Menu

Discussion Forum

New Discussion
Filtern

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Time dependent study convergence

Posted 04.01.2013, 05:46 GMT-5 Studies & Solvers Version 4.3 3 Replies

SMHH
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi,

I am trying to model laminar fluid flow, heat transfer in fluids, and mass diffusion simultaneously in comsol using transient solver. The problem is that when I put the upper limit for time 1 (range: 0:0.01:1) I get this error:

"Repeated error test failures. May have reached a singularity.
Time : 0
Last time step is not converged."

But, when I increase the upper limit to 7 (range: 0:0.01:7), the solution converges without any problem or errors! This is strange since the only change to the problem is the upper limit for time.

I need to know what is the problem. Thanks in advance.

SMHH
3 Replies Last Post 04.01.2013, 07:49 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 04.01.2013, 05:57 GMT-5
Hi

what kind of time stepping are you using ? if its BDF "Free" COMSOL does not calculate for all values you give, but decides on the model variables, this may make some differences, particularly for the early steps with "poor" initial conditions (check the log, and look at the steps and the "out" messages, if you have several adjacent "out" without an explicit calculation in between then COMSOL is interpolating the results, this does not necessarily mean the results are wrong, all depends on what you are doing ;)

Try a strict or intermediate instead of the "free"

--
Good luck
Ivar
Hi what kind of time stepping are you using ? if its BDF "Free" COMSOL does not calculate for all values you give, but decides on the model variables, this may make some differences, particularly for the early steps with "poor" initial conditions (check the log, and look at the steps and the "out" messages, if you have several adjacent "out" without an explicit calculation in between then COMSOL is interpolating the results, this does not necessarily mean the results are wrong, all depends on what you are doing ;) Try a strict or intermediate instead of the "free" -- Good luck Ivar
SMHH
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 04.01.2013, 07:42 GMT-5
Hi Ivar,

Thanks for your reply. I tried BDF with strict and intermediate, but the problem is still consistent. I also tried other time domain decomposition method (Generalized alpha) with auto, and manual time stepping. But no use in doing so.

SMHH
Hi Ivar, Thanks for your reply. I tried BDF with strict and intermediate, but the problem is still consistent. I also tried other time domain decomposition method (Generalized alpha) with auto, and manual time stepping. But no use in doing so. SMHH
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 04.01.2013, 07:49 GMT-5
Hi

then I would propose that you look closer to your initial conditions and your mesh density, are they coherent with your model, are you adding "strong transients" at t=0 ?

--
Good luck
Ivar
Hi then I would propose that you look closer to your initial conditions and your mesh density, are they coherent with your model, are you adding "strong transients" at t=0 ? -- Good luck Ivar

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content