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Model convergence issue

Posted Jun 18, 2015, 2:40 p.m. EDT Fluid & Heat, Porous Media Flow, Geometry, Mesh, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers 4 Replies

Syed Zaid Ali
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Hello everyone

I am conducting a time dependent study. My model converges for smaller time scales viz range(10^-12,10^-6,1.1354e-5) . However, when I run the study for a larger range, which is
range(10^-12,10^-4,10^-2), the model does not achieve convergence and gives an error.

If anybody could guide me what the problem might be, I will be obliged.

Thank you
Zaid
4 Replies Last Post Sep 18, 2015, 12:45 p.m. EDT
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Hello Syed Zaid Ali

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Sepideh Ramezani
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Posted: 9 years ago Sep 10, 2015, 4:28 a.m. EDT
Hi,

I have the same problem, my model converge for smaller time step (0,0.1,1) but not for bigger time study (0,3600,3870000).

Did you solve your problem?
Is there any general solution for solving this problem?

Hope to hear answer.
Thanks
Sepideh
Hi, I have the same problem, my model converge for smaller time step (0,0.1,1) but not for bigger time study (0,3600,3870000). Did you solve your problem? Is there any general solution for solving this problem? Hope to hear answer. Thanks Sepideh
Syed Zaid Ali
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Posted: 9 years ago Sep 10, 2015, 6:22 a.m. EDT
Hello Sapideh

You can try by decreasing the time step. This will ofcourse take longer time to converge but it will make sure that the jump while finding the optimum solution is not very high.

Best regards
Zaid
Hello Sapideh You can try by decreasing the time step. This will ofcourse take longer time to converge but it will make sure that the jump while finding the optimum solution is not very high. Best regards Zaid
Sepideh Ramezani
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Posted: 9 years ago Sep 10, 2015, 8:47 a.m. EDT
Hi,

Thanks for reply, but even if I reduce the time step to the half 1800 or even 60[s], it is not converging.

Is there anyway to change the setting for the BDF solver? because I saw in the Time dependent solver, time stepping, there are two sections by choosing: initial step and maximum step.


Is there anybody know how this time stepping section is working for the large models?

Hope to hear answer,
Thanks
Sepideh
Hi, Thanks for reply, but even if I reduce the time step to the half 1800 or even 60[s], it is not converging. Is there anyway to change the setting for the BDF solver? because I saw in the Time dependent solver, time stepping, there are two sections by choosing: initial step and maximum step. Is there anybody know how this time stepping section is working for the large models? Hope to hear answer, Thanks Sepideh
Hassan Khan
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Posted: 9 years ago Sep 18, 2015, 12:45 p.m. EDT
I am facing the same problem because I am using a rectangular pulse train. However, you time range is not too long. I suggest you to change your time stepping, steps taken by solver to 'strict'.
study>solver config>solution>time dependent solver>timestepping> chose BDF> and change steps taken by solver from free to intermediate or strict.

Good luck.

Hassan.
I am facing the same problem because I am using a rectangular pulse train. However, you time range is not too long. I suggest you to change your time stepping, steps taken by solver to 'strict'. study>solver config>solution>time dependent solver>timestepping> chose BDF> and change steps taken by solver from free to intermediate or strict. Good luck. Hassan.

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