CHRISTIAN: THE ACOUSTIC OUTPUT OF EXPLOSIVE CHARGES 



theoretical treatment that takes as input an explosive charge 

 composition, weight, and depth and gives in return realistic, reli- 

 able pressure-time histories at any desired range. This problem has 

 been worked on for many years, and we are coming closer than Kirkwood 

 and Bethe might have hoped for. But we are still in an empirical 

 world when trying to examine source levels parametrically . 



Let me show you a sample of data that illustrates the kinds of 

 wave-form changes we have to deal with. In Figure 5 some recorded 

 pressure waves are sketched on the right, and the experimental 

 arrangements used to record them is shown on the left. We lowered 

 a small oscilloscope housed in a 30-inch diameter sphere down to 

 about 14,000 feet. A tourmaline gage was suspended below the sphere, 

 and 50-pound pentolite spheres were suspended some 200 to 1,000 feet 

 below the gage. We also had pressure sensors near the surface above 

 the charges. 



In the pressure waves shown on the right of Figure 5, solid 

 lines represent the data measured with the deep oscilloscope near 

 the charge, and dashed lines represent the same pressure wave 

 measured near the surface. The upper pair of curves are for a charge 

 fired 3 90 feet below the deep gage; the lower pair are for a charge 

 935 feet below the gage. In both cases, the pressure waves for the 

 deep (near-field) and shallow (far-field) recordings are plotted on 

 scales in the same ratio as the stand-off ranges. In other words, 

 had the waves propagated without changes of shape — simply decreased 

 in amplitude at the acoustic rate of 1/R — the solid and dashed 

 curves would coincide. The top set of curves, where measurements are 

 compared for ranges of 190 and 13,690 feet, shows the well known 

 shock-wave "finite amplitude effects" of a spreading profile and a 

 peak pressure that decays more rapidly than 1/R; it also shows that 

 the same nonlinear behavior is followed in the first bubble pulse. 



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