Blast wave modification by detonator placement
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ORIGINAL ARTICLE
Blast wave modification by detonator placement C. Needham1 · J. Brisby2 · D. Ortley2 Received: 19 May 2019 / Revised: 26 March 2020 / Accepted: 24 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The blast wave generated by a high explosive detonation is dependent not only on the shape of the charge but on the location of the detonator or detonators. Even for a spherical charge, the blast wave can be very asymmetric if the initiation is not at the center of the charge. The asymmetry is even greater for cylindrical charges. High-resolution, high-fidelity calculations of the blast wave generated by several spherical and cylindrical charges have been used to quantify these differences for free-field blast propagation. Except for the center-detonated spherical charge, the blast wave never becomes spherical. Several examples are shown to demonstrate and quantify the asymmetries and to illustrate that the blast wave, once asymmetric, can never regain spherical symmetry. At distances of over 40 charge radii, the asymmetries are clearly defined. As the overpressure at the shock front decays below half a bar, the propagation velocity approaches ambient sound speed. At half a bar (50 kPa), the Mach number of the shock is 1.19 and at a tenth of a bar (10 kPa) the shock velocity is only Mach 1.04. If the shock front is asymmetric at low overpressures, all parts of the shock front are moving at very nearly the same velocity and can therefore never “catch up” to other parts of the front: once asymmetric, always asymmetric. Results of several calculations have been analyzed to determine the quantitative differences in shock properties resulting from detonator placement and charge shape. Properties are significantly different behind the shock fronts, especially in the density distribution. Keywords Blast wave · Detonation · Spherical and cylindrical charges · Hydrodynamic calculation
1 Background Within the period of a few weeks, we reviewed two articles in which the authors used the blast wave produced by a spherical charge to compare with experimental blast data from cylindrical charges. It is apparently widely held that the blast wave from a cylindrical charge is indistinguishable from that of a spherical charge of the same mass at distances greater than “a few charge radii.” Allen Ohrt performed experiments in which a Comp-B cylinder with a length-todiameter ratio of 5 was detonated at the top axial position. Figure 1 shows the comparison of the equivalent spherical charge weight as a function of radius along different radials based on experimental overpressure data [1]. This demonstrates the effective yield relative to a spherical charge. At Communicated by O. Igra. * C. Needham [email protected] 1
Needham Consulting LLC, Albuquerque, NM, USA
Applied Research Associates, Southwest Division, Albuquerque, NM, USA
2
a scaled distance of 1 m, in the equatorial plane, the overpressure is equivalent to that of more than a 6-kg spherical charge. Note that at 45 degrees
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