Numerical artifacts in the Generalized Porous Medium Equation: Why harmonic averaging itself is not to blame

JOURNAL OF COMPUTATIONAL PHYSICS

卷:361

Article

Maddix, Danielle C.¹  Sampaio, Luiz²  Gerritsen, Margot^1,2 

[1] Stanford Univ, Inst Computat & Math Engn, Stanford, CA 94305 USA

[2] Stanford Univ, Energy Resources Engn, Stanford, CA 94305 USA

关键词: Generalized porous medium equation;    Degenerate nonlinear parabolic equations;    Harmonic and arithmetic averaging;    Modified equation analysis;    Temporal oscillations;    Self-sharpening;   

DOI  :  10.1016/j.jcp.2018.02.010

来源: Elsevier

【 摘 要 】

The degenerate parabolic Generalized Porous Medium Equation (GPME) poses numerical challenges due to self-sharpening and its sharp corner solutions. For these problems, we show results for two subclasses of the GPME with differentiable k(p) with respect to p, namely the Porous Medium Equation (PME) and the superslow diffusion equation. Spurious temporal oscillations, and nonphysical locking and lagging have been reported in the literature. These issues have been attributed to harmonic averaging of the coefficient k(p) for small p, and arithmetic averaging has been suggested as an alternative. We show that harmonic averaging is not solely responsible and that an improved discretization can mitigate these issues. Here, we investigate the causes of these numerical artifacts using modified equation analysis. The modified equation framework can be used for any type of discretization. We show results for the second order finite volume method. The observed problems with harmonic averaging can be traced to two leading error terms in its modified equation. This is also illustrated numerically through a Modified Harmonic Method (MHM) that can locally modify the critical terms to remove the aforementioned numerical artifacts. (C) 2018 Elsevier Inc. All rights reserved.

【 授权许可】

Free