Volume 40, Issue 6
Stable Boundary Conditions and Discretization for $P_N$ Equations

J. Comp. Math., 40 (2022), pp. 977-1003.

Published online: 2022-08

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• Abstract

A solution to the linear Boltzmann equation satisfies an energy bound, which reflects a natural fact: The energy of particles in a finite volume is bounded in time by the energy of particles initially occupying the volume augmented by the energy transported into the volume by particles entering the volume over time. In this paper, we present boundary conditions (BCs) for the spherical harmonic $(P_N)$ approximation, which ensure that this fundamental energy bound is satisfied by the $P_N$ approximation. Our BCs are compatible with the characteristic waves of $P_N$ equations and determine the incoming waves uniquely. Both, energy bound and compatibility, are shown on abstract formulations of $P_N$ equations and BCs to isolate the necessary structures and properties. The BCs are derived from a Marshak type formulation of BC and base on a non-classical even/odd-classification of spherical harmonic functions and a stabilization step, which is similar to the truncation of the series expansion in the $P_N$ method. We show that summation by parts (SBP) finite difference on staggered grids in space and the method of simultaneous approximation terms (SAT) allows to maintain the energy bound also on the semi-discrete level.

35B35, 35Q20, 35L50, 65M06, 65M12, 65M70

buenger@acom.rwth-aachen.de (Jonas Bünger)

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@Article{JCM-40-977, author = {Bünger , JonasSarna , Neeraj and Torrilhon , Manuel}, title = {Stable Boundary Conditions and Discretization for $P_N$ Equations}, journal = {Journal of Computational Mathematics}, year = {2022}, volume = {40}, number = {6}, pages = {977--1003}, abstract = {

A solution to the linear Boltzmann equation satisfies an energy bound, which reflects a natural fact: The energy of particles in a finite volume is bounded in time by the energy of particles initially occupying the volume augmented by the energy transported into the volume by particles entering the volume over time. In this paper, we present boundary conditions (BCs) for the spherical harmonic $(P_N)$ approximation, which ensure that this fundamental energy bound is satisfied by the $P_N$ approximation. Our BCs are compatible with the characteristic waves of $P_N$ equations and determine the incoming waves uniquely. Both, energy bound and compatibility, are shown on abstract formulations of $P_N$ equations and BCs to isolate the necessary structures and properties. The BCs are derived from a Marshak type formulation of BC and base on a non-classical even/odd-classification of spherical harmonic functions and a stabilization step, which is similar to the truncation of the series expansion in the $P_N$ method. We show that summation by parts (SBP) finite difference on staggered grids in space and the method of simultaneous approximation terms (SAT) allows to maintain the energy bound also on the semi-discrete level.

}, issn = {1991-7139}, doi = {https://doi.org/10.4208/jcm.2104-m2019-0231}, url = {http://global-sci.org/intro/article_detail/jcm/20844.html} }
TY - JOUR T1 - Stable Boundary Conditions and Discretization for $P_N$ Equations AU - Bünger , Jonas AU - Sarna , Neeraj AU - Torrilhon , Manuel JO - Journal of Computational Mathematics VL - 6 SP - 977 EP - 1003 PY - 2022 DA - 2022/08 SN - 40 DO - http://doi.org/10.4208/jcm.2104-m2019-0231 UR - https://global-sci.org/intro/article_detail/jcm/20844.html KW - Boundary conditions, Energy stability, Spherical harmonic ($P_N$) approximation, Kinetic theory, Moment method, Boltzmann, Linear transport. AB -

A solution to the linear Boltzmann equation satisfies an energy bound, which reflects a natural fact: The energy of particles in a finite volume is bounded in time by the energy of particles initially occupying the volume augmented by the energy transported into the volume by particles entering the volume over time. In this paper, we present boundary conditions (BCs) for the spherical harmonic $(P_N)$ approximation, which ensure that this fundamental energy bound is satisfied by the $P_N$ approximation. Our BCs are compatible with the characteristic waves of $P_N$ equations and determine the incoming waves uniquely. Both, energy bound and compatibility, are shown on abstract formulations of $P_N$ equations and BCs to isolate the necessary structures and properties. The BCs are derived from a Marshak type formulation of BC and base on a non-classical even/odd-classification of spherical harmonic functions and a stabilization step, which is similar to the truncation of the series expansion in the $P_N$ method. We show that summation by parts (SBP) finite difference on staggered grids in space and the method of simultaneous approximation terms (SAT) allows to maintain the energy bound also on the semi-discrete level.

Jonas Bünger, Neeraj Sarna & Manuel Torrilhon. (2022). Stable Boundary Conditions and Discretization for $P_N$ Equations. Journal of Computational Mathematics. 40 (6). 977-1003. doi:10.4208/jcm.2104-m2019-0231
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