CFD Online Logo CFD Online URL
Home > Forums > OpenFOAM

Help with Implicit Underrelaxation

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

LinkBack Thread Tools Display Modes
Old   July 30, 2013, 03:59
Default Help with Implicit Underrelaxation
New Member
Join Date: Feb 2013
Posts: 3
Rep Power: 4
hulk is on a distinguished road

I've got a problem understanding the implicit under-relaxation procedure of OPENFOAM. I understand that it used to insure diagonal dominance of the system Matrix, by dividing the diagonal by alpha, and adding an explicit source term to the equation.

The problem that I am having is, that in the CODE of OPENFOAM there stands something like:

// Store the current unrelaxed diagonal for use in updating the source
scalarField D0(D);

// Calculate the sum-mag off-diagonal from the interior faces
scalarField sumOff(D.size(), 0.0);

D[celli] = max(mag(D[celli]), sumOff[celli]);

// ... then relax
D /= alpha;
So as far as I understand this makes sure that the main diagonal is at least as big as the sum of all off diagonal elements in the matrix. But my main Question now is doesn't this procedure violate the consistency of discretisation of Faces (discretisation procedure is the same for both Cells sharing the face)?

My be some one can help me with this problem, or give me some hints for literature.

hulk is offline   Reply With Quote


diagonal, openfoam, underrelaxation

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
Help. implicit discritization dearboy Main CFD Forum 0 November 25, 2010 22:46
Can anyone explain the difference between these implicit concepts? bearcat Main CFD Forum 0 February 20, 2010 19:39
Euler (explicit or implicit) anybody Main CFD Forum 2 May 8, 2006 02:12
how implicit is implicit? Joe cool Main CFD Forum 7 July 16, 2004 11:10
UDF : Chemical Reaction in Catalytic Converter adhimac FLUENT 1 March 27, 2001 14:04

All times are GMT -4. The time now is 04:31.