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

Relative Tolerance

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

LinkBack Thread Tools Display Modes
Old   June 1, 2009, 22:31
Default Relative Tolerance
New Member
Rachel Harch
Join Date: Mar 2009
Location: RAdelaide
Posts: 2
Rep Power: 0
RachelElizabeth is on a distinguished road
I was wondering if someone could help me to understand the details of relTol.

I am unsure which has the stricter convergence criteria relTol=0.1 or relTol=0.001.

I understand that if you set relTol=0 that you force the solution to converge to the solver tolerance, but I am not sure about other values.

RachelElizabeth is offline   Reply With Quote

Old   June 4, 2009, 10:56
Senior Member
Rishi .
Join Date: Mar 2009
Posts: 144
Rep Power: 10
hellorishi is on a distinguished road

relTol is a parameter to say how much the intial residual should reduce in a particular time step.

e.g. relTol=0, then default tolerence is targetted. (e-6 here)
DICPCG: Solving for p, Initial residual = 1, Final residual = 7.55402e-07, No Iterations 35
DICPCG: Solving for p, Initial residual = 0.379232, Final residual = 3.38648e-07, No Iterations 34

e.g. relTol=0.01, then solver only tries to reduce residual by certain factor. This relTol is the order of magnitude reduction. So here Solver tries to reach a value below 1/100 of initial value.
DICPCG: Solving for p, Initial residual = 1, Final residual = 0.00837542, No Iterations 24
DICPCG: Solving for p, Initial residual = 0.378888, Final residual = 0.00355735, No Iterations 23

So relTol=0.001 is stricter criteria & requires more iterations. Observe the number of iterations required in the above examples, for the same calculation.
hellorishi 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
relative humidity and temperature by outlet Bing FLUENT 5 March 7, 2014 07:03
Relative humidity amar FLUENT 0 April 14, 2009 20:59
Tolerance in GAMBIT Help!!!!!! Lottar FLUENT 0 October 6, 2008 14:03
Relative Error in Grid Convergence Christopher Haugh Main CFD Forum 2 March 9, 2007 13:42
RELATIVE STREAMLINES !! ozgur FLUENT 0 March 25, 2004 21:34

All times are GMT -4. The time now is 07:53.