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"Time derivative only allowed with respect to mesh time." New error message in Comsol 4.2a

Posted Nov 2, 2011, 2:50 p.m. EDT Version 5.2a 14 Replies

Andrew Prudil Nuclear Materials
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Hi everyone,
I just upgraded to COMSOL 4.2a. When I try to run a model file which works in Comsol 4.2 I get a new error I can't seem to troubleshoot. "Time derivative only allowed with respect to mesh time." According to the error message it is in expression d(mod1.T,t). Which makes sense because T is my temperature and t is my time variable.

I tried searching but I have not encountered anyone else with the same error. Any ideas what this could mean? I've tried building a new solver tree, re meshing ect with no luck. Any suggestions would be great
14 Replies Last Post Jul 21, 2017, 7:55 a.m. EDT
Andrew Prudil Nuclear Materials
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Posted: 1 decade ago Nov 14, 2011, 4:50 p.m. EST
Hi everyone,
Just an update. I found a solution to this problem.

When using the d operator you cannot use 't'. In previous versions this was allowed. In the comsol user guide is now says to use "TIME" instead. For example d(T,t) is not allowed anymore. You must use d(T,TIME).
Hi everyone, Just an update. I found a solution to this problem. When using the d operator you cannot use 't'. In previous versions this was allowed. In the comsol user guide is now says to use "TIME" instead. For example d(T,t) is not allowed anymore. You must use d(T,TIME).
Yevgeniy Davletshin
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Posted: 1 decade ago Jan 7, 2013, 1:58 p.m. EST
Thanks for sharing.
Thanks for sharing.
Pedro Almeida
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Posted: 1 decade ago May 8, 2014, 10:28 a.m. EDT
Hi Andrew. This has been very helpful, thanks for sharing!

Hi Andrew. This has been very helpful, thanks for sharing!
Jing Huang
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Posted: 10 years ago Dec 17, 2014, 5:45 p.m. EST
Very helpful tip, thank you!
Very helpful tip, thank you!
Shivam Alakhramsing
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Posted: 10 years ago Apr 15, 2015, 8:15 a.m. EDT
Again, COMSOL riddles :) Thank you anyways!

Shivam
Again, COMSOL riddles :) Thank you anyways! Shivam
Jason Leung
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Posted: 9 years ago Sep 9, 2015, 1:10 a.m. EDT
Hey this is very helpful, also in Versions 5.1.
Thanks very much!!
Hey this is very helpful, also in Versions 5.1. Thanks very much!!
Xiangguo kong
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Posted: 9 years ago Nov 29, 2015, 10:01 p.m. EST
How do I use d(T,TIME) instead of d(T,t) ? In detail, where do I need to set? Thank you!
How do I use d(T,TIME) instead of d(T,t) ? In detail, where do I need to set? Thank you!
Xiangguo kong
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Posted: 9 years ago Nov 29, 2015, 10:06 p.m. EST
Hi, Dr. Huang, Do you know how to use d(p,TIME) instead of d(p,t). Thank you. This is my qq:845757859.
Hi, Dr. Huang, Do you know how to use d(p,TIME) instead of d(p,t). Thank you. This is my qq:845757859.
Andrew Prudil Nuclear Materials
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Posted: 9 years ago Nov 29, 2015, 10:42 p.m. EST
Hello Xiangguo Kong,

Where you make this change depends on your specific model. You want to find any place where d(p,t) occurs in the model. A good place to start is to search for d(p,t) by hitting ctrl+f in the model. Another option is to save the model as a java or matlab file so that you can search it for "d(p,t)".

I hope this helps,
Andrew
Hello Xiangguo Kong, Where you make this change depends on your specific model. You want to find any place where d(p,t) occurs in the model. A good place to start is to search for d(p,t) by hitting ctrl+f in the model. Another option is to save the model as a java or matlab file so that you can search it for "d(p,t)". I hope this helps, Andrew
Xiangguo kong
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Posted: 9 years ago Nov 30, 2015, 3:31 a.m. EST
Hello, Andrew Prudil,
Thank you for your reply. My model conatins Solid Mechanics and Darcy's Law. For solid Mechanics, we adopt stationary study. For Darcy's Law, we adopt Time-dependent study type. But when computeing Time-dependent study, it occurs "Time dervative only allowed with respect to mesh time, expression d(comp1.p,t)" . Save it as java or matlab file, we don't find d(comp1.p,t). Why? Do you have another method to solve it!
Thank you.
Hello, Andrew Prudil, Thank you for your reply. My model conatins Solid Mechanics and Darcy's Law. For solid Mechanics, we adopt stationary study. For Darcy's Law, we adopt Time-dependent study type. But when computeing Time-dependent study, it occurs "Time dervative only allowed with respect to mesh time, expression d(comp1.p,t)" . Save it as java or matlab file, we don't find d(comp1.p,t). Why? Do you have another method to solve it! Thank you.
Shayan Sombolestani
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Posted: 9 years ago Jan 21, 2016, 6:15 p.m. EST
Hello,
I have the same problem with Darcy's Law and Solid Mechanics. Did you find a way to solve this problem?
Thanks,
Hello, I have the same problem with Darcy's Law and Solid Mechanics. Did you find a way to solve this problem? Thanks,
Andrew Prudil Nuclear Materials
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Posted: 9 years ago Jan 22, 2016, 10:13 a.m. EST
Hello All,
If you were un able to find the source of the error it might be in one of the internal variables defined by comsol. You can see these under the 'equations' node if you have it enabled in the preferences. These equations are not searched using Control-F and are not output via when you save as MATLAB or JAVA files (so you would not have been able to find them).

I would suggest you take a moment to look through the equations nodes in both the solid-mechanics and the darcy's flow to see if you can find it in any of them. Otherwise I suggest contact Comsol support. Unfortunately I've never used that specific combination of physics modules, and thus never needed to fix this specific problem.

Best of luck,
Andrew
Hello All, If you were un able to find the source of the error it might be in one of the internal variables defined by comsol. You can see these under the 'equations' node if you have it enabled in the preferences. These equations are not searched using Control-F and are not output via when you save as MATLAB or JAVA files (so you would not have been able to find them). I would suggest you take a moment to look through the equations nodes in both the solid-mechanics and the darcy's flow to see if you can find it in any of them. Otherwise I suggest contact Comsol support. Unfortunately I've never used that specific combination of physics modules, and thus never needed to fix this specific problem. Best of luck, Andrew
Rune Ryberg Thygesen
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Posted: 8 years ago Oct 28, 2016, 5:00 a.m. EDT
Thanks!

Google "time derivative only allowed with respect to mesh time" got me here, and saved a lot of time!
Thanks! Google "time derivative only allowed with respect to mesh time" got me here, and saved a lot of time!
Rupak Bardhan Roy
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Posted: 7 years ago Jul 21, 2017, 7:55 a.m. EDT
This has been of great help. Thanks.
This has been of great help. Thanks.

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