Adjoint method for assessment and reduction of chemical risk in open spaces
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Chemical accidents and chemical terrorisms are threats to people's health and lives. To predict and assess the potential risk of chemical leakage is of great importance for decision-makers to reduce risk and panic beforehand. When the chemical gas releases into an open space, the transfer and diffusion of the poisonous aerosol is directly affected by meteorological factors, so the atmospheric dispersion model incorporated with meteorological information should be applied in the assessment. There are two approaches to calculate the risk value. One is the direct approach, which applies the atmospheric dispersion model to compute the concentration of poisonous gas and then, the risk value. However, the location where the accident takes place is often unknown beforehand, so the direct approach means that one must run the model repeatedly for every possible location of sources. An alternative approach ??? the adjoint method is developed in this paper. It is shown that with the adjoint method, the formulation of the risk value can be transformed equivalently. With the new formulation, by solving the adjoint problem, time and computer expense can be considerably saved. Both continued and discrete adjoint formulations are presented. Numerical simulations are carried on to illustrate the adjoint method. The method developed in this study is a good tool to support decision-makers to locate chemical factories or storages, to design optimal paths for transporting dangerous materials, and to assign guard forces for chemical incidents.
Keywordschemical accident chemical terrorism risk assessment adjoint method numerical model
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