Use of point source models for the dispersion of releases of finite size推荐.pdf

Journal of Hazardous Materials 59 1998 235–250 Use of point source models for the dispersion of releases of finite size P.L. Thibaut Brian, Gene K. Lee Air Products and Chemicals, 7201 Hamilton Bl d., Allentown, PA 18195, USA Received 28 February 1997; received in revised form 31 October 1997; accepted 1 November 1997 Abstract If the releases are of finite size, the point source model is widely accepted as an approximation to the concentration in the far field. However, substantial improvement upon the point source model can be achieved by shifting the origin of the point source release to a virtual origin, a point upwind of the origin of the finite size release. In this paper, rigorous solutions for the finite size release models are compared against the point source model to determine the optimum virtual origin shift so as to produce the most accurate approximation in the intermediate and far fields. Also, the effects of anisotropic diffusion are considered in order to model atmospheric diffusion more closely. 1998 Elsevier Science B.V. Keywords: Point source model; Virtual origin; Virtual source; Anisotropic diffusion; Atmospheric dispersion; Finite size release 1. Introduction Point source models are widely used to assess the consequences of releases of toxic and flammable materials to the atmosphere. If the releases are of finite size, it is understood that the point source model is not a good approximation to the concentration in the near field, but it is widely accepted as an approximation to the concentration in the far field. In many situations there is interest in accurately modeling the concentration in the intermediate field. These include situations in which a ‘top hat’ model, including initial momentum or buoyancy, is to be blended into an atmospher