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Solving PDE's on simple geomtry
Posted Feb 7, 2011, 3:55 a.m. EST 3 Replies
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Hi.
I have recently started "playing" with the PDE possibilities in COMSOL and are currently testing a bit using them in connection to heat transfer. Still I want to do some calculations on simple geomtries and without any other physics involved. This is purely to check if my PDE's is correctly deduced.
I have a simple geometry and a PDE describing a chemical reaction in that geometry with T as the only variable parameter.
I want to control T in my geometry as a function of time and has done so with an interpolation function and defined that the PDE is valid in my entire geometry.
When trying to solve I get the error message that I have not defined T in my geometry.
Tried to read a bit in the 4.1 MulitUsers Guide and have looked at some models from the Model Exchange, but failed to find any solution, but as I understand this should be a simple task.
Any tips on how to do this, or if anyone knows of an exact artice describing how to set up such a simple model, my day would be saved.
Thanks
Nils Eivind
I have recently started "playing" with the PDE possibilities in COMSOL and are currently testing a bit using them in connection to heat transfer. Still I want to do some calculations on simple geomtries and without any other physics involved. This is purely to check if my PDE's is correctly deduced.
I have a simple geometry and a PDE describing a chemical reaction in that geometry with T as the only variable parameter.
I want to control T in my geometry as a function of time and has done so with an interpolation function and defined that the PDE is valid in my entire geometry.
When trying to solve I get the error message that I have not defined T in my geometry.
Tried to read a bit in the 4.1 MulitUsers Guide and have looked at some models from the Model Exchange, but failed to find any solution, but as I understand this should be a simple task.
Any tips on how to do this, or if anyone knows of an exact artice describing how to set up such a simple model, my day would be saved.
Thanks
Nils Eivind
3 Replies Last Post Feb 7, 2011, 6:42 a.m. EST
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Posted:
1 decade ago
Hi,
if I understood, you don't have problems setting up your own PDE, the problem is giving an input prescription? I mean: T(x,t) is an independent variable in your model because your (material or reaction) coefficients depend on T?
In that case you should check, if your are really having problems with that:
set up a new simple PDE (coefficients are zero or 1 - no connection to T). No complicated things. Then solve and check your defined varaiable T if it is defined. That would be my starting point.
At least, how did you define your "T"-function? Maybe the problem is caused by this?
best regards
if I understood, you don't have problems setting up your own PDE, the problem is giving an input prescription? I mean: T(x,t) is an independent variable in your model because your (material or reaction) coefficients depend on T?
In that case you should check, if your are really having problems with that:
set up a new simple PDE (coefficients are zero or 1 - no connection to T). No complicated things. Then solve and check your defined varaiable T if it is defined. That would be my starting point.
At least, how did you define your "T"-function? Maybe the problem is caused by this?
best regards
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Posted:
1 decade ago
Hi
I'm also thinking of the material T and p pressure dependence, that might play you a trick.
My advise is always: start with user defined materials, with constant material properties, then used the advanced (often non-linear) material properties
--
Good luck
Ivar
I'm also thinking of the material T and p pressure dependence, that might play you a trick.
My advise is always: start with user defined materials, with constant material properties, then used the advanced (often non-linear) material properties
--
Good luck
Ivar
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Posted:
1 decade ago
Thanks guys.
Testing with only constant vaules with success first so the PDE works fine.
Figured out what was wrong, after some tidious reading there was one occurence of T and not T(t) in the PDE equation, giving the missing definition of T.
Got a good correlation between COMSOL and the other reference calculations so I'm considering this one "a wrap"
NE
Testing with only constant vaules with success first so the PDE works fine.
Figured out what was wrong, after some tidious reading there was one occurence of T and not T(t) in the PDE equation, giving the missing definition of T.
Got a good correlation between COMSOL and the other reference calculations so I'm considering this one "a wrap"
NE