SHOCK WAVE MEASUREMENTS 249 



(see section 6.2); for military and practical purposes less symmetrical 

 forms of charge and methods of detonation are therefore almost exclu- 

 sively used, however unfortunate this is from the point of view of sim- 

 plicity in theory and measurement. Other reasons than expediency 

 may also dictate nonspherical shapes of charge, as one may be inter- 

 ested in concentrating explosive effects in one direction at the expense 

 of others. 



A. Line charges. Perhaps the simplest experimentally realizable 

 form of charge which differs considerably from a sphere is a line charge. 



^SHOCK FRONT 



DETONATOR 



\ 



LINE CHARGE 



^;rfvvvvv\v^v\vvvv\vv\vvvvvvv^ -\b 



Fig. 7.12 Shock front around a line charged detonated at one end. 



The line charge is an extremely elongated cylinder which is detonated 

 at one end, the detonation wave progressing the length of the charge 

 with finite velocity and generating a conical shock wave about the 

 cylinder as axis. This situation does not correspond to one-dimensional 

 cylindrical symmetry in which the shock wave is specified by the radius 

 vector from the cylinder axis, but is rather one of axial symmetry in 

 which the coordinate parallel to the axis must also be considered. The 

 extension of the Kirkwood-Bethe theory to cylindrical symmetry by 

 Rice and co-workers, as discussed in section 4.4, does not apply directly 

 to line charges, both because of the finite length of charge and because 

 of the finite detonation velocity. Simpler approximate considerations, 

 however, suffice to explain qualitatively the general differences in pres- 

 sure at different points around the charge. 



In Fig. 7.12, a line charge of length L is detonated from point 0. 

 The detonation wave proceeds with a velocity D toward L, and a shock 

 w^ave forms in the surrounding water. After detonation is complete, 

 the shock will have an outline as indicated, if it is assumed that the 

 cumulative effect of successive elements of the explosive is to be ob- 



