Stability condition for solving convection equation by FDM

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Discussion Overview

The discussion revolves around the stability conditions for solving the convection equation using Finite Difference Methods (FDM). Participants explore whether a specific stability condition exists for the convection equation, separate from the established conditions for the Convection-Diffusion equation.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant states a known stability condition for the Convection-Diffusion equation, questioning if a similar condition exists for the convection equation alone.
  • Another participant suggests that the stability criterion is dependent on the finite difference approximation of the Laplacian and questions why the same method wouldn't apply to the convection term.
  • A participant expresses uncertainty about calculating the stability condition for the convection term, noting reliance on a formula used for diffusion to ensure stability in their program.
  • One participant raises doubts about the feasibility of calculating stability for the convection term, mentioning that stability for the diffusion equation is derived using Fourier series and that constant velocity may be necessary for accurate calculations.
  • This participant also notes the numerical challenges associated with advecting a field over long time limits and inquires about the specific application of advection.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the existence or calculation of a stability condition for the convection equation. Multiple viewpoints and uncertainties remain regarding the applicability of existing methods and the challenges of numerical stability in convection problems.

Contextual Notes

Limitations include the dependence on the finite difference approximation and the potential requirement for constant velocity in stability calculations. The discussion also highlights unresolved challenges in numerical advection over extended time periods.

nazmulislam
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Hi,

I know, there is a stability condition for solving the Convection-Diffusion equation by Finite Difference explicit/implicit technique, which is \Delta t<=(\Delta x)^2/(2*D) for one-dimensional or \Delta t<=((\Delta x)^2+(\Delta y)^2)/(8*D) for two-dimensional problem, where D is the diffusion coefficient.
.
Is there any such condition for only the convection equation?

Thanks
 
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The stability criterion is dependent on your FD approximation of the laplacian. Have you tried calculating the stability conditions? I am not sure why the same method wouldn't work for the convection term. I have not done it for the convection though.
 
Thanks for your response. I am not sure how to calculate the stability condition. I have used the the formula \Delta t<=((\Delta x)^2+(\Delta y)^2)/(8*D) to make my program stable. But if there is no diffusion term,only convection term, how will I calculate the stability condition?

Thanks
 
After some thought I am not even sure you can do the calculation with the convection term, since the stability of the diffusion equation is calculated using a Fourier series. Unless the velocity is constant i suppose things will not work that well.
Further more as far as I remember just advecting a field is not so easy numerically due to various problems(at least not in the long time limit). What are you advecting by the way? An interface? This article discusses a bit about passiv advection
http://www.ias.ac.in/sadhana/Pdf2009Apr/271.pdf

I think it is nice enough.(and eq 2 might be what you are looking for).
 
Thanks.
 

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