Simulation of the Effects of an Air Blast Wave - ELSA - Europa

pressure p min . The duration of the negative phase is denoted as t n .- The incident overpressure impulse, which is the integral of the overpressure curve over thepositive phase t d .The idealised (free air blast) form of the pressure wave of Figure 1 can be greatly altered by themorphology of the medium encountered along its propagation. For instance, peak pressure can beincreased up to 8 times if the wave is reflected on a rigid obstacle. The effects of the reflectiondepend on the geometry, the size and the angle of incidence. By setting γ = 1.4 (ratio of specificheats of air), it can be shown that the reflected overpressure p r ispr2 p⎡7p+ 4p0 max=max ⎢ ⎥7 p0 + pmax⎣⎤⎦(2)All parameters of the pressure time curve are normally written in terms of a scaled distanceZ = d3W(3)where W is the mass of the explosive charge and d the distance to the centre of the charge.2.2 Literature Data2.2.1 Pressure-Time DistributionThere are available in the literature several pressure-time-curves for different kinds of explosions.The effects of nuclear explosions here should be disregarded.The pressure at a known point can be described by the modified Friedlander equation (from Baker[2]) and depends on the time t from the arrival of the pressure wave at this point ( t = t0−t a)⎛ t ⎞pt () = p0 + pmax⎜1−⎟⎝ td⎠bt−td(4)The other parameters involved are the atmospheric pressure p 0 , the maximum overpressure p max andthe duration of the positive pressure t d . The parameter b describes the decay of the curve. It can becalculated with a known minimum pressure after the positive phase. Alternatively, the parameter bcan be calculated with the knowledge of the impulse. This will be done in chapter 2.2.5.All parameters for the pressure-time curve can be taken from different diagrams and equations(Baker [2], Kinney [15], Kingery [14], see e.g. Figure 2).8