Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Discrete ordinates model

Probability Density Function model (PDF) Discrete Ordinate model (DO) Euler-Lagrangian model... [Pg.19]

The simulation should be carried out in a step-by-step procedure developing from a lower to a higher level of complexity. For example, radiation was taken into account in the late stages of the calculation starting from PI to discrete ordinates model. Initially, the numerical calculations are made on a stationary time scale. If the convergence of the overall case shows a periodical behavior, the stationary solution can be used to initialize the transient calculation as in the case of INCI simulation. [Pg.148]

The 1-D discrete ordinates model (XSDRNPM), used for the power density profile calculation shown in Fig. 5.1, was used to calculate the dose rate at the outside surface of the graphite reflector. The calculation was performed with the SCALE 27 neutron-18 gamma group library (ENDF/B-V). The dose rates were calculated at the axial midplane and 1 cm above the outside surface of the reflector. The neutron dose rate, as calculated with the American National Standards Institute (ANSI) standard flux-to-dose-rate factors, was 5200 rem/h, and the gamma dose rate (ANSI standard) was 250 rem/h. The gamma dose rate should be regarded as a minimum estimate. Software and data library developers are uncertain as to whether the prompt fission gammas were accurately represented in the calculation. [Pg.91]

Long term observations indicate that UV-B radiation reaching the earth s surface may have decreased by 5-18% since the industrial revolution in the industrialised midlatitudes of the Northern Hemisphere (NH). However, on a global basis, this may have been offset by the stratospheric ozone layer reduction. It is not possible to estimate the net effect from both, attenuation and increase, because of the limited amount of spatial and temporal coverage of measurements (Liu et al., 1991). In an attempt to present calculated and modelled effects of aerosol on UV flux the authors used the Discrete Ordinate Radiative Transfer Model (DISORT Stammes et al. 1988) for different visual ranges and boundary layer depths (Figure 1). The decrease at 310 nm is 18% and 12 % for a 2km and 1km PBL respectively. [Pg.144]

In the case of high liquid water clouds, the D(X) value can be as high as 10 as noted by Madronich [109,110] and co-workers. For example, they note that measurements of spectral ultraviolet-B irradiance under optically thick clouds show strongly enhanced attenuation by molecular and particulate absorbers and that the photon path is enhanced due to the presence of the highly scattering medium, leading to an amplification of absorption by chromophores. Using discrete ordinate and Monte Carlo model caculations, they [110] showed that photon paths (i.e., D(X)) in realistic water clouds could be enhanced by factors of 10 and more compared to cloudless sky. ... [Pg.101]

The discrete ordinates (DO) approximation is also a multiflux model. The discrete ordinates approximation was originally suggested by Chandrasekhar [19] for astrophysical applications, and a detailed derivation of the related equations was discussed by several researchers for application to neutron transport problems [33, 57-61], During the last two decades the method has been applied to various heat transfer problems [62-81]. [Pg.554]

S2 and S4 Models for Cylindrical Geometries. For the solution of the RTE in cylindrical media, the formulations for the S2 and S4 discrete ordinates (DO) approximations (based on Ref. 69) will be presented here. Note that, in a more recent study, Jendoubi et al. [75] used a similar DO approximation in cylindrical geometry and evaluated the effect of anisotropic phase function on the accuracy of the model. [Pg.555]

V11.15. Computational methods that directly solve forms of the Boltzmann transport equation to obtain k j are preferred for use in the criticality safety analysis. The deterministic discrete ordinates technique and the Monte Carlo statistical technique are the typical solution formulations used by most criticality analysis codes. Monte Carlo analyses are prevalent because these codes can better model the geometry detail needed for most criticality safety analyses. Well documented and weU validated computational methods may require less description than a limited-use and/or unique... [Pg.350]

An alternative to the above modeling approach is to simulate thermal radiation exchange using a conservative variant of the discrete ordinates (DO) radiation model, called the finite-volume (FV) scheme, implemented in the Fluent software package. [Pg.291]

To describe the heat transfer by radiation, FLUENT provides the following radiation models Rosseland model, PI model, discrete transfer radiation model (DTRM), surface to surface model, and discrete ordinates (DOs) model [32, 36]. These are explained in more detail in [38]. Due to its suitability for the entire range of optical density and the justifiable cost of computation, the DOs model is used to model the reactors used to process fuel. In contrast to other radiation models, the DOs model does not track individual heat rays but solves the radiative transfer equation (RTE) in the discrete directions. [Pg.717]

Because of the limitations inherent in representing a real sample as a continuum, the more sophisticated radiative transfer models, such as the discrete ordinate approximation or the diffusion approximation, hold little hope for obtaining for a better understanding of the effects occurring in diffuse reflection spectrometry for the general case. [Pg.62]

Discrete Ord inates Model The discrete ordinates method is capable of resolving the nonisotropic directional characteristics of radiative heat transfer by subdividing the directional space into discrete solid angles. After preselecting a set of representative discrete directions the radiative-transfer equations as well as the corresponding boundary conditions can be written as a set of equations for each direction, which is then solved. However, the equations for each direction depend on each other if scattering and reflection is considered. [Pg.150]

The co-ordinated Kaapvaal Project geochron-ological studies of crustal and mantle xenoliths reveal that both crust and mantle have experienced a multi-stage history, and that a simple view of cratonization as a discrete event is not a viable model for craton formation (Schmitz et al. 1998 Schmitz Bowring 2000 Moser et al. 2001). The lower crust in particular retains a comprehensive record of the tectonothermal evolution of the lithosphere. The study of lower-crustal samples has shown that much of the deep craton experienced a dynamic and protracted history of tectonothermal activity that is temporally associated with events seen in the surface record, including late Archaean magmatism (Ventersdorp) and even Proterozoic deformation (Namaqua-Natal) (Schmitz et al. 1998). Thermal events are... [Pg.6]

The discrete formulation is based on the modelling of the nodes (both demand and supply) in the network as horizontal lines in a two dimensional discrete space. The position of each line is represented by (x,y). The y value specifies the head at the node. The length of a horizontal line in this discrete space represents the amount of water through the node, irrespective of the actual location along the x-axis. Transportation of water from one node to another occurs when the lines corresponding to the two nodes overlap (in terms of the x co-ordinates) provided a connection between the two nodes is allowed. The definition of the network is actually a superstructure of allowable pipe connections, pipe diameters and distances between nodes. [Pg.120]


See other pages where Discrete ordinates model is mentioned: [Pg.649]    [Pg.649]    [Pg.158]    [Pg.171]    [Pg.172]    [Pg.131]    [Pg.560]    [Pg.185]    [Pg.198]    [Pg.340]    [Pg.789]    [Pg.584]    [Pg.184]    [Pg.563]    [Pg.567]    [Pg.351]    [Pg.199]    [Pg.204]    [Pg.120]    [Pg.408]    [Pg.477]    [Pg.239]    [Pg.240]    [Pg.240]    [Pg.131]    [Pg.22]    [Pg.50]    [Pg.6]    [Pg.43]    [Pg.1]    [Pg.49]    [Pg.22]    [Pg.929]    [Pg.354]    [Pg.104]   
See also in sourсe #XX -- [ Pg.150 ]




SEARCH



Discrete models

Model Ordinance

Ordinal

© 2024 chempedia.info