

 of the ripples which were there before the explosion. This phenomenon is of particular 

 interest, since one can determine the peak pressure of the Shockwave photographically 

 by measuring the initial velocity of the spray dome. However, the spray which is 

 emitted from the peak of an irregularity moves faster than the average and this may 



336 



