Instantaneous Release

The concentration profile c = c(x,y, Z,t) for instantaneous release (Fig. E.2) is given in Eq.E-9, with exponential decay in x,y, Z described by means of ('passive') dispersion coefficients ox = Oy, Oz, and with near field top-hat profile (e.g. sharp-edge jet) developing into a Gaussian profile in the far field.

Fig. E.2 UDM geometry for instantaneous release [203]

where

p 32 42a xa ya

z

n

42a z

y y42S y 0

The co-ordinate Z indicates the vertical distance above the Plume centre-line and perpendicular to the y-direction. The angle between the plume centreline and the horizontal is denoted by 0, and the vertical plume height above the ground by zcid. Thus z and Z are related to each other by z = Zcld + Z. Furthermore, Xcld(t) is the downwind distance of the centre of the cloud at time t, and Q; is the mass (kg) in the initial instantaneous at time t. At the core averaging time the along wind dispersion is assumed to be identical to the cross-wind dispersion, i.e. 42a x = Rx = Ry. When m = n = 2, Equations (Eq. E-9) reduce to the Gaussian form.

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