FEM3C, An improved three-dimensional heavy-gas dispersion model: User`s manual

Abstract

FEM3C is another upgraded version of FEM3 (a three-dimensional Finite Element Model), which was developed primarily for simulating the atmospheric dispersion of heavier-than-air gas (or heavy gas) releases, based on solving the fully three-dimensional, time-dependent conservation equations of mass, momentum, energy, and species of an inert gas or a pollutant in the form of vapor/droplets. A generalized anelastic approximation, together with the ideal gas law for the density of the gas/air mixture, is invoked to preclude sound waves and allow large density variations in both space and time. Thee numerical algorithm utilizes a modified Galerkin finite element method to discretize spatially the time-dependent conservation equations of mass, momentum, energy, and species. A consistent pressure Poisson equation is formed and solved separately from the time-dependent equations, which are sequentially solved and integrated in time via a modified forward Euler method. The model can handle instantaneous source, finite-duration, and continuous releases. Also, it is capable of treating terrain and obstructions. Besides a K-theory model using similarity functions, an advanced turbulence model based on solving the k - {var_epsilon} transport equations is available as well. Imbedded in the code are also options for solving the Boussinesq equations. In this report, an overview of the model is given, user`s guides for using the model are provided, and example problems are presented to illustrate the usage of the model.