330 



THEORY OP UNDERWATER EXPLOSION BUBBLES 



Introduction 



The theory of the behavior of a gas bubble produced 

 by an underwater explosion has reached such a state of 

 completeness that it seems desirable to give a unified 

 account of some of the main results. When an explosive 

 is detonated under water, a shock wave is first emitted 

 and then the gaseous products of the explosion expand 

 ^ande^ the influence of their high internal presstire. Be- 

 cause of its inertia, the gas bubble overexpands to a 

 very low pressure and then the hydrostatic pressure of 

 the water recompresses the bubble to nearly its original 

 size. At this stage the bubble starts expanding again 

 and a pressure pulse is emitted. This process of expan- 

 sion and contraction may occ\ir five or six times before 

 the bubble breaks up and dissolves or escapes from the 

 water. 



The behavior of the bubble is affected by the pres- 

 ence of surfaces, such as the bottom of the water, the 

 walls of a tank, the tsirget or the air-water surface. 

 Normally, the bubble would tend to move upward since it 

 is lighter than the surrounding water. However, the free 

 siirface of the water repels the bubble while a rigid sur- 

 face of any kind such as a wall or a bottom attracts it. 

 In some cases these effects may be so strong that the 

 bubble actxially moves downward. 



Besides influencing the motion of the bubble, the 

 siirfaces also change the period of oscillation and modify 

 the size of the peak pressures produced. The theory 



