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Error evaluating variable

Posted 11 apr 2015, 22:31 GMT-4 Version 4.2 4 Replies

Ernesto Leon
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Hello,

I am trying to model a heat transfer and mass diffusion process using the PDE module using the coefficient form and general form as function of "C" concentration and "T" temperature. However, keep getting the following error:

Failed to evaluate variable.
- Variable: u
- Geometry: 1
- Domain: 1

Failed to evaluate expression
- Expression: u
- Plot: surf1 (Surface)

I am rather new with COMSOL Multiphysics. Any guidance would be greatly appreciated.

Best regards.
4 Replies Last Post 17 apr 2015, 09:22 GMT-4
Lasse Murtomäki
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Posted: 9 years ago 13 apr 2015, 01:39 GMT-4
Hi

Your variables are C and T, there is no u. Look at the equations of your physics. Change the plotting variable.

Your global equations have variables vt and wt. What are they? I did not find them defined anywhere.

br
Lasse
Hi Your variables are C and T, there is no u. Look at the equations of your physics. Change the plotting variable. Your global equations have variables vt and wt. What are they? I did not find them defined anywhere. br Lasse
Ernesto Leon
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Posted: 9 years ago 14 apr 2015, 01:03 GMT-4

Hi,

I don't understand why it is looking for "u" if there is not "u" either. How do I change the plotting variable?

vt and wt are the accumulated heat and mass as function of time respectively.

Regards,
Ernesto


Hi

Your variables are C and T, there is no u. Look at the equations of your physics. Change the plotting variable.

Your global equations have variables vt and wt. What are they? I did not find them defined anywhere.

br
Lasse


Hi, I don't understand why it is looking for "u" if there is not "u" either. How do I change the plotting variable? vt and wt are the accumulated heat and mass as function of time respectively. Regards, Ernesto [QUOTE] Hi Your variables are C and T, there is no u. Look at the equations of your physics. Change the plotting variable. Your global equations have variables vt and wt. What are they? I did not find them defined anywhere. br Lasse [/QUOTE]
Lasse Murtomäki
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Posted: 9 years ago 14 apr 2015, 01:22 GMT-4
Hi

Just type T or C in the box where the variable to be plotted is defined. Usually in the PDE node "u" is the generic variable name. Why you have C and T beats me, an earlier Comsol version?

I do not see variables vt or wt defined anywhere, neither v or w (vt and wt would then be their time derivatives). Your Intop1 and Intop2 are identical.

br
Lasse
Hi Just type T or C in the box where the variable to be plotted is defined. Usually in the PDE node "u" is the generic variable name. Why you have C and T beats me, an earlier Comsol version? I do not see variables vt or wt defined anywhere, neither v or w (vt and wt would then be their time derivatives). Your Intop1 and Intop2 are identical. br Lasse
Ernesto Leon
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Posted: 9 years ago 17 apr 2015, 09:22 GMT-4
Hello,

I am using COMSOL 4.2. I added the parameters "u" and "u2" under the global parameter definition and it solved the problem.

Thank you very much for your advice.

Best regards,
Hello, I am using COMSOL 4.2. I added the parameters "u" and "u2" under the global parameter definition and it solved the problem. Thank you very much for your advice. Best regards,

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