CFD Online Logo CFD Online URL
Home > Forums > OpenFOAM Running, Solving & CFD

How force solver to update variable with nearly diagonal matrix

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Display Modes
Old   February 29, 2008, 04:52
Default Hi, I'm solving an electric
Ola Widlund
Join Date: Mar 2009
Location: Sweden
Posts: 87
Rep Power: 10
olwi is on a distinguished road

I'm solving an electric problem, with generation of negative and positive charge carriers. The negative charges (electrons) have a mobility (~velocity) 1e5 times larger than the positive charges (ions). It means that when a molecule is ionized, the positive ion stays where it is, but the electron is leaving the scene very quickly...

I obviously need to solve on the time-scale of the fast electrons. I would like to solve the transport equations for both electrons and ions. Problem is that the physics for the ions is almost compleletly local on that time scale, and the matrix is nearly diagonal.

I could in principle live without the convection and diffusion terms in the slow equations and solve the resulting ODE:s, but that means I need to learn how to do that in OF, and it would be more neat to treat the equations the same.

After this preamble, my questions:

1) It seems an fvMatrix refuses to solve if there are no spatial operators. Is there any way or any solver that could be forced to update the resulting ODE, without rewriting the code?

2) If I do include my very slow spatial operators, the solver finds so little work to do in each timestep, that it often refuses to iterate. This means that the ions produced in that timestep just dissappears, as no update is done. (i) Is lowering the aboslute tolernace to exetremly small numbers the only way to make it crunch? (ii) Is there any solver that can be set to do at least ONE iteration, always?

Apologize for the long post, but still hope someone read all the way...

Thanks in advance for any ideas,

olwi is offline   Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
fast penta diagonal solver sudhakar Main CFD Forum 8 August 23, 2007 12:20
Matrix solver Yang Main CFD Forum 5 May 13, 2006 22:20
udf ,,, matrix solver!!! ozgun FLUENT 0 May 7, 2006 13:01
particle body force and scalar update. Kasper Skriver FLUENT 1 March 21, 2006 10:55
Penta-Diagonal matrix solver Jaswant Main CFD Forum 2 July 19, 2005 23:40

All times are GMT -4. The time now is 18:59.