Blast Waves by Charles E. Needham

Author:Charles E. Needham
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

The vast difference in the behavior of the radiated energy has a marked effect on the formation and propagation of the blast wave which is not accounted for by the modified Sachs scaling rules . For small to moderate changes in the altitude of burst, (perhaps less than a few kilometers) and for small variations in yield (one order of magnitude), the scaling relations provide a good approximation to the behavior at intermediate (30 bars to 0.1 bars) pressure levels.

I will make one more observation about nuclear blast wave s. When comparisons are made between the scaled pressure vs. range curves from the Nevada Test Site (NTS) and the Pacific Proving Ground (PPG) tests a systematic difference is found between the two sets of data. Figure 12.5 illustrates the differences for pressures below one bar. The pressure vs. range curve for the PPG tests falls well below the NTS data with only a few exceptions. Closer examination of the comparisons shows the majority of the PPG tests being compared were for yields of half a megaton or more, whereas the yields of the NTS test were all less than about 70 KT. The lower yield PPG tests show good agreement with the NTS test data. Numerical calculations of the large yield PPG tests show that the radius of the shock at intermediate level pressures (30 bars to 0.1 bars) is the order of or greater than the scale height of the atmosphere. This means that the changing pressure of the atmosphere in the upward moving shock can be communicated to the horizontally propagating shock and energy is diverted to the vertical direction. The pressure therefore decays more rapidly in the horizontal direction for megaton yields than for kiloton yields. Nearly all pressure measurements in the Pacific were taken at ground level or within 3 km above the ground. The 3 km altitude data falls along the same line as the sea level measurements when scaled back to sea level. The pressure scale height, the distance over which the pressure falls by a factor of e, the base of the natural logarithms (2.72), is the order of 8 km.

Fig. 12.5Low overpressure comparisons of Nevada and Pacific test data

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