Modeling Environment

The analysis of the consequences of nuclear accidents began with physical concepts of core melt, discussed the mathematical and code models of radionuclide release and transport within the plant to its release into the environment, models for atmospheric transport and the calculation of health effects in humans. After the probabilities and consequences of the accidents have been determined, they must be assembled and the results studied and presented to convey the meanings. [Pg.331]

Mehta, R.V. and Tarbell, J.M., 1983. A four environment model of mixing and chemical reaction. Part I - model development. American Institution of Chemical Engineers Journal, 29, 320. [Pg.315]

Many mixing models which utilize the simplified concepts of micro-mixing and segregation have been introduced. Most notable of these are the two-environment models of Chen and Fan (19), Kearns and Manning (20), and others (21, 22), and the dispersion models of Spielman and Levenspiel (23), and Kattan and Adler (24). [Pg.297]

Rizzoli AE, Young WY (1997) Delivering environmental decision support systems software tools and techniques. Environ Modell Softw 12(2-3) 237-249... [Pg.144]

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Schliiter M, Savitsky AG, McKinney DC, Lieth H (2005) Optimizing long-term water allocation in the Amudarya River delta a water management model for ecological impact assessment. Environ Modell Softw 20 529-545... [Pg.144]

Newham LTH, Letcher RA, Jakeman AJ, Kobayashi T (2004) A framework for integrated hydrologic, sediment and nutrient export modelling for catchment-scale management. Environ Modell Softw 19(11) 1029-1038... [Pg.145]

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Export processes are often more complicated than the expression given in Equation 7, for many chemicals can escape across the air/water interface (volatilize) or, in rapidly depositing environments, be buried for indeterminate periods in deep sediment beds. Still, the majority of environmental models are simply variations on the mass-balance theme expressed by Equation 7. Some codes solve Equation 7 directly for relatively large control volumes, that is, they operate on "compartment" or "box" models of the environment. Models of aquatic systems can also be phrased in terms of continuous space, as opposed to the "compartment" approach of discrete spatial zones. In this case, the partial differential equations (which arise, for example, by taking the limit of Equation 7 as the control volume goes to zero) can be solved by finite difference or finite element numerical integration techniques. [Pg.34]

Montzka C, Canty M, Rreins P, Kunkel R, Menz G, Vereecken H, Wendland F (2008) Multispectral remotely sensed data in modelling the annual variability of nitrate concentrations in the leachate. Environ Modell Softw 23(8) 1070-1081... [Pg.46]

Trevisan M, Di Guardo A, Balderacchi M (2009) An environmental indicator to drive sustainable pest management practices. Environ Model Software 24(8) 994-1002... [Pg.68]

Stewart RN, Purucker ST (2011) An environmental decision support system for spatial assessment and selective remediation. Environ Model Softw 26 751-760... [Pg.107]

Fig. 9. Calculated structures of the precursor complex within different environment models (159).

The basis idea behind multi-environment models is that the mixture fraction at any location in the reactor can be approximated by a distribution function in the form of a sum of delta functions as follows ... [Pg.248]

The simplest model of this type is the two-environment model (N — 2) for which the independent state variables in the CFD model are... [Pg.249]

In theory, this model can be used to fix up to three moments of the mixture fraction (e.g., (c), ( 2), and (c3)). In practice, we want to choose the CFD transport equations such that the moments computed from Eqs. (34) and (35) are exactly the same as those found by solving Eqs. (28) and (29). An elegant mathematical procedure for forcing the moments to agree is the direct quadrature method of moments (DQMOM), and is described in detail in Fox (2003). For the two-environment model, the transport equations are... [Pg.249]

Although we will not do so here, with a little more work one can use Eqs. (36)—(38) to find the transport equation for ( 3). The two-environment model thus provides an extra piece of information that can be compared to experimental data. [Pg.249]

The next step would be to implement the CFD transport equation for the state variables in a CFD code. This is a little more difficult for the two-environment model (due to the gradient terms on the right-hand sides of Eqs. 37 and 38) than for the moment closure. Nevertheless, if done correctly both models will... [Pg.249]

The multi-environment model for the joint PDF generalizes Eq. (33) by writing... [Pg.261]

The reader will recognize these terms as having of the same form as the correction terms in the two-environment model discussed earlier. With N — 1, 6 j = 0 and the model reduces to the laminar-chemistry approximation. With N —2, additional information is obtained concerning the second-order moments of the composition vector. Likewise, by using a larger N, the Mh-order moments are controlled by the DQMOM correction terms found from Eq. (89). [Pg.270]

In practice, it may be difficult to determine in advance which method is best to use for a particular application. For example, the CFD results may be more sensitive to large-scale inhomogeneities in the flow field than to the chemical source term closure. A rational approach to determine whether a more detailed SGS model is needed might be to start with N — 1 (laminar-chemistry approximation) and compare the predicted mean chemical species fields to the two-environment model (N — 2). If the differences are small, then the simpler model is adequate. However, if the differences are large, then the CFD simulation can be repeated with N — 3 and the results compared to N — 2. Naturally, once this procedure has converged, it will still be necessary to validate the CFD results with experimental data whenever possible. Indeed, it may be necessary to... [Pg.272]

The multi-environment model for turbulent transport of the bi-variate moments in the absence of moment source terms has the form... [Pg.284]

Note that the correction terms are proportional to fT and result from turbulent velocity fluctuations (represented by a gradient-diffusion model). For the multi-environment model the composition vector is defined by... [Pg.285]

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