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Weak Constraint thermal flux

Posted 16 mag 2013, 04:30 GMT-4 Structural Mechanics Version 4.3 4 Replies

Miroslav Repka
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Hi every body

I am using Weak form to model strongly coupled thermal-structural equations.My model consists of two layers.
I used Weak constraint to ensure that my thermal flux will be continuous but
Comsol gives me an error that "Expression must be linear in test function"..and i dont know how to solve it.
What does it mean?.Do I have to change a shape function?if yes,how can I do that

I used (q22-q2)*test(u3), where u3 is dependent variable for temperature and q variable for heat flux of each layer.

Coud you please help me?

Thank you



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4 Replies Last Post 16 mag 2013, 07:17 GMT-4
Mattia Montanari
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Posted: 1 decade ago 16 mag 2013, 05:48 GMT-4
Hi,

probably I misunderstand your question, but to make it clear: thermal heat flux is not constant among the elements!

In general, for Lagrange elements, the spatial derivatives of the principal variables (your case temperature,etc..) is not constant among two elements...

Mattia
Hi, probably I misunderstand your question, but to make it clear: thermal heat flux is not constant among the elements! In general, for Lagrange elements, the spatial derivatives of the principal variables (your case temperature,etc..) is not constant among two elements... Mattia
Miroslav Repka
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Posted: 1 decade ago 16 mag 2013, 06:18 GMT-4
Thank you for reply

yes you are right but thermal flux .I mean -lambda*gradT,must be continous from one layer to second ,no step change in interface boundary.
I am still facing this problem because my Weak constriant doesnt work.

I would be very glad If somebody could help me

Thank you
Thank you for reply yes you are right but thermal flux .I mean -lambda*gradT,must be continous from one layer to second ,no step change in interface boundary. I am still facing this problem because my Weak constriant doesnt work. I would be very glad If somebody could help me Thank you
Mattia Montanari
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Posted: 1 decade ago 16 mag 2013, 06:40 GMT-4
I cannot give you a solution, but gradT is the derivative of the temperature.. if your layers have boundaries defined on mesh ( as I guess it is ), your thermal flux cannot be continuous.
The reason is simple: with Lagrange elements you impose the continuity of the temperature among the elements, thus you cannot also ensure the continuity of the temperature derivatives.
I cannot give you a solution, but gradT is the derivative of the temperature.. if your layers have boundaries defined on mesh ( as I guess it is ), your thermal flux cannot be continuous. The reason is simple: with Lagrange elements you impose the continuity of the temperature among the elements, thus you cannot also ensure the continuity of the temperature derivatives.
Miroslav Repka
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Posted: 1 decade ago 16 mag 2013, 07:17 GMT-4
Thanks

Maybe I didnt express it clear for better understading what I mean I atteched a comparison with heat transfer modul(right flux).look at te shape of the curve.(values are different due to different geometry)
Thermal flux must be equal in the interface due to this fact I wanted to use Weak Constraint to prescribe
heat flux,but comsol gives me an error (mentioned above).

thank you

Miro
Thanks Maybe I didnt express it clear for better understading what I mean I atteched a comparison with heat transfer modul(right flux).look at te shape of the curve.(values are different due to different geometry) Thermal flux must be equal in the interface due to this fact I wanted to use Weak Constraint to prescribe heat flux,but comsol gives me an error (mentioned above). thank you Miro

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