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Temperatures calculated but thermal expansion calculation is missing ?

Posted Jan 17, 2014, 2:30 p.m. EST General, Heat Transfer & Phase Change, Structural Mechanics Version 4.4, Version 5.2 15 Replies

Hans Gennerich
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I generate a quite simple 3-D model:
A cylinder made of copper with a radius of 0.2m and a height of 0.5m and heated at its mantle with a total energy of 1000 Watts for one hour. Within this cylinder included in the center, there is another cylinder made of titanium with a radius of 0.1m and a length of 0.3m.

I apply the physics:
- Heat transfer in solids and
- solid mechanics

A "Multiphysics" node is generated automaticely.
I choose "temperature coupling"

I generate a normal sized mesh and calculate
a time dependend study with 10 sec steps for one hour.

I get a reasonal temperature distribution from the calculation.
But I'm surpised, that the elastic strain energy density (solid.Ws (J/m^3)) and all other parameters like (solid.ep1) of the solid mechanics are exactly zero, without any decimals. As there is a temperature difference of 5K and the thermal expansion coefficients of the material differ by 10 exp(-5) I would expect some stress.

My impression is, there is no mechanics calculated.

Any ideas, what I might have missed?

15 Replies Last Post May 23, 2016, 11:14 a.m. EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 1 decade ago Jan 20, 2014, 2:07 a.m. EST
Hi,

In addition to the Temperature Coupling node under Multiphysics, you need a Thermal Expansion node.

Regards,
Henrik
Hi, In addition to the Temperature Coupling node under Multiphysics, you need a Thermal Expansion node. Regards, Henrik
Hans Gennerich
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Posted: 1 decade ago Jan 20, 2014, 5:09 a.m. EST
Thank You for this hint!

But there is no "Thermal Expansion" node available, as far as I see.
Where can I find it?

Under the "Multiphysics"-node there is only "Temperature Coupling" listed.
Is it only available with additional modules ?

Thank You for this hint! But there is no "Thermal Expansion" node available, as far as I see. Where can I find it? Under the "Multiphysics"-node there is only "Temperature Coupling" listed. Is it only available with additional modules ?
Henrik Sönnerlind COMSOL Employee

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Posted: 1 decade ago Jan 20, 2014, 6:55 a.m. EST
Yes, it requires the Structural Mechanics or MEMS modules.

Regards,
Henrik
Yes, it requires the Structural Mechanics or MEMS modules. Regards, Henrik
Hans Gennerich
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Posted: 1 decade ago Jan 21, 2014, 4:53 a.m. EST
Thank You; Yes it is available since I installed the Structural Mechanics module.

I find it surprising, that the reaction of COMSOL to the not installed feature is to calculate zeroes instead of giving a hint, that the calculation of thermal expansion needs an additional module.
Thank You; Yes it is available since I installed the Structural Mechanics module. I find it surprising, that the reaction of COMSOL to the not installed feature is to calculate zeroes instead of giving a hint, that the calculation of thermal expansion needs an additional module.
Suresh Seetharam
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Posted: 1 decade ago Jan 21, 2014, 5:20 a.m. EST
Hi,



But I guess you may already know that you can introduce thermal expansion yourself into the basic mechanics node. I had done this long time ago, see the following thread.

www.comsol.com/community/forums/general/thread/39909

Of course, you do not have to do it the same way, it can also be introduced via the initial stress node as Henrik suggested quite recently.



Suresh
Hi, But I guess you may already know that you can introduce thermal expansion yourself into the basic mechanics node. I had done this long time ago, see the following thread. http://www.comsol.com/community/forums/general/thread/39909 Of course, you do not have to do it the same way, it can also be introduced via the initial stress node as Henrik suggested quite recently. Suresh
Julien Givernaud
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Posted: 1 decade ago Jan 21, 2014, 5:28 a.m. EST
Hello,

I try your hint Suresh but it doesn't work. Are you sure that it could works?
Can you show us a simple example of this implementation via the default structural mechanics physic?

Best regards

Julien
Hello, I try your hint Suresh but it doesn't work. Are you sure that it could works? Can you show us a simple example of this implementation via the default structural mechanics physic? Best regards Julien
Henrik Sönnerlind COMSOL Employee

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Posted: 1 decade ago Jan 21, 2014, 7:20 a.m. EST

Thank You; Yes it is available since I installed the Structural Mechanics module.

I find it surprising, that the reaction of COMSOL to the not installed feature is to calculate zeroes instead of giving a hint, that the calculation of thermal expansion needs an additional module.


Actually, what you did is nothing wrong per se (with or without the Structural Mechanics module); you fed the temperatures to the Solid Mechanics interface, so that any temperature dependent data (like material properties) would receive this temperature. There is no way the software could foresee whether you actually wanted only this or if you also wanted a thermal expansion to occur.

Regards,
Henrik
[QUOTE] Thank You; Yes it is available since I installed the Structural Mechanics module. I find it surprising, that the reaction of COMSOL to the not installed feature is to calculate zeroes instead of giving a hint, that the calculation of thermal expansion needs an additional module. [/QUOTE] Actually, what you did is nothing wrong per se (with or without the Structural Mechanics module); you fed the temperatures to the Solid Mechanics interface, so that any temperature dependent data (like material properties) would receive this temperature. There is no way the software could foresee whether you actually wanted only this or if you also wanted a thermal expansion to occur. Regards, Henrik
Hans Gennerich
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Posted: 1 decade ago Jan 21, 2014, 7:34 a.m. EST
I thought the software might have been aware of that, as I asked for strain, stress and dislocations which all were calculated to be zero without thermal expansions. I did not expect that a separate module was needed to offer me the coupling between mechanics and heat as both physics were basically integrated in the basic module. At this point a signal at the multiphysics node would have been helpfull, telling me, calculation of thermal expansion is only available after installing the structural mechanics module.

I'm still not confident enough with the philosophy of COMSOL, to foresee this myself.

Thank You
I thought the software might have been aware of that, as I asked for strain, stress and dislocations which all were calculated to be zero without thermal expansions. I did not expect that a separate module was needed to offer me the coupling between mechanics and heat as both physics were basically integrated in the basic module. At this point a signal at the multiphysics node would have been helpfull, telling me, calculation of thermal expansion is only available after installing the structural mechanics module. I'm still not confident enough with the philosophy of COMSOL, to foresee this myself. Thank You
Julien Givernaud
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Posted: 1 decade ago Jan 23, 2014, 8:17 a.m. EST
Hello,

Someone can confirm Sureh hint for the implement of the thermal expansion in the standard mechanical module by coupling with heat transfert module?

Best regards

Julien
Hello, Someone can confirm Sureh hint for the implement of the thermal expansion in the standard mechanical module by coupling with heat transfert module? Best regards Julien
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Jan 23, 2014, 9:16 a.m. EST
Hi Julien,

Yes you can implement thermal expansion following the instruction in the thread Suresh pointed to.

Nagi Elabbasi
Veryst Engineering
Hi Julien, Yes you can implement thermal expansion following the instruction in the thread Suresh pointed to. Nagi Elabbasi Veryst Engineering
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Jan 23, 2014, 9:32 a.m. EST
One way to find out whether COMSOL is using thermal expansion or any other property/feature (beside examining the results) is to go to the material node and check which properties are actually used in the analysis (look for the check mark to the left of the list of properties). In your case, the thermal expansion coefficient should not be marked.

In general though the burden is on the user not the software tool (COMSOL or otherwise) to make sure their model is a good representation of their physical problem in terms of physics, material models, loads, etc.

Nagi Elabbasi
Veryst Engineering
One way to find out whether COMSOL is using thermal expansion or any other property/feature (beside examining the results) is to go to the material node and check which properties are actually used in the analysis (look for the check mark to the left of the list of properties). In your case, the thermal expansion coefficient should not be marked. In general though the burden is on the user not the software tool (COMSOL or otherwise) to make sure their model is a good representation of their physical problem in terms of physics, material models, loads, etc. Nagi Elabbasi Veryst Engineering
Julien Givernaud
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Posted: 1 decade ago Jan 23, 2014, 11:26 a.m. EST
Thank you,

I think it works!!
Thank you, I think it works!!
Julien Givernaud
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Posted: 1 decade ago Jan 24, 2014, 3:34 a.m. EST
Hello,

I join a very simple model with the defalut solid mechanic physic in which I have implement the thermal expansion.
Can someone (who have the right Comsol model with thermal expansion included) compare with my results?

Thank you very

Julien
Hello, I join a very simple model with the defalut solid mechanic physic in which I have implement the thermal expansion. Can someone (who have the right Comsol model with thermal expansion included) compare with my results? Thank you very Julien
Julien Givernaud
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Posted: 1 decade ago Jan 28, 2014, 9:28 a.m. EST
Hello,

For information, the hint work but results are more accurate with the addition of:
-1.65*alpha[1/K]*(T-Tref)*bulkmodulus
instead of
-3*alpha[1/K]*(T-Tref)*bulkmodulus

in the end of solid.Sl11, 22, 33


best regards
Hello, For information, the hint work but results are more accurate with the addition of: -1.65*alpha[1/K]*(T-Tref)*bulkmodulus instead of -3*alpha[1/K]*(T-Tref)*bulkmodulus in the end of solid.Sl11, 22, 33 best regards
Patrick Morse
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Posted: 9 years ago May 23, 2016, 11:14 a.m. EDT
What is the 1.65 multiplication factor for? I understand the rest of the equation just not the added multiplication factor. Another note, you can change the initial sign from negative to positive if you switch T and T0.
What is the 1.65 multiplication factor for? I understand the rest of the equation just not the added multiplication factor. Another note, you can change the initial sign from negative to positive if you switch T and T0.

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