Menu

Discussion Forum

New Discussion
Filtra

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 The information provided may be out of date.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.

Undefined value found

Posted 19 ott 2009, 10:22 GMT-4 Chemical Reaction Engineering, Mesh, Studies & Solvers Version 4.3b 15 Replies

Stefan Eidelloth
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi,

i can solve my semiconductor model with a relatively coarse mesh.
However the found solution is not good enough. It shows some
differences to a reference (PC1D) semiconductor model.

That is why i want to refine the mesh.


But if i refine the mesh i get following error:

---------------------------------------------------------------------
Error: 7248
Undefined value found.

Details:
Exception:
com.femlab.jni.FlNativeException: Undefined value found Solvermodel
Messages:
Undefined value found Solvermodel

Stack trace:
at solvermodel.cpp, row 1837, (Undefined value found in the equation residual vector.
There are 85 degrees of freedom giving NaN/Inf in the vector for the variable phii
at coordinates: (0.000493076,-5.8675e-005), (0.00049406,-5.80051e-005), (0.000495044,-5.73351e-005), (0.000494026,-5.58557e-005), (0.000493041,-5.65256e-005), ...
)
at com.femlab.solver.FlSolver.femStatic(Native Method)
at com.femlab.solver.FemStatic.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)
----------------------------------------------------------------------------

The model is quite complex and has 5 coupled application modes.
I use the Parametric segregated Solver.

I think if there would be a problem with my initialisation values or boundary contitions,
i would not be able to solve the model even with a coarse mesh?

I found out, that the problem especially occurs, if i refine the mesh in a region with large gradients.

The Comsol solution is represented by green circles and the reference solution is shown as line in the attached figure.

Has anyone an idea how the finer mesh causes "undefined value"-problems and how to overcome them?

Thank you,

Stefan







Attachments:

15 Replies Last Post 22 mar 2017, 06:54 GMT-4
COMSOL Moderator

Hello Stefan Eidelloth

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Jose Enrique Paredes
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 11 mar 2010, 16:37 GMT-5
Hey, i have the same problem

i push the icon restart y works.
Hey, i have the same problem i push the icon restart y works.
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: 2 decades ago 12 mar 2010, 02:06 GMT-5
Hi

My first reaction is that you are hitting a numerical limitation (you case is a typical examples of the type I send myself to COMSOL support).

As you say, normally you should have a denser mesh where your gradients are steep

Cannot comment further
Good luck
Ivar
Hi My first reaction is that you are hitting a numerical limitation (you case is a typical examples of the type I send myself to COMSOL support). As you say, normally you should have a denser mesh where your gradients are steep Cannot comment further Good luck Ivar
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: 2 decades ago 12 mar 2010, 02:08 GMT-5
Hi

If it works on second try with a "restart" it could come from the initial conditions, since normally a restart ""re-start" from current level of already calculated results

Ivar

Hi If it works on second try with a "restart" it could come from the initial conditions, since normally a restart ""re-start" from current level of already calculated results Ivar
Nguyen Lang
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 17 mar 2010, 10:12 GMT-4
Hello Mr. Ivar
Can you give me some advice with the following errors.
Error:
Time 1.386578133869988:
Error in Jacobian computation:
Undefined_value_found_Solvermodel
Undefined value found in the stiffness matrix.
Error:
Time 5.125383036305885:
Nonlinear solver did not converge.
Last time step is not converged.
I'm looking forward to your reply.
Thank you.
N.L
Hello Mr. Ivar Can you give me some advice with the following errors. Error: Time 1.386578133869988: Error in Jacobian computation: Undefined_value_found_Solvermodel Undefined value found in the stiffness matrix. Error: Time 5.125383036305885: Nonlinear solver did not converge. Last time step is not converged. I'm looking forward to your reply. Thank you. N.L
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: 2 decades ago 18 mar 2010, 03:18 GMT-4
Hi

unfortunately no apart that forme it means you have a complex model ;)

But it looks like there is un undefined variable, so are you sure your BC are real everywhere or over the time ?

For the second it's eitherthe solver is stuck typically on a steep edge of some change, or it does not have enough steps to converge, and you should increase the maximum allowed steps

Try to split your problem, or solve just one physics to check that it is fully possible to fiond a solution in a simpler case

Good luck
Ivar
Hi unfortunately no apart that forme it means you have a complex model ;) But it looks like there is un undefined variable, so are you sure your BC are real everywhere or over the time ? For the second it's eitherthe solver is stuck typically on a steep edge of some change, or it does not have enough steps to converge, and you should increase the maximum allowed steps Try to split your problem, or solve just one physics to check that it is fully possible to fiond a solution in a simpler case Good luck Ivar
Nguyen Lang
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 18 mar 2010, 04:20 GMT-4
Hello Mr. Ivar KJELBERG
Thank you for your advice.
I sent a private message to Mr. Ivar.
Please help me.
Sincerely,
N.L
nhhieubk@gmail.com
Hello Mr. Ivar KJELBERG Thank you for your advice. I sent a private message to Mr. Ivar. Please help me. Sincerely, N.L nhhieubk@gmail.com
Nurul Hasan
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 13 apr 2010, 10:29 GMT-4
Hi Stefan
Have you got any solution to this problem?

docnurulhasan@gmail.com
Hi Stefan Have you got any solution to this problem? docnurulhasan@gmail.com
Stefan Eidelloth
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 13 apr 2010, 13:17 GMT-4
Hi,
I did not further work on that specific issue
and i did not try the "restart option",
but please keep us updated if you do.

Currently I am working on a model with a
conductive boundarie instead of a resolved emitter.
This way I can avoid high gradients.

Best regards,
Stefan
Hi, I did not further work on that specific issue and i did not try the "restart option", but please keep us updated if you do. Currently I am working on a model with a conductive boundarie instead of a resolved emitter. This way I can avoid high gradients. Best regards, Stefan
Leonardo Babun
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 13 apr 2010, 16:55 GMT-4
Hello All..!!!

I was having the same problem And I could fix it changing the Intial Value and the Values of variables not solved Option inside the Solver Manager...this may be happening because You have selected "Zero" for Variables not Solved option...try this way and let me know the results...

Leo

Hello All..!!! I was having the same problem And I could fix it changing the Intial Value and the Values of variables not solved Option inside the Solver Manager...this may be happening because You have selected "Zero" for Variables not Solved option...try this way and let me know the results... Leo
Wei Liu
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 16 apr 2010, 09:34 GMT-4
I had the same problem.

The reason is possibly that initial value is zero in the first calculation step. I changed the initial value from zero to a expression not Zero.

It worked.


I had the same problem. The reason is possibly that initial value is zero in the first calculation step. I changed the initial value from zero to a expression not Zero. It worked.
Aaron Quastel
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 2 decades ago 23 lug 2010, 17:04 GMT-4
I had this problem as well in my 3D model. Initially I thought this was a mesh problem and that I need only refine it. This though did not correct the problem. Reading the above comments I set the 'Initial value' in the Solver Manager window to 'Initial value expression' instead of 'Initial value expression evaluated using current solution'. I then provided initial values in all application modes (as well as weak form terms that I specifically defined) before running the model and this seemed to work.
Cheers

Aaron
RMC
Canada
I had this problem as well in my 3D model. Initially I thought this was a mesh problem and that I need only refine it. This though did not correct the problem. Reading the above comments I set the 'Initial value' in the Solver Manager window to 'Initial value expression' instead of 'Initial value expression evaluated using current solution'. I then provided initial values in all application modes (as well as weak form terms that I specifically defined) before running the model and this seemed to work. Cheers Aaron RMC Canada
Roopesh Mohandas Syamaladevi
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 4 nov 2010, 11:15 GMT-4
I am facing a similar problem now. I am trying to couple heat and mass transfer in a transient problem. For mass transfer, there is drastic difference in concentrations between subdomains. In one of the boundaries, sublimation is assigned. Please find the attached file. I set the 'Initial value' in the Solver Manager window to 'Initial value expression' and it did not work. I tried to do using stationary solver and store the values. However that also didn't work.

Thank you so much for your time.

Roopesh
I am facing a similar problem now. I am trying to couple heat and mass transfer in a transient problem. For mass transfer, there is drastic difference in concentrations between subdomains. In one of the boundaries, sublimation is assigned. Please find the attached file. I set the 'Initial value' in the Solver Manager window to 'Initial value expression' and it did not work. I tried to do using stationary solver and store the values. However that also didn't work. Thank you so much for your time. Roopesh

Attachments:

Gerard Santillan
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 25 gen 2012, 06:58 GMT-5
Hi Stefan,

I am having the same problem, and I am also trying to solve a model for semiconductor. Can we share our experience doing this?

You can write me to gsantil@ieee.org

According to my lectures, there two options that I have to test:

- to modify the initial values.

- To modify the mesh.

I am trying both options, but without obtaining good results until now.

Best regards.

Gerard Franz
Hi Stefan, I am having the same problem, and I am also trying to solve a model for semiconductor. Can we share our experience doing this? You can write me to gsantil@ieee.org According to my lectures, there two options that I have to test: - to modify the initial values. - To modify the mesh. I am trying both options, but without obtaining good results until now. Best regards. Gerard Franz
Stefan Eidelloth
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 25 gen 2012, 08:39 GMT-5
Hi Gerard,

it is long time ago I worked on that issue. You might try to have an initial value expression with non-zero slope (if you did not already do so). And you might want to have a look at our CoBoGUI:

www.isfh.de/institut_solarforschung/software.php?_l=1

It uses a model where diffused regions are simplified to special boundary conditions.

Good luck,

Stefan
Hi Gerard, it is long time ago I worked on that issue. You might try to have an initial value expression with non-zero slope (if you did not already do so). And you might want to have a look at our CoBoGUI: http://www.isfh.de/institut_solarforschung/software.php?_l=1 It uses a model where diffused regions are simplified to special boundary conditions. Good luck, Stefan
Nicolaas Engelbrecht
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 22 mar 2017, 06:54 GMT-4
Updated: 8 years ago 19 mag 2017, 12:53 GMT-4
.
.

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