Shock front interactions
DM&A study shock-on-shock interactions and shock
reflections from the ground and rigid structures. Shock front trajectory analysis is used
to calculate values of peak physical properties such as hydrostatic overpressure
immediately behind the shock fronts. These data complement those measured by smoke
tracers and electronic pressure transducers.
The primary shocks from two identical, separated explosive charges meet to form
a complex reflection seen as a vertical refractive image between the two arrows, against a
prepared background of striped canvas sails about 50 feet high. The primary shock from the
lower charge occupies the centre third of this refractive image and the Mach stem from its
reflection at the ground, the bottom third. Its triple point is nearly level with the
lowest pressure gauge on the left hand striped pole. Another Mach stem occupies the top
third of the image, created when the lower primary shock was reflected from that of the
upper charge. Its triple point is seen just below the third-lowest pressure gauge. Because
the two charges were identical, detonated simultaneously and separated by a distance equal
to twice the height of the lower charge, the two Mach stems can be compared and observed
differences in speed, strength, shape, etc., attributed to the nature of the ground
surface. Above, the Mach stem at the ground surface lags slightly behind the Mach stem
above it, because the ground surface absorbs some of its energy.
DM&A have analyzed more complex interactions than that shown above,
including non-simultaneous multiburst events.