1197 
MEASUREMENTS ON PRESSURE WAVES IN REGION OF TWO OBLIQUELY 
INTERSECTING UNDERWATER SHOCK WAVES 
A. M. Shanes 
Underwater Explosives Research Laboratory 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 
Introduction, When two equal waves intersect, elementary theory 
indicates that the maximum pressure should be apnroximately twice 
that of one of the shocks alone. By more advanced methods, Von 
Neumann (Bureau of Ordnence, Explosives Research Renort No. 12, 1943) 
has shown that when the finite amplitude of the waves is considered, 
the pressure in water should exceed the sum of the components by an 
amount which increases as the waves intersect more and more obliquely, 
1.€., less head-on, At a certain critical angle, however, the 
phenomonon changes qualitatively, the two waves merging into one 
in a certain region (Mach region) about the interseotion plane of 
the two shocks, It has been postulated that in this region the 
pressure at first increases and then falls to a relatively low 
value as the interseation becomes more and more oblique, epproaching 
glancing incidence, 
Experiments on the underwater shock waves from two simultaneous 
explosions have now confirmed this picture, at least qualitatively, 
Pressure-time curves in the region of intersection of the shock waves 
from the two charges were obtained with 4 small piezo gauges, Two 
of the gauges were located on the perpendicular bisector of the 
line joining the charges. The gauge=to-charge distances for these 
gauges were kept constant but the angle of intersection at the gauges 
was varied by changing the charge=to-oharge distance, 
The pressure versus angle curves show the expected maximum 
(Figs. 1, 3, 4). This 18 more pronounced if the observed peak presq~ 
sures are corrected in the customary way for the finite response time 
of the gauges. 
The impulse integral f pat and the energy integral 5c J peat 
were also evaluated (Figs, 5-10), 
From the practical viewpoint these results indicate that a 
given weight of charge should be more effective in oertain direotions 
if divided into two or more) equal parts fired simultaneously. 
For damage tests with double charges see UE-18, p. 68 and UE-19, ¢.21, 
A gauge on the line through the charges showed the expected 
strong shielding of one explosion by the gas bubble of the other. 
Method, The shock waves studied were generated by the a imultsaneous 
detonation of the two oa, 1700 g. spherical cast pentolite charges 
and recorded by 0,22" diameter doublet piezo gauges. The arrange- 
ment of charges (C) and gauges (G-A, GB, G-2, G4, GZ) is shown 
in the following sketoh, 
