652 



The method of obtaining a value of Pjjj for Vq • which is most 

 imiversally applicable is the measurement of the greatest periphery 

 attained by any dome from successive high speed photographs of the 

 underwater explosion. It is assuued that at the edge of the dome, 

 the vertical component of the pressure is the critical value, below 

 which water does not leave the surface. The calculation can be readily 

 understood by reference to Fig,. 16 and the vector diagram giving T/2 

 from ?g^ and the angle °<. , It is obvious that we need the weight of the 

 charge, the depth R, some means of obtaininjg a good vsilue of P^, and a 

 knowledge of the geometry of the system so that we can calculate D, 

 the greatest dome diameter, from the photographic image. Unfortunately, 

 this sort of calculation could not be applied to any of the work pre- 

 sented in this report because the photographs were taken at short 

 distances to obtain the best value of Vq at the center of the dome and hence 

 did not Include the complete phenomena. However, many suitable photographs 

 have been taken in this laboratory during the course of other work wr»^ 

 this calculation has been made for a representative number of shots. 

 Large charge experiments were used to get an estimate of T from full scale 

 work in the open sea for comparison with the other values presented which 

 were obtained largely from laboratory scale explosions. These calcu- 

 lations are summarized • in Table VIII. 



TABLE VIII 

 APPROXIMTE VALUE OF T OBTAINED FROM DOME PERIPHERY CALCULATION* 



T 

 (lb/in. 2) 



360 

 480 

 880 

 400 

 380 

 360 

 360 

 AlO 

 340 

 460 

 450 

 400 

 480 

 500 

 500 

 310 

 320 

 540 

 460 



* Charge equivalent to 325 lb TNT, 



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