695 



SURFACE WAVES PRODUCED BY FIRING UNDERWATER 32-lb. 

 CHARGES OF POLAR AMMON GELIGNITE AT VARIOUS DEPTHS 



G. Charlesworth 



Road Research Laboratory, 

 London 



February 1945 



Suv 



The amplitiKies of the surface waves oroauced By firing underwater 32-lD. charges of P.A.G. 

 at various asoths in about 15 feet of water have Deen measured Dhotograohical ly. The waves were 

 photograohed by means of a 15-mm. cine camera as they passed along a reference board located in 

 the surface ».t a horizontal distance of 55 feet from the charge. 



In all but one case, the second wave had the largest oositive amolitude and the largest 

 negative amol i tude was eqial to or greater than this. The oeriodicity of the waves was not very 

 different for all charge depths, the period in the region of the first and second waves being 

 about 2.5 to 3 seconds. The velocity of the waves was estimated at about 8 feet/secona ana the 

 wavelength about 20 to 25 feet. 



Largest positive amolitu3es were obtained for charge depths in the region of 0.6 times 

 the maximum bubble radius. Comparison of the results with those obtained from 2-oz. and 2-lb, 

 charges of !=.A,G. showed that the jositive amplitudes did not scale up as much as expected on a 

 one-fourth power law, sugjcsting acssibly a loss of wave making efficiency as the charge weight 

 was increased from 2 cz. tc 32 lo. The 32-lc. charge results, however, agreed quite well with 

 those from 30O-IC. T.N.T. oeoth charges. This m;y mean that fcr fairly large charges, there 

 is little Change in efficiency as the scale :f the mciel is incrjase3. 



Intfoducti on . 



The object of the tests was tc obtain further experimental data on scale relationships 

 involved in wave making by means of explosives^ 



Exi>erimental . 



Charges. 



The Charges were of °olar Ammon gelignite, 32 lb, in weight, and were initiated by 4 oz. 



of C.l. 



Measurement of wave amplitude. 



Amclituoes were measured by chotogr.-'.ohing the waves as they passed along a reference 

 board set in the water surface. The boanJ was of tinclatc 6 feet long x about 3 feet high. 

 The camera used wiS a 16-mm. cine- earner?, with a lens of focal length 3 inches and the camera 

 was run at about 16 frames/second. 



Site and arrangement cf tests . 



The tests were made in a grave) pit in acout 15 feet of water. The centre of the 

 reference board was placed at a norizcntal distance of 55 feet from the charge. The camera was 

 located on the bank at a distance of about 'C feet from the Doaro, A pHn view of the layout 

 of the tests is shown in Figure 1. 



LXPerimental 



