COMSOL Forums: Undefined value found

Re: Undefined value found

Wed, 25 Jan 2012 12:39:24 +0000

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

Re: Undefined value found

Wed, 25 Jan 2012 10:58:06 +0000

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

Re: Undefined value found, error 7248

Thu, 04 Nov 2010 14:15:14 +0000

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

Re: Undefined value found, error 7248

Fri, 23 Jul 2010 19:04:54 +0000

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

Re: Undefined value found

Fri, 16 Apr 2010 11:34:24 +0000

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.

Re: Undefined value found

Tue, 13 Apr 2010 18:55:33 +0000

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

Re: Undefined value found

Tue, 13 Apr 2010 15:17:00 +0000

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

Re: Undefined value found

Tue, 13 Apr 2010 12:29:42 +0000

Hi Stefan
Have you got any solution to this problem?

docnurulhasan@gmail.com

Re: Undefined value found

Thu, 18 Mar 2010 07:20:07 +0000

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

Re: Undefined value found

Thu, 18 Mar 2010 06:18:01 +0000

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

Re: Undefined value found

Wed, 17 Mar 2010 13:12:12 +0000

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

Re: Undefined value found

Fri, 12 Mar 2010 06:08:11 +0000

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

Re: Undefined value found

Fri, 12 Mar 2010 06:06:03 +0000

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

Re: Undefined value found

Thu, 11 Mar 2010 20:37:52 +0000

Hey, i have the same problem

i push the icon restart y works.

Undefined value found

Mon, 19 Oct 2009 12:22:26 +0000

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