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-   -   Conjugate-Gradient solver did not converge! (http://www.cfd-online.com/Forums/star-ccm/129024-conjugate-gradient-solver-did-not-converge.html)

sazrul January 26, 2014 21:40

Conjugate-Gradient solver did not converge!
 
Hi experts,

Currently I am running an Under hood Thermal Management analysis using Star-ccm+ v8.06.005. However, I am facing this error; 'Conjugate-Gradient solver did not converge' while I am trying to run the solution.

Can anyone tell me what does this error means? What should I do to fix it?

Your kind help is highly appreciated :).

Regards,
Sazrul
Kuala Lumpur.

ignat January 29, 2014 09:19

Quote:

Originally Posted by sazrul (Post 471908)
Hi experts,

Currently I am running an Under hood Thermal Management analysis using Star-ccm+ v8.06.005. However, I am facing this error; 'Conjugate-Gradient solver did not converge' while I am trying to run the solution.

Can anyone tell me what does this error means? What should I do to fix it?

Your kind help is highly appreciated :).

Regards,
Sazrul
Kuala Lumpur.

It is not serious problem. CG method is used for acceleration pressure solver and this message means only that your task is calculated without acceleration.

You may switch off CG and this message the following way.
Select:

Solver->Segregated Flow->Pressure->AMG Linear Solver->Acceleration method->None

sms1424 April 18, 2016 16:43

Quote:

Originally Posted by ignat (Post 472331)
It is not serious problem. CG method is used for acceleration pressure solver and this message means only that your task is calculated without acceleration.

You may switch off CG and this message the following way.
Select:

Solver->Segregated Flow->Pressure->AMG Linear Solver->Acceleration method->None

I am simulating turbulent flow inside a duct, and faced the same issue.

If I ignore the acceleration, I believe that will affect my simulation, Am I right?
Is there a way to fix this issue and get convergence w/o ignoring acceleration?

Thanks!

ignat April 19, 2016 13:36

Quote:

Originally Posted by sms1424 (Post 595642)
I am simulating turbulent flow inside a duct, and faced the same issue.

If I ignore the acceleration, I believe that will affect my simulation, Am I right?
Is there a way to fix this issue and get convergence w/o ignoring acceleration?

Thanks!

If you ignore the acceleration then that will affect on execution time only. Not solution.
If you don't want to ignore the acceleration then try to make experiments, for example decreas Under-relaxation factor.
Solver->Segregated Flow ->Velocity->Under-relaxation factor

and

Solver->Segregated Flow ->Pressure->Under-relaxation factor

Good luck!

sms1424 April 19, 2016 14:02

Quote:

Originally Posted by ignat (Post 595781)
If you ignore the acceleration then that will affect on execution time only. Not solution.
If you don't want to ignore the acceleration then try to make experiments, for example decreas Under-relaxation factor.
Solver->Segregated Flow ->Velocity->Under-relaxation factor

and

Solver->Segregated Flow ->Pressure->Under-relaxation factor

Good luck!

Thank you so much!


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