Density, blast waves

In the surrounding atmosphere, a blast wave is experienced as a transient change in gas-dynamic-state parameters pressure, density, and particle velocity. Generally, these parameters increase rapidly, then decrease less rapidly to sub-ambient values (i.e., develop a negative phase). Subsequently, parameters slowly return to atmospheric values (Figure 3.7). The shape of a blast wave is highly dependent on the nature of the explosion process. 

An ethylene storage tank in your plant explodes. The distance that the blast wave travels from the blast site (R) depends upon the energy released in the blast (E), the density of the air (p), and time (t). Use dimensional analysis to determine ... 

As a blast wave passes through the air or interacts with and loads a structure or target, rapid variations in pressure, density, temperature and particle velocity occur. The properties of blast waves which are usually defined are related both to the properties which can be easily measured or observed and to properties which can be correlated with blast damage patterns. It is relatively easy to measure shock front arrival times and velocities and entire time histories of overpressures. Measurement of density variations and time histories of particle velocity are more difficult, and few reliable measurements of temperature variations exist. 

Although it is possible to define the potential or kinetic energy in blast waves, it is not customary in air blast technology to report or compute these properties. For underwater explosions, the use of "energy flux density" is more common. This quantity is given approximately by... 

Blast Wave - A transient change in the gas density, pressure, and velocity of the air surrounding an explosion. 

W.A. Anson JM. Dewey, Density Measurements in the Blast Wave from a Surface Burst 500-ton TNT Hemispherical Charge , Suffield Technical Paper No 305, Suffield Experimental Station, Ralston, Alberta, Defense Research Board of Canada (1965) 4) J.R. Osborn, RJ. 

Procedures for Measuring Blast Wave Density in a 500-Ton TNT Surface Burst , Suffield Technical Note No 258, Defense Research Establishment, Suffield, Ralston, Alberta, Canada (1971) 10) W.E.Voreck J.W. McCahill, Scanning Gamma Ray Densitometer System for Detonators , PATR 4239 (1971) 11)WJ. Fenrick... 

Campbell, Canadian Blast Wave Density-Time Measurements on Event DIAL PACK , Defence Res Establishment, Suffield, Ralston, Alberta, Canada (1972) (Limited distrib) 120) A.D. Rooke, Jr et al, DIAL PACK Crater and Ejecta Measurements from a Surface-Tangent Detonation on a Layered Medium , Final Rept, Army Engr Waterways Exptl Sta, Vicksburg... 

The use of beta particle gauging is described for the measurement of blast wave density from the detonation of large charges of high expl on the surface, eg, 500-ton TNT spherical and hemispherical chafes. The basic principle of the gauge is the measurement of the varying absorption of beta particles caused by density changes... 

The density of obstacles can only roughly be distinguished. Planes vertical to the direction of the expansion of the blast wave are considered and the degree of confinement is estimated we use... 

A free-field blast wave emanates from an explosion until it reaches an object and interacts with it. Sources of explosions that have very high energy and power densities produce ideal blast waves that have predictable properties. A blast wave decays with distance from the source. For high explosive materials, the distance for a blast wave is related to the cube root of the charge weight. In some cases, one can estimate the forces involved in an explosion from the fragment distribution pattern. 

The results of a blast wave simulation—that is, pressure-time histories on the solid plate (described previously)—are presented in Fig. 5. Curve 1 (solid line) represents data from a piezogauge mounted in the plate, covered by a 55-im layer of PUR foam with an average density of pQ 25.0 kg/m3. Curve 2 corresponds to the results of one-dimensional numerical simulation using a model of a one-fluid, two-temperature continuum. In order to reproduce initial conditions in our numerical simulations for blast wave/foam interaction, we used density distribution in a nonsteady jet from the shock tube experiment. Other gasdynamical parameters recjuired for the system of Eqs. (2a)-(2c) were derived using the assumption of the Riemann invariant being constant. Curve 3 illustrates pressure gauge data for the same plate without the foam. Mach number of the shock in the end of the tube was about 1.85 in all cases, Pq-I bar. 

However, it is not right to attribute HE blast parameters to those of gas cloud combustion/detonation based only on their energy similarity, such a procedure needs corrections. Let us remind you that the expansion level of gas explosion products is dozens of times less than is recorded for HE explosions. Geometrical dimensions of the low density source of an explosion are large and always comparable with a distance within which the blast wave is dangerous. 

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