Comparison of Head Injuries as Predicted by Three Different Displacement Velocity Models
ENGINEERING ANALYSIS INC HUNTSVILLE AL
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Head injuries cause many of the fatalities produced by blast effects. In such injury predictions, the skull is more vulnerable to dynamic pressure than to overpressure. Dynamic pressure, resulting from the blast wave sweeping over the human body, causes the body to be swept along behind the wave at some displacement velocity. Injuries occur when the moving body encounters stationary, solid structures. The displacement velocities for various skull injury levels are known. Solving the motion equation for a body in a transient flow field yields the displacement velocity as a function of peak overpressure and impulse. Baker, et al. and Mercx previously attempted this computation, but in each case significant deficiencies occurred. In Bakers analysis, both diffraction pressure and drag loading were computed, but the drag on the human body contained no adjustment for the objects motion. Thus, some of Bakers displacement velocities exceeded the particle velocity behind the blast wave, a physically impossibility, resulting in very inaccurate curves at low peak overpressures .4 psi. In Mercxs analysis diffraction pressure loading was neglected, and in calculating the particle velocity behind the blast wave, Mercx used the ambient air density instead of the density behind the wave. These two deficiencies cause considerable inaccuracy at overpressures above 10 psi. In the current Improved Displacement Velocity IDV analysis, the effects of both diffraction pressure-loading and drag-loading were considered, with allowance for the bodys displacement velocity, and with the correct air density used in the particle velocity equation. Pressure-impulse diagrams were calculated based on all three methods for four displacement velocities corresponding to four fracture probabilities. At low pressures the IDV curves closely match Mercxs while lying well above Bakers. Between 3 and 10 psi the IDV curves generally agree with Bakers, as Mercxs drift to the right.
- Anatomy and Physiology
- Weapons Effects (Biological)