505 



PHOTOGRAPHIC MEASUREMENTS OF THE SIZE, SHAPE AND 

 MOVEMENT OF THE BUBBLE PRODUCED BY 1-OZ. CHARGES 



OF POLAR AMMON GELIGNITE DETONATED UNDERWATER 

 AT A DEPTH OF 3 FEET 



A. R. Bryant 



June 1944 



Summary , 



Msasurements of the size, shape and movement of the bubble produced by i oz. of Polar An»iion 

 gelignite detonated at a depth of 3 feet have been obtained photographically. The measurements cover 

 the first oscillation in detail and a number of typical photojraphs is Included. Tho results are 

 compared with calculations based on the theory of Professor G. I. Taylor, in which the effect of the free 

 surface is also considered. 



The theoretical radius-time curve agrees quite well with the observed mean radius up to the first 



III 

 oscillation, although owing to large energy lossea the minimum radius observed is somewhat larger than i^ 



the predicted value. The downward velocity of the bubble is of the same order as that calculated ^ 



except very near the minumum when the very high calculated values are not attained. The bubble commences "1 



to flatten much earlier than according to the theory of Temperley, and at the minimum is roughly I'' 



hemispherical with a slightly concave upper surfece and a spherical lower surface, like an Inverted »' 



mushroom. £ 



The failure of the bubble to attain the predicted maximum velocity is attributed, at least in 

 part, to the flattening of the bubble. It Is shewn that the vertical momentum in the water is 

 approximately conserved if the effective mass of water moving with the bubble is taken to be a half of 

 that displaced by a sphere whtse radius equals the greatest horizontal radius of tho actual bubble. 



Introduction , 



The purpose of the tests described here was to extend the single flash photographic technique 

 previously used with detonators to l-oz. charges. It was desired to compare the behaviour of the i-oz. 

 bubble with theoretical predictions and to provide data which would assist In interpreting experiments 

 on damage produced by i-oz. charges. 



Experimental Mithad . 



Single photographs of the bubble taken on stationary film were obtained at a scries of times 

 throughout the history of the bubble. The bubble appeared silhouetted against a white painted metal 

 fefloctcr which was illumined by a very bright flash of short duration. The flash was produced by 

 detonating a 2 feet length of C^rotex in a glass tube filled with arg.'n. 



when photographs near the minimum were required the light flash detonator was fired by an 

 electronic switch operated by the pressure pulse produced by the collapsing bubble, suitable time delays 

 being obtained electrically when desired. F^r other photographs a rotary switch with adjustable pre- 

 set contacts fired the main charge, tripped the camera shutter, and fired the light flash at any desired 

 time intervals. In all cases a piezl-electric pressure gauge in the water near the bubble gave a 

 record en a cathode-ray oscillograph fr.m which the timing of the light flash touKi be measured with 

 an accuracy of about 0.O5 milliseconds. All experiments were carried :ut after dark and the shutter 



