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 The information provided may be out of date.

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singularity error

Posted 02.07.2013, 14:21 GMT-4 Low-Frequency Electromagnetics, Microfluidics, Chemical Reaction Engineering, Studies & Solvers Version 4.3 4 Replies

Nancy
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Hi,

I am trying to solve a time dependent, 2D, multiphysics problem using "Transport of Diluted Species" and "Electric Current". In my model there are basically 5 domains in series: at all of them and at every time there are always diffusion, electromigration and one reaction (R1) taking place. At the second and the forth domain, there is an additional reaction(R2) that is taking place periodically. My boundary condition is no flux for any species at the surrounding walls.

When I try to solve the problem, I am getting the error:
Repeated error test failures. May have reached a singularity.
Last time step is not converged.
-Feature: Time-Dependent Solver1 (sol1/t1)
-Error: Repeated error test failures. May have reached a singularity

If I decrease the reaction rate for R2 by 10^(-6), the program runs without a problem and gives me a reasonable result. Nevertheless, these values are not real, and I need to change the parameters back to the original ones.

I read at other threads that the boundary conditions might be causing the problem. I tried to use "flux discontinuouty" at the interfaces between the domains, but without success.

Has anybody else had a similar problem? Can you please help?

Thank you in advance,
Nancy
4 Replies Last Post 30.10.2013, 13:17 GMT-4
aNdres F
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Posted: 1 decade ago 05.07.2013, 12:28 GMT-4
Hi Nancy. I have the same error in a model with 3 species (modeled with the chemical engineering > electrokinetic flow module (chekf)) and 2 small electrodes (modeled whit the PDE module). After many tests changing the position on electrodes I concluded that the problem is related with the complexity of the resulting electric field that mobilizes the species. For some electrode's simple positions the model works, but from others it doesn't, and it's there when I get the Singulariry Error.

Let me know if you want to work together so maybe we can fix the problem.
Hi Nancy. I have the same error in a model with 3 species (modeled with the chemical engineering > electrokinetic flow module (chekf)) and 2 small electrodes (modeled whit the PDE module). After many tests changing the position on electrodes I concluded that the problem is related with the complexity of the resulting electric field that mobilizes the species. For some electrode's simple positions the model works, but from others it doesn't, and it's there when I get the Singulariry Error. Let me know if you want to work together so maybe we can fix the problem.
Marco Zanoni
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Posted: 1 decade ago 30.10.2013, 11:39 GMT-4
Hey Nancy,

I have the same problem.

Did you solve it?

Thanks.

Marco
Hey Nancy, I have the same problem. Did you solve it? Thanks. Marco
Nancy
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Posted: 1 decade ago 30.10.2013, 11:45 GMT-4
Hi,
I found that if you decrease the size of the meshing (go to extremely fine, then click on custom, and decrease the minimum size), it gets to work. Try with a lower dimension problem first, as it will solve faster.
Good luck!
Nancy
Hi, I found that if you decrease the size of the meshing (go to extremely fine, then click on custom, and decrease the minimum size), it gets to work. Try with a lower dimension problem first, as it will solve faster. Good luck! Nancy
Marco Zanoni
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Posted: 1 decade ago 30.10.2013, 13:17 GMT-4
Thanks Nancy.

It's working.

Marco
Thanks Nancy. It's working. Marco

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