296 research outputs found
Development of High-Order P\u3cem\u3e\u3csub\u3eN\u3c/sub\u3e\u3c/em\u3e Models for Radiative Heat Transfer in Special Geometries and Boundary Conditions
The high-order spherical harmonics () method for 2-D Cartesian domains is extracted from the 3-D formulation. The number of equations and intensity coefficients reduces to (N+1)2/4 in the 2-D Cartesian formulation compared with N(N+1)/2 for the general 3-D formulation. The Marshak boundary conditions are extended to solve problems with nonblack and mixed diffuse-specular surfaces. Additional boundary conditions for specified radiative wall flux, for symmetry/specular reflection boundaries have also been developed. The mathematical details of the formulations and their implementation in the OpenFOAM finite volume based CFD software platform are presented. The accuracy and computational cost of the 2-D Cartesian are compared with that of the 3-D solver and a Photon Monte Carlo solver for a square enclosure, as well as a 45° wedge geometry with variable radiative properties. The new boundary conditions have been applied for both test cases, and the boundary condition for mixed diffuse-specular surfaces is further illustrated by numerical examples of a rectangular geometry enclosed by walls with different surface characteristics
A convergent method for linear half-space kinetic equations
We give a unified proof for the well-posedness of a class of linear
half-space equations with general incoming data and construct a Galerkin method
to numerically resolve this type of equations in a systematic way. Our main
strategy in both analysis and numerics includes three steps: adding damping
terms to the original half-space equation, using an inf-sup argument and
even-odd decomposition to establish the well-posedness of the damped equation,
and then recovering solutions to the original half-space equation. The proposed
numerical methods for the damped equation is shown to be quasi-optimal and the
numerical error of approximations to the original equation is controlled by
that of the damped equation. This efficient solution to the half-space problem
is useful for kinetic-fluid coupling simulations
StaRMAP - A second order staggered grid method for spherical harmonics moment equations of radiative transfer
We present a simple method to solve spherical harmonics moment systems, such
as the the time-dependent and equations, of radiative transfer.
The method, which works for arbitrary moment order , makes use of the
specific coupling between the moments in the equations. This coupling
naturally induces staggered grids in space and time, which in turn give rise to
a canonical, second-order accurate finite difference scheme. While the scheme
does not possess TVD or realizability limiters, its simplicity allows for a
very efficient implementation in Matlab. We present several test cases, some of
which demonstrate that the code solves problems with ten million degrees of
freedom in space, angle, and time within a few seconds. The code for the
numerical scheme, called StaRMAP (Staggered grid Radiation Moment
Approximation), along with files for all presented test cases, can be
downloaded so that all results can be reproduced by the reader.Comment: 28 pages, 7 figures; StaRMAP code available at
http://www.math.temple.edu/~seibold/research/starma
Convergence acceleration aspects in the solution of the PN neutron transport eigenvalue problem
The solution of the eigenvalue problem for neutron transport is of utmost importance in
the field of reactor physics, and represents a challenging problem for numerical models.
Different eigenvalue formulations can be identified, each with its own physical significance.
The numerical solution of these problems by deterministic methods requires the
introduction of approximations, such as the spherical harmonics expansion in PN models,
leading to results that depend on the approximations introduced (spatial mesh size,
N order, ...). All these results represent, in principle, sequences that can easily profit
from acceleration techniques to approach convergence towards the correct value. Such a
reference value is estimated, in this work, by the Monte Carlo technique. The Wynn-
acceleration method is applied to the various sequences of eigenvalues emerging when
tackling the solution of the PN models with different orders and increasing spatial accuracy,
in order to obtain more accurate, benchmark-quality results. It is shown that the
acceleration can be successfully applied and that the analysis of the results of different acceleration approaches sheds some light on the physical meaning of the numerical approximations
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