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How I can appropriate / set a variable for temperature distribution on border?

Posted 26 sept. 2011, 03:51 UTC−4 Parameters, Variables, & Functions Version 4.2 4 Replies

Mikhail Polous
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Hello everybody!
I have already got a temperature field of the model. How I can appropriate / set a variable for temperature distribution on border?

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4 Replies Last Post 29 sept. 2011, 03:10 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26 sept. 2011, 07:09 UTC−4
Hi

the value you give is the value taken for eaxh mesh elements by COMSOL so if you give a function as variable ie. a T(z) and define this function via a Define Function ... then you will get a variable imposed temperature value depending on "z" (this applies to most variables and to all dimensions, COMSOL is fundamentally generalised)

--
Good luck
Ivar
Hi the value you give is the value taken for eaxh mesh elements by COMSOL so if you give a function as variable ie. a T(z) and define this function via a Define Function ... then you will get a variable imposed temperature value depending on "z" (this applies to most variables and to all dimensions, COMSOL is fundamentally generalised) -- Good luck Ivar
Mikhail Polous
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Posted: 1 decade ago 28 sept. 2011, 08:55 UTC−4
Thank you for quick response, Ivar.
But the thing is that I don’t have to define the function T(z), as it is unknown in the very beginning – it can be acquired only as a result of calculation. I have to assign a variable to the still uncalculated temperature distribution on the element boundary. And then I'd like to use this variable for another function in a section (definition --> function), which depends on it.

Here is an example from another physics field:
We have a diod (2 parallel plates). I need to define the current density as a function of potential distribution on the plate boundary (this potential is initially unknown, as it can be acquired only as a result of calculation, but the dependence of current density on the potential variable on the boundary is given). That is why I need to assign a variable (for example, 'v') to still uncalculated potential distribution on the plate boundary, so I can define a variable to current density j=f(v) in the section “definition->function”.

Do you have any ideas how to put this into life? I guess we should use “probe” here, but I don’t know how and if it’s going to work.
Thank you for quick response, Ivar. But the thing is that I don’t have to define the function T(z), as it is unknown in the very beginning – it can be acquired only as a result of calculation. I have to assign a variable to the still uncalculated temperature distribution on the element boundary. And then I'd like to use this variable for another function in a section (definition --> function), which depends on it. Here is an example from another physics field: We have a diod (2 parallel plates). I need to define the current density as a function of potential distribution on the plate boundary (this potential is initially unknown, as it can be acquired only as a result of calculation, but the dependence of current density on the potential variable on the boundary is given). That is why I need to assign a variable (for example, 'v') to still uncalculated potential distribution on the plate boundary, so I can define a variable to current density j=f(v) in the section “definition->function”. Do you have any ideas how to put this into life? I guess we should use “probe” here, but I don’t know how and if it’s going to work.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 28 sept. 2011, 14:49 UTC−4
Hi

A constant Temperature boundary is to allow COMSOL to calculate the heat flux through the boundary such that the temperature is as desired.

So, if you do not know the temperature, you must know something about the heat flux/exchange to allow COMSOL to estimate the Temperature

It's one ot the other,for me

--
Good luck
Ivar
Hi A constant Temperature boundary is to allow COMSOL to calculate the heat flux through the boundary such that the temperature is as desired. So, if you do not know the temperature, you must know something about the heat flux/exchange to allow COMSOL to estimate the Temperature It's one ot the other,for me -- Good luck Ivar
Mikhail Polous
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Posted: 1 decade ago 29 sept. 2011, 03:10 UTC−4
Hi, Ivar.
It is clear, that I need to know the value of T or flux/exchange on the boundary, but I have a vague situation over here: I know a flux that is dependent on the T at the boundary of the element... That is why at first I want to assign a variable to a still unknown T on the element boundary, and then to put flux by means of this variable. That is the thing I don't know how to do.. any ideas? :)
Hi, Ivar. It is clear, that I need to know the value of T or flux/exchange on the boundary, but I have a vague situation over here: I know a flux that is dependent on the T at the boundary of the element... That is why at first I want to assign a variable to a still unknown T on the element boundary, and then to put flux by means of this variable. That is the thing I don't know how to do.. any ideas? :)

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