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Undefined value found for fluid transport with heat transfer
Posted May 27, 2011, 3:43 p.m. EDT Version 4.1, Version 4.2a 5 Replies
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Hi,
I am solving a coupled problem with a energy equation using heat transfer in solids, a fluid mass transport equation with the transport in diluted species, and a vapor mass transport equation using the user defined PDE. The other equation is a Darcy's law to find the total pressure.
I am getting the following error:
Repeated error test failures. May have reached a singularity.
Time : 9.453450314751982e-005
Undefined value found.
Undefined value found in the stiffness matrix.
There are 6 equations giving NaN/Inf in the matrix rows for the variable mod1.c v
at coordinates: (0.0173581,0.00710536), (0.0175,0.00701763), (0.017429,0.00706149), (0.0175,0.00710536), (0.017429,0.00714922), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns
Last time step is not converged.
I have checked the equations, BCs many times and still have no idea what I could do about it. Could you please give me any suggestions?
Thanks a million~~
I am solving a coupled problem with a energy equation using heat transfer in solids, a fluid mass transport equation with the transport in diluted species, and a vapor mass transport equation using the user defined PDE. The other equation is a Darcy's law to find the total pressure.
I am getting the following error:
Repeated error test failures. May have reached a singularity.
Time : 9.453450314751982e-005
Undefined value found.
Undefined value found in the stiffness matrix.
There are 6 equations giving NaN/Inf in the matrix rows for the variable mod1.c v
at coordinates: (0.0173581,0.00710536), (0.0175,0.00701763), (0.017429,0.00706149), (0.0175,0.00710536), (0.017429,0.00714922), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns
Last time step is not converged.
I have checked the equations, BCs many times and still have no idea what I could do about it. Could you please give me any suggestions?
Thanks a million~~
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5 Replies Last Post Sep 6, 2012, 10:50 a.m. EDT
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Posted:
1 decade ago
Hi
have you check that you initial conditions are OK ? hit the "Study ... Dependent variables", right-click "Compute to Selected" anc check the coherence of all initial values
What puzzles me is that your mod1_P_g is flagged Solved for this field "UNCHECKED", and it's greyed, so COMSOL is not accepting to solve for all physics, this could lead to NaNs, but why ?
Have you tried to use a segregated solver, rather than the direct one. Your model is too complex for me to "take it in 5 min" my ususal time limit here on the Forum ;) (My boss have given me many studies for today too )
This was as seen from v4.2 (I have uninstalled the older ones)
--
Good luck
Ivar
have you check that you initial conditions are OK ? hit the "Study ... Dependent variables", right-click "Compute to Selected" anc check the coherence of all initial values
What puzzles me is that your mod1_P_g is flagged Solved for this field "UNCHECKED", and it's greyed, so COMSOL is not accepting to solve for all physics, this could lead to NaNs, but why ?
Have you tried to use a segregated solver, rather than the direct one. Your model is too complex for me to "take it in 5 min" my ususal time limit here on the Forum ;) (My boss have given me many studies for today too )
This was as seen from v4.2 (I have uninstalled the older ones)
--
Good luck
Ivar
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Posted:
1 decade ago
Hi Ivar,
Thank you so much for your time and suggestions.
I took a look at the initial values and the mod1.P_g has zeros everywhere initially, which does not make sense. I have specified it to be the atmospheric pressure. Do you know why and how I could modify this?
"What puzzles me is that your mod1_P_g is flagged Solved for this field "UNCHECKED", and it's greyed, so COMSOL is not accepting to solve for all physics, this could lead to NaNs, but why ?"
--I don't quite get this. Could you please explain a little bit? Thank you so much!
I will check out segregated solvers.
Thanks a lot again. Really appreciate it.
Haolin
Thank you so much for your time and suggestions.
I took a look at the initial values and the mod1.P_g has zeros everywhere initially, which does not make sense. I have specified it to be the atmospheric pressure. Do you know why and how I could modify this?
"What puzzles me is that your mod1_P_g is flagged Solved for this field "UNCHECKED", and it's greyed, so COMSOL is not accepting to solve for all physics, this could lead to NaNs, but why ?"
--I don't quite get this. Could you please explain a little bit? Thank you so much!
I will check out segregated solvers.
Thanks a lot again. Really appreciate it.
Haolin
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Posted:
1 decade ago
Hi Ivar,
And when I used the segregated solver, another error was given:
Recoverable error in residual, but solver could not recover.
Time : 0.0005509748135944119
Last time step is not converged.
I searched this forum and online but had no luck what this means.....
Your help is greatly appreciated.
Best,
Haolin
And when I used the segregated solver, another error was given:
Recoverable error in residual, but solver could not recover.
Time : 0.0005509748135944119
Last time step is not converged.
I searched this forum and online but had no luck what this means.....
Your help is greatly appreciated.
Best,
Haolin
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Posted:
1 decade ago
Hi
for me it remains linked to an "ill conditioned matrix" = BCs that are not sufficiently independent or missing or initial values too far off from expected results.
Perhaps you can start with the model somewhat simplified, run a first time, use the results as initial conditions, or as a linear interpolation of the initial conditions. With pressure ayou have also the relative "gauge" pressure and the absolute pressure" thta might play you a game. Finally many of the material properties are T and p dependent, which makes the simulations non-linear, even if they are often just as "correct" if you used constant values for the material properties
--
Good luck
Ivar
for me it remains linked to an "ill conditioned matrix" = BCs that are not sufficiently independent or missing or initial values too far off from expected results.
Perhaps you can start with the model somewhat simplified, run a first time, use the results as initial conditions, or as a linear interpolation of the initial conditions. With pressure ayou have also the relative "gauge" pressure and the absolute pressure" thta might play you a game. Finally many of the material properties are T and p dependent, which makes the simulations non-linear, even if they are often just as "correct" if you used constant values for the material properties
--
Good luck
Ivar
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Posted:
1 decade ago
Hi,
Was this issue solved? I have downloaded the model you put here to try and learn from it. If you have one, can you contact me and send me the model? I'm having trouble with coupling physics in *my* model.
My E-mail is Shovalwarman@gmail.com
thank you very much,
Shoval
Was this issue solved? I have downloaded the model you put here to try and learn from it. If you have one, can you contact me and send me the model? I'm having trouble with coupling physics in *my* model.
My E-mail is Shovalwarman@gmail.com
thank you very much,
Shoval