248 



-2- 



long); so that the moraentura imparted and the destruction 

 caused may be comparable to that of the first shock. The 

 importance of the second pulse has been confirmed more and 

 more not only by model experiments, but also by analysis 

 of actual damage to allied ships by mines [1], [2]» 



Just as significant as the long duration of the sec- 

 ond pressure pulse, is the migration of the gas bubble 

 during the pulsation. The migration can increase the effect 

 of the second pressure pulse because, vmder suitable conditions, 

 the center of this pulse might be much closer to the target 

 than the explosion. Factors influencing the motion of the 

 bubble are: rigid walls such as the hull of a ship or the 

 sea bed, which attract the bubble; the free surface of the 

 water, which has a repulsive effect; and the buoyant force 

 of gravity, which causes the bubble to rise towards the sur- 

 face. 



Understanding and controlling the complicated inter- 

 play of these effects is of sufficient practical importance 

 to warrant comprehensive research. Unfortunately, a great 

 variety of experiments with full size charges is hardly 

 feasible, and experiments with small charges cannot easily 

 be reinterpreted for large charges. Such difficulties call 

 for theoretical investigation as a guide to experiment. 



Historically, the earliest theoretical problem, satis- 

 factorily analyzed in older studies, is that of a single 

 spherical gas bubble Immersed in an infinite body of water; 

 in particular, the pressure as a function of time and distance, 

 and the period of pulsation of the bubble can be explicitly 

 detennined. 



For the past few years an extensive research program 

 on underwater explosions has been pursued by G. I. Taylor 



* Bracket references refer to the bibliography. 



