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in creator/contributor: "Morel, J. E."

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Discrete-ordinates electron transport calculations using standard neutron transport codes. [1. 0 MeV]

The primary purpose of this work was to develop a method for using standard neutron transport codes to perform electron transport calculations. The method is to develop approximate electron cross sections which are sufficiently well-behaved to be treated with standard S/sub n/ methods, but which nonetheless yield flux solutions which are very similar to the exact solutions. The main advantage of this approach is that, once the approximate cross sections are constructed, their multigroup Legendr… more

Date: January 1, 1979

Creator: Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Investigation of linear-discontinuous angular differencing for the 1-D spherical-geometry S sub N equations

In this paper two new angular differencing schemes for use in spheres are derived and examined. These two schemes are the standard linear discontinuous (SLD) scheme and a hybrid scheme. In the hybrid scheme the angular flux is assumed to be quadratic and continuous in the angular cell whose boundary is the starting direction ({mu} = {minus}1) and SLD in all other angular cells. The hybrid scheme is called the LDQ scheme. For smooth problems, both schemes are shown to exhibit fourth-order conver… more

Date: January 1, 1991

Creator: Walters, W. F. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Coupled proton/neutron transport calculations using the S sub N and Monte Carlo methods

Coupled charged/neutral article transport calculations are most often carried out using the Monte Carol technique. For example, the ITS, EGS, and MCNP (Version 4) codes are used extensively for electron/photon transport calculations while HETC models the transport of protons, neutrons and heavy ions. In recent years there has been considerable progress in deterministic models of electron transport, and many of these models are applicable to protons. However, even with these new models (and the … more

Date: January 1, 1991

Creator: Filippone, W. L. (Arizona Univ., Tucson, AZ (USA). Dept. of Nuclear and Energy Engineering); Little, R. C.; Morel, J. E.; MacFarlane, R. E. & Young, P. G. (Los Alamos National Lab., NM (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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An Even-Parity/Odd-Parity Formulation for Deterministic Transport Calculations on Massively Parallel Computers

We have developed a highly parallel deterministic method for performing time-dependent particle (neutron, gamma-ray, or thermal radiation) transport calculations on arbitrarily connected 3-D tetrahedral meshes. The standard discrete-ordinates method, which is used to solve the first-order form of the transport equation, is extremely cumbersome to apply on such meshes and is based upon a mesh sweeping algorithm that is highly sequential in nature. A serial 1-D code for the CRAY-YMP and a paralle… more

Date: January 1, 1990

Creator: Morel, J. E.; Olvey, Laura A.; Claborn, G. W. & Josef, J. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Asymptotic derivation of the modified time-dependent SP{sub 2} equations and numerical calculations

Converting the independent variables of the transport equation to dimensionless parameters, asymptotic analyses can be performed to show that, for an important class of problems, the diffusion equation is an asymptotic limit of the transport equation. A recent paper by Larsen, McGhee, and Morel provides a broadened view of the result discussed above. It deals with the steady-state transport equation and shows that the Simplified Spherical-Harmonics (SP{sub N}) equations are robust high-order as… more

Date: July 1, 1993

Creator: Shin, Uncheol; Miller, W. F. Jr. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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A 3-D time-dependent unstructured tetrahedral-mesh SP{sub N} method

We have developed a 3-D time-dependent multigroup SP{sub n} method for unstructured tetrahedral meshes. The SP{sub n} equations are expressed in a canonical form which allows them to be solved using standard diffusion solution techniques in conjunction with source iteration, diffusion-synthetic acceleration, and fission-source acceleration. A computational comparison of our SP{sub n} method with an even-parity S{sub n} method is given.

Date: October 1, 1994

Creator: Morel, J. E.; McGhee, J. M. & Larsen, E. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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PLASMX: multigroup ionization and charge exchange cross-section code for neutral hydrogen transport in plasmas

PLASMX generates effective multigroup macroscopic cross sections for discrete-ordinates calculations of neutral hydrogen atom transport in tokamak systems. The effective microscopic cross sections can be generated at the midpoint energies of the multigroup bin structure. Variable dimensioning presently restricts the number of energy groups to 22, the number of spatial regions to 10, and the number of Legendre polynomial moments to 7 (P/sub 6/). (MOW)

Date: January 1, 1977

Creator: Morel, J. E. & Wienke, B. R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Asymptotic derivation of the simplified P{sub n} equations

The diffusion and simplified P{sub N} equations are derived from the transport equation by means of an asymptotic expansion in which the diffusion equation is the leading order approximation and the simplified P{sub N} equations are higher-order approximations. In addition, the simplified P{sub N} equations are reformulated in a ``canonical`` form that greatly facilitates the formulation of boundary conditions and the implementation of the resulting problem in a conventional multigroup diffusio… more

Date: February 1, 1993

Creator: Larsen, E. W.; Morel, J. E. & McGhee, J. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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A S{sub 2}-like acceleration method for the Nonlinear Characteristic transport scheme

Recently a nonlinear spatial differencing scheme for solving the discrete-ordinate equations was introduced. This scheme, referred to as the Nonlinear Characteristic (NC) scheme, is accurate for both optically thin and optically thick spatial meshes and is strictly positive. The NC discrete-ordinate equations can be solved using the source iteration (SI) method. It is well known that the SI method converges infinitely slowly for optically thick problems with scattering ratios near unity. In thi… more

Date: August 1, 1994

Creator: Wareing, T. A.; Walters, W. F. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Improved approximations applied to the S{sub N} even-parity equation

We have developed various finite element differencing schemes by applying lumping techniques in neutron streaming and removal terms of the S{sub N} even-parity transport equation in two-dimensional x-y geometry. We have derived an analytical form of the even-parity reflective boundary condition, which along with the vacuum boundary condition can be applied directly to solve second-order even-parity boundary value problems. We have also developed a new simplified even-parity equation that is muc… more

Date: July 1, 1993

Creator: Noh, Taewan, Miller, W. F. Jr. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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On the degraded effectiveness of diffusion synthetic acceleration for multidimensional sn calculations in the presence of material discontinuities

We investigate the degradation in performance of diffusion synthetic acceleration (DSA) methods in problems with discontinuities in material properties. A loss in the effectiveness of DSA schemes has been Observed before with other discretizations in two dimensions under certain conditions. We present more evidence in support of the conjecture that DSA effectiveness can degrade in multidimensional problems with discontinuities in total cross section, regardless of the particular physical config… more

Date: January 1, 2002

Creator: Warsa, J. S. (James S.); Wareing, T. A. (Todd A.) & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Krylov subspace iterations for the calculation of K-Eigenvalues with sn transport codes

We apply the Implicitly Restarted Arnoldi Method (IRAM), a Krylov subspace iterative method, to the calculation of k-eigenvalues for criticality problems. We show that the method can be implemented with only modest changes to existing power iteration schemes in an SN transport code. Numerical results on three dimensional unstructured tetrahedral meshes are shown. Although we only compare the IRAM to unaccelerated power iteration, the results indicate that the IRAM is a potentially efficient and… more

Date: January 1, 2002

Creator: Warsa, J. S. (James S.); Wareing, T. A. (Todd A.); Morel, J. E.; McGhee, J. M. (John M.) & Lehoucq, R. B. (Richard B.)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Krylov iterative methods applied to multidimensional S[sub n] calculations in the presence of material discontinuities

We show that a Krylov iterative meihod, preconditioned with DSA, can be used to efficiently compute solutions to diffusive problems with discontinuities in material properties. We consider a lumped, linear discontinuous discretization of the S N transport equation with a 'partially consistent' DSA preconditioner. The Krylov method can be implemented in terms of the original S N source iteration coding with little modification. Results from numerical experiments show that replacing source iterat… more

Date: January 1, 2002

Creator: Warsa, J. S. (James S.); Wareing, T. A. (Todd A.) & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Self-Adjoint Angular Flux Equation for Coupled Electron-Photon Transport

Recently, Morel and McGhee described an alternate second-order form of the transport equation called the self adjoint angular flux (SAAF) equation that has the angular flux as its unknown. The SAAF formulation has all the advantages of the traditional even- and odd-parity self-adjoint equations, with the added advantages that it yields the full angular flux when it is numerically solved, it is significantly easier to implement reflective and reflective-like boundary conditions, and in the appro… more

Date: July 8, 1999

Creator: Liscum-Powell, J. L.; Lorence, L. J., Jr.; Morel, J. E. & Prinja, A. K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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A diffusion accelerated solution method for the nonlinear characteristic scheme

Recently the nonlinear characteristic scheme for spatially discretizing the discrete-ordinate equations was introduced. This scheme is accurate for both optically thin and optically thick spatial meshes and produces strictly positive angular and scalar fluxes. The nonlinear characteristic discrete-ordinate equations can be solved using the source iteration method; however, it is well known that the this method converges prohibitively slowly for optically thick problems with scattering ratios at… more

Date: February 1, 1995

Creator: Wareing, T. A.; Walters, W. F. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Asymptotic derivation of the multigroup P{sub 1} and Simplified P{sub N} equations with anisotropic scattering

The multigroup and P{sub 1} and Simplified P{sub N} equations are shown to be a family of asymptotic approximation to the multigroup transport equation with anisotropic scattering. The physical assumptions are that the material system is optically thick, the probability of absorption is small, and the mean scattering angle {anti {mu}}{sub o} is not close to unity.

Date: October 1, 1994

Creator: Larsen, E. W.; Morel, J. E. & McGhee, J. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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3-D research transport codes at Los Alamos

We describe 3-D research transport codes which have been developed at Los Alamos National Laboratory over the last three years. Some simple example calculations are presented.

Date: October 1, 1994

Creator: Morel, J. E.; McGhee, J. M. & Walters, W. F.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Asymptotic analysis of the several competitive equations to solve the time-dependent neutron transport equation

Using conventional diffusion limit analysis, we asymptotically compare three competitive time-dependent equations (the telegrapher`s equation, the time-dependent Simplified P{sub 2} (SP{sub 2}) equation, and the time-dependent Simplified Evcn-Parity (SEP) equation). The time-dependent SP{sub 2} equation contains higher order asymptotic approximations of the time-dependent transport equation than the other equations in a physical regime in which the time-dependent diffusion equation is the leadi… more

Date: October 1, 1994

Creator: Shin, U.; Miller, W. F. Jr. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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ONEBFP development issues

ONEBFP is a 1-D discrete-ordinates coupled electron-photon transport code that was recently developed to replace the ONELD code. The reasons for this replacement are explained in terms of a comparison of the programming structure and numerics of the two codes.

Date: October 1, 1996

Creator: Morel, J. E. & Walters, W. F.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Discontinuous Finite Element S{sub N} Methods on 3-D Unstructured Grids

Discontinuous finite element methods for the S{sub N} equations on 3-D unstructured tetrahedral and hexahedral meshes are presented. Solution Techniques including Source Iteration and diffusion-synthetic acceleration are described. Numerical results are presented which demonstrate the accuracy and efficiency of these methods.

Date: September 27, 1999

Creator: Wareing, T. A.; McGhee, J. M.; Morel, J. E. & Pautz, S. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Positive Scattering Cross Sections using Constrained Least Squares

A method which creates a positive Legendre expansion from truncated Legendre cross section libraries is presented. The cross section moments of order two and greater are modified by a constrained least squares algorithm, subject to the constraints that the zeroth and first moments remain constant, and that the standard discrete ordinate scattering matrix is positive. A method using the maximum entropy representation of the cross section which reduces the error of these modified moments is also … more

Date: September 27, 1999

Creator: Dahl, J. A.; Ganapol, B. D. & Morel, J. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Nested Acceleration Algorithm for Self-Adjoint Angular Flux Boltxmann-CSD Equation

No Description Available.

Date: June 30, 2000

Creator: Powell, Jennifer L.; Prinja, A. K.; Morel, J. E. & Lorence, Leonard

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Monte Carlo solution of a semi-discrete transport equation

The authors present the S{sub {infinity}} method, a hybrid neutron transport method in which Monte Carlo particles traverse discrete space. The goal of any deterministic/stochastic hybrid method is to couple selected characters from each of the methods in hopes of producing a better method. The S{sub {infinity}} method has the features of the lumped, linear-discontinuous (LLD) spatial discretization, yet it has no ray-effects because of the continuous angular variable. They derive the S{sub {in… more

Date: September 1, 1999

Creator: Urbatsch, T. J.; Morel, J. E. & Gulick, J. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Diffusion Synthetic Acceleration Method for the S{sub N} Equations with Discontinuous Finite Element Space and Time Differencing

A diffusion synthetic acceleration method is developed for the time dependent S{sub N} equations with linear discontinuous finite element time differencing and discontinuous finite element spatial differencing on unstructured grids. Both theoretical and computational results are given which demonstrate the effectiveness and efficiency of the method.

Date: September 27, 1999

Creator: Wareing, T. A.; Morel, J. E. & McGhee, J. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department