EXCESS PRESSURE 4p (LA/IN') 
1 
REDUCED TIME 
Fic. 11. Composite pressure-time curves for first and 
500 ft.; distance from center of charge: R= W1/0.352. ( 
© 0.5-lb. charges. X 2.5-lb. charges. @ 12.0-lb. charges. 
it is found, using the curve of Fig. 11; that the 
net flow is 9.7 cu. ft. per lb. toward the bubble. 
The ratio of the volume of the bubble at its 
second maximum to its volume at first maximum 
should therefore be 
(17.0—9.7/17.0) =0.43, 
since the volume of 17.0 cu. ft. was found in 
Section 19 to be the total outward flow up to 
the time t=fy1. 
As in Section 19, we have at our disposal an 
equation giving the second bubble maximum in 
terms of the charge size and the depth: 
Ay2=J2(W/Zo)', 
where J2=8.5. 
The ratio of the first and second maximum 
volumes as obtained from direct bubble radius 
measurement is, therefore, 
(A m2/A m1)? = (J2/J1)? =0.31. 
This ratio is considerably lower than the value 
of 0.43 given above by Eq. (35), but the dis- 
crepancy is in the direction of the samme type of 
base line error that probably caused the net 
impulse to be positive. In this case the effect 
would be somewhat exaggerated because of the 
(42) 
17W9 — (MSEG/LBh) 
second bubble pulses. Explosive: TNT; charge depth: 
Based on measurements cited in reference 2.) Legend: 
cumulative effect of base line error upon the 
integration. 
The impulse of the second bubble pulse will 
not be considered as the error in the base line 
in that region is excessive. 
‘ 
22 
The radiated energy flux for the first bubble 
pulse is given by the equation 
tM» 
re 
Co Yim, 
Polo 
Fri= (43) 
(Ap) dt. 
Integration of the energy flux from the com- 
posite of Fig. 11, yields 
Fri/W'=139(in.-lb./in.? lb.4) (at R= W4/0.352) 
and 
Epri/W =121(cal./g). 
Similarly, for the second bubble pulse 
Fr2/W3=16.8(in.-lb./in.? lb.}) 
(at R= W?/0.352), 
Ep2/W=14.7(cal./g). 
The error in the energy flux of bubble pulses 
caused by error in the base line is very small 
