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Evaluate variable for a specific time during solving

Posted Feb 29, 2012, 10:23 a.m. EST Heat Transfer & Phase Change, Parameters, Variables, & Functions, Studies & Solvers Version 4.2 7 Replies

Alexander Malzkuhn
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Hello everybody,

I had an idea this morning, but I could not find anything in the documentation, that this would be possible. Is it possible to store the value of a specific time during solving into another variable, that does not change for the further solving process, e. g. to simulate the thermal strain of a material, that is heaten until a certain time and then cools down? At the end of the heating phase, I want to evaluate the temperature to become it the new reference temperature for my material.
I thought, this could be a workaround for my plasticity problem: www.comsol.de/community/forums/general/thread/26467/ In that model I use two study steps with two different heat transfer modules. The second one uses the temperature distribution at the end of the heating phase of the first one as initial values and then it is used as new reference temperature for the thermal strain, but that way always something goes wrong with the plasticity variables. If I was able to store the new reference temperature in a new variable and put everything in one study step, it could be a solution for the initial strain value problem, I think.
7 Replies Last Post Mar 1, 2012, 3:01 p.m. EST
Jaap Verheggen
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Posted: 1 decade ago Feb 29, 2012, 10:32 a.m. EST
Check table 3-3 in the Comsol multiphysics users guide, operators such as 'at', 'with' and 'prev'. should help you with what you want.

-Jaap
Check table 3-3 in the Comsol multiphysics users guide, operators such as 'at', 'with' and 'prev'. should help you with what you want. -Jaap
Alexander Malzkuhn
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Posted: 1 decade ago Feb 29, 2012, 10:37 a.m. EST
I read that chapter of the user's guide, but there was mentioned that those operators could only be used during the results evaluation and not for model setup and that the prev operator would only work for the time-discret solver. That is why I am asking, if there is a trick or something.
I read that chapter of the user's guide, but there was mentioned that those operators could only be used during the results evaluation and not for model setup and that the prev operator would only work for the time-discret solver. That is why I am asking, if there is a trick or something.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 29, 2012, 11:18 a.m. EST
Hi

i have also understood that those are to be used during postprocessing, as a few others. for time derivatives one need to define a new global equation and variable see the KB (Knowledge Base

--
Good luck
Ivar
Hi i have also understood that those are to be used during postprocessing, as a few others. for time derivatives one need to define a new global equation and variable see the KB (Knowledge Base -- Good luck Ivar
Alexander Malzkuhn
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Posted: 1 decade ago Feb 29, 2012, 11:26 a.m. EST
Thanks for your reply, but I just don't understand what you mean. :-)
Thanks for your reply, but I just don't understand what you mean. :-)
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 29, 2012, 1:32 p.m. EST
Hi

I understand, te web ate up the end of my answer ;)

I was thinking of methods based on
www.comsol.eu/support/knowledgebase/913/
www.comsol.eu/support/knowledgebase/1101/
+ one more that I couldn t find back

Then to constrain this new variable in its equation.

But I might have missed your problem ;)

If you are looking for ways in stationary to prestress material w.r.t. different temperatures, based on their respective theal expansion, you can also play with the Linear material node "zero strain temperature" for the different materials.

--
Good luck
Ivar
Hi I understand, te web ate up the end of my answer ;) I was thinking of methods based on http://www.comsol.eu/support/knowledgebase/913/ http://www.comsol.eu/support/knowledgebase/1101/ + one more that I couldn t find back Then to constrain this new variable in its equation. But I might have missed your problem ;) If you are looking for ways in stationary to prestress material w.r.t. different temperatures, based on their respective theal expansion, you can also play with the Linear material node "zero strain temperature" for the different materials. -- Good luck Ivar
Alexander Malzkuhn
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Posted: 1 decade ago Feb 29, 2012, 4:41 p.m. EST
Thanks, but that is not what I'm looking for. Let's say, I solve a time dependent problem for 10 seconds. For the last 6 seconds I want to do time dependent computations, that depend on a variable value of t = 4s. I think it is not that easy like "T(4s)".
Thanks, but that is not what I'm looking for. Let's say, I solve a time dependent problem for 10 seconds. For the last 6 seconds I want to do time dependent computations, that depend on a variable value of t = 4s. I think it is not that easy like "T(4s)".
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 1, 2012, 3:01 p.m. EST
Hi

in v4.2a you have the prev() operator, but it does not count in "time" but in steps w.r.t current. See UsersGuide 4.2a p119. Also search for special operators

But I have never used it myself

--
Good luck
Ivar
Hi in v4.2a you have the prev() operator, but it does not count in "time" but in steps w.r.t current. See UsersGuide 4.2a p119. Also search for special operators But I have never used it myself -- Good luck Ivar

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