260 SHOCK WAVE MEASUREMENTS 



changes in duration are not predicted by existing theory, which assumes 

 shock fronts of infinite duration, but an upper hmit on what can be ex- 

 pected must obviously be set by the fact that the total energy of the 

 two shock waves is only double that for a single one. 



The experimental results so far obtained do not indicate tremendous 

 increases in effectiveness of shock waves by their nonlinear combination, 

 but the various possibilities have hardly been explored in any detail, 

 and the subject merits further investigation. 



DETONAT 



Fig. 7.20 Mach reflection scheme for a cylindrical charge. 



The phenomenon of multiple shock fronts off the ends of cylindrical 

 charges, particularly off the end near which detonation is started, must 

 be the result of interactions of shock fronts, and a possible explanation 

 of the effect may be similar to one suggested by G. T. Reynolds (91) for 

 the case of air blast waves which exhibit similar properties. 



The initiation by the detonator near one end of a cylindrical charge 

 sets up a detonation wave, which on reaching the surfaces of the charge 

 develops shock fronts in the water off the end and off the sides of the 

 charge, as indicated schematically in Fig. 7.20. At points such as F, 

 however, the intersection of two shock fronts at different pressures con- 

 stitutes a physically impossible situation, which must result in a new 

 shock front. A front O'Y behind OY, if this is weaker than the front 

 YB, can provide the necessary continuity of pressure in the region be- 

 hind O'YB. 



The fronts sketched in Fig. 7.20 are similar to the Mach F, the front 

 OY corresponding to an incident wave, O'Y to its reflection and YB to 



