Concentration fluctuations in gas releases by industrial accidents

M. Nielsen, P.C. Chatwin, Hans Ejsing Jørgensen, N. Mole, R.J. Munro, Søren Ott

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    Abstract

    The COFIN project studied existing remote-sensing Lidar data on concentration fluctuations in atmospheric dispersion from continuous sources at ground level. Fluctuations are described by stochastic models developed by a combination of statisticalanalyses and surface-layer scaling. The statistical moments and probability density distribution of the fluctuations are most accurately determined in a frame of reference following the instantaneous plume centreline. The spatial distribution of thesemoments is universal with a gaussian core and exponential tails. The instantaneous plume width is fluctuating with a log-normal distribution. The position of the instantaneous plume centreline is modelled by a normal distribution and a Langevin equation,by which the meander effect on the time-averaged plume width is predicted. Fixed-frame statistics are modelled by convolution of moving-frame statistics and the probability distribution for the plume centreline. The distance-neighbour function generalizedfor higher-order statistics has a universal exponential shape. Simulation tools for concentration fluctuations have been developed for either multiple correlated time series or multi-dimensional fields. These tools are based on Karhunen- Lo`eve expansionand Fourier transformations using iterative or correlation-distortion techniques. The input to the simulation is the probability distribution of the individual processes, assumed stationary, and the cross-correlations of all signal combinations. The usein practical risk assessment is illustrated by implementation of a typical heavy-gas dispersion model, enhanced for prediction and simulation of concentration fluctuations.
    Original languageEnglish
    Number of pages140
    ISBN (Print)87-550-3026-2
    Publication statusPublished - 2002
    SeriesDenmark. Forskningscenter Risoe. Risoe-R
    Number1329(EN)
    ISSN0106-2840

    Keywords

    • Risø-R-1329
    • Risø-R-1329(EN)

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