Dissertation/Thesis Abstract

The quasidiffusion method for transport problems on unstructured meshes
by Wieselquist, William A., Ph.D., North Carolina State University, 2009, 211; 3360623
Abstract (Summary)

In this work, we develop a quasidiffusion (QD) method for solving radiation transport problems on unstructured quadrilateral meshes in 2D Cartesian geometry, for example hanging-node meshes from adaptive mesh refinement (AMR) applications or skewed quadrilateral meshes from radiation hydrodynamics with Lagrangian meshing. The main result of the work is a new low-order quasidiffusion (LOQD) discretization on arbitrary quadrilaterals and a strategy for the efficient iterative solution which uses Krylov methods and incomplete LU factorization (ILU) preconditioning. The LOQD equations are a non-symmetric set of first-order PDEs that in second-order form resembles convection-diffusion with a diffusion tensor, with the difference that the LOQD equations contain extra cross-derivative terms. Our finite volume (FV) discretization of the LOQD equations is compared with three LOQD discretizations from literature.

We then present a conservative, short characteristics discretization based on subcell balances (SCSB) that uses polynomial exponential moments to achieve robust behavior in various limits (e.g. small cells and voids) and is second-order accurate in space. A linear representation of the isotropic component of the scattering source based on face-average and cell-average scalar fluxes is also proposed and shown to be effective in some problems.

In numerical tests, our QD method with linear scattering source representation shows some advantages compared to other transport methods. We conclude with avenues for future research and note that this QD method may easily be extended to arbitrary meshes in 3D Cartesian geometry.

Indexing (document details)
Advisor: Anistratov, Dmitriy Y.
School: North Carolina State University
School Location: United States -- North Carolina
Source: DAI-B 70/05, Dissertation Abstracts International
Subjects: Nuclear engineering, Astronomy
Keywords: Arbitrary quadrilaterals, Cartesian, Characteristic methods, Particle transport, Quasidiffusion, Radiation transport, Subcell balance, Unstructured meshes
Publication Number: 3360623
ISBN: 978-1-109-18344-3
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