935 
NOTE ON THE WATER FORMATION PRODUCED BY AN 
UNDERWATER EXPLOSION ON THE MODEL SCALE 
A. J. Harris 
Road Research Laboratory, 
London 
August 1943 
* * * * * * * * 
Summary. 
Spark photographs nave been taken of tne vertical movement of water produced by the 
explosion of a No.8 cetonatcr at 1 inch below the water surface in a model tank. 
Analysis of a drum camera "sChlieren* recora shows that the shock wave leaves the water 
surface with a velocity some 50 oer cent greater than that of sound. 
In order to throw light on the experimental results the transmission of shock waves 
through a water-air interface has been examined theoretically. Tne intensity of the shock wave 
in water has been evaluates from the velocity measurements and the effect of oblique Incidence 
has been studied. 
ae 
I. EXPERIMENTAL 
Introduction. 
Previous reports have veen given of the "dome" ana "plume" formation produced by the 
explosion of a No. 8 detonator in water, studied by means of a succession of onotographs taken 
at 1# milliseconds intervals, The initial vertical velocity of the water formation has been 
measured with a rotating Orum camera, a “schlieren™ technique being used to show that the shock 
wave leaves the water sutface at tne instant at which it begins to move upwares, This present 
report deals in more cetail with the movement of water and the accomoanying shack wave from the 
explosion of a detcnatot 1 inch deep. 
Experimental methods: Spark photography. 
with a detonator 1 inch dees the initial movement of the water surface is about 
1,000 ft./second - too rapid for tne emoloyment of the orevious photographic method having a 
oleture frequency of only 700 cictures/second., A number cf spark photograohs of the phenomena, 
i.e. movement of water surface and accomoanying shock wave, were tnerefore obtained at intervals 
of about 100 microseconds corresponding to a picture frequency of about 10,000 sictures second. 
The excerimental arrangement employed is shown in Figure 1 being tnat originally aevisea by 
Cranz and Scnardin. Soark 1 1s triggered through a thyratron by a diaonragm contact in the 
water near the detonator and the succeeding soarks are triggered In succession by suitable 
electric delay circuits. Spark 1 orovides the i}lumination for the record given by camera 1 ana 
soon; in this way up to nine shadow olctures can be obtained at intervals ranging from 2 to 
200 microseconds deoending on the characteristics of the delay circults, 
Drum camera record. 
The drum camera record of the water front and of the shock wave front was obtained by 
the "schileren® method described oreviously. 
Results obtgined. 
A selection of the soark phctographs ootainea are given in Figures 2and 3. Figure 2 
Shows successive stages in the water formation ana Figure 3 shows a later stage more clearly. 
WATOT cones 
