CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Why switching time step length can help on achieving the convergence

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

LinkBack Thread Tools Display Modes
Old   December 27, 2012, 18:17
Question Why switching time step length can help on achieving the convergence
Senior Member
Anna Tian's Avatar
Meimei Wang
Join Date: Jul 2012
Posts: 494
Rep Power: 7
Anna Tian is on a distinguished road

When my simulation doesn't converge, I always change my time step to a smaller time step(or larger time step). Then after a lot of iterations, it still doesn't converge. Then I switch the time step back to what I used at the beginning. Then my simulation converges.

Could you tell me why switching time step(and then switch back) can help on the convergence? How do you explain this theoretically?

Thank you!
Best regards,
Anna Tian is offline   Reply With Quote

Old   December 27, 2012, 18:43
Senior Member
Chris DeGroot
Join Date: Nov 2011
Location: Canada
Posts: 387
Rep Power: 6
cdegroot is on a distinguished road
I am assuming you are referring to steady state simulations and that you are using timestepping for stability. Correct me if I'm wrong. Smaller timesteps make things change more slowly, making it less likely the solution will diverge or get into a situation where convergence gets stuck. However a smaller timestep will mean it will take longer to achieve a steady state solution. Thus it can be helpful to start with a small timestep to get things going in the right direction and them change to a larger one so it can actually reach steady state in a reasonable length of time.
cdegroot 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
InterFoam negative alpha karasa03 OpenFOAM 7 December 12, 2013 04:41
SLTS+rhoPisoFoam: what is rDeltaT??? nileshjrane OpenFOAM Running, Solving & CFD 4 February 25, 2013 05:13
High Courant Number @ icoFoam Artex85 OpenFOAM Running, Solving & CFD 9 January 3, 2012 09:06
Orifice Plate with a fully developed flow - Problems with convergence jonmec OpenFOAM Running, Solving & CFD 3 July 28, 2011 05:24
Time step, Number of time step, Maxximum Iterations per time step sandisk FLUENT 0 July 18, 2011 02:57

All times are GMT -4. The time now is 02:52.