SECONDARY PRESSURE WAVES 



385 



fired at various depths in 24 feet of water. Only a few of the results, 

 which were not completely analyzed at the time of writing, are given 

 here. 



The peak pressure and positive impulse for 50 gm. tetryl charges are 

 plotted in Fig. 9.7. The peak pressures show a pronounced maximum 

 near the upper rest position (measured experimentally as described in 

 section 8.11 and indicated by the vertical line). The calculated theo- 

 retical value for the first pulse of 430 Ib./in.^ at this depth and gauge 

 distance of 3 feet (from Eq. 9.12) is comparable with the experimental 



-3 



-2 



-I 



TIME (msec) 



Fig. 9.6 Observed and calculated bubble pulses for a one ounce Polar Ammon 

 Gelignite charge fired six feet below the surface. 



value of 600 Ib./in.^. There should also be a lower rest position of maxi- 

 mum peak pressure at about 20 feet, but this region was not measured 

 in suflacient detail to reveal it for this charge weight. The impulse 

 curves show less pronounced maxima and curves computed from Eq. 

 (9.25), included for comparison, give somewhat higher values than are 

 observed. 



Similar measurements for larger TNT charges (300 gm. equivalent 

 weight) are plotted in Fig. 9.8. Both upper and lower rest positions of 

 maximum peak pressure, corresponding to the vertical lines indicating 

 zero measured migration, are evident, and some similarity is evident in 

 the impulse data. The measured peak pressures at the upper rest 



