378 



DIGEST* 



The gas globe formed by an underwater explosion not only pulsates 

 in size but also usually changes position as each pulsation occurs (1).** 

 This migration may be of importance because the first recompression or con- 

 traction of the globe thereby comes to be centered at a point different from 

 that of the initial detonation, and the location of the point of recompres- 

 sion influences the damage that may be done by the associated secondary pulse 

 of pressure. 



Accurate solution of the general equations of the motion of the gas 

 globe set up by Herring (4) in this country and by G.I. Taylor and others (5) 

 (6) (7) (8) in England is, in general, possible only by numerical solution of 

 the differential equations; it has not yet been found possible to embark on 

 such an enterprise in this country because of the labor involved. For pur- 

 poses of analysis, calculations of the motion of the gas globe have been made 

 by an approximate method. The assumptions underlying this method are set 

 forth in the first part of the report, 

 together with a discussion of the ap- 

 parently conflicting and paradoxical 

 motions of the gas globe under various 

 conditions. 



For example, in free water of 

 unlimited extent the gas globe rises be- 

 cause of its buoyancy. Near a rigid 

 boundary such as a vertical wall, the 

 globe is attracted toward the boundary, 

 as shown in Figure 2. Near the surface 

 of the water, the gas globe is repelled 

 from the free surface. However, although 

 the action of gravity is always present 

 to cause the globe to rise through the 

 water by virtue of its buoyancy, the at- 

 traction of a rigid bottom in shallow 

 water, or the repulsion from the free 

 surface of the water, may decrease the 



0.01 0.02 0.03 0.04 0.05 

 Time in seconds 



Figure 2 - Curves of Size and 



Position of a Gas Globe 



near a Vertical Wall 



The charge was fired 9 inches from a rigid 

 vertical wall. Note that the velocity of 

 the center of the globe is greatest during 

 the compression phases. 



* This digest is a condensation of the text of the report, containing a description of all essential 

 features and giving the principal results. It is prepared and included for the benefit of those who 

 cannot spare the time to read the whole report. 



Nxmbers in parentheses indicate references on page 33 of this report. 



