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Calculate surface area in which a specified temperature limit is exceeded

Posted Jul 22, 2011, 6:16 a.m. EDT Heat Transfer & Phase Change, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.2 4 Replies

Sebastian Heß
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Hi,

I have calculated the time-dependent joule-heating of a structure, now I like to calculate the surface area in which a specified temperature limit is exceeded for each time step. Is there any possibility to do this in Comsol 4.2?

Thanks & best regards
Sebastian
4 Replies Last Post Jun 2, 2017, 10:26 a.m. EDT
John H.
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Posted: 1 decade ago Jul 22, 2011, 8:36 a.m. EDT
What you have to do is integrate a boolean expression such as T>50[degC] (which is 1 if true and 0 otherwise) over the domain of interest (that "surface" you speak of).

There are two ways to achieve this. Either you simply integrate the expression in post-processing (Results -> Derived Values). Or, slightly more complicated but offering more flexibility, you first define an integration operator for the domain (under the Model -> Defintions node) and then evaluate that operator using a Global Expression in post-processing.
What you have to do is integrate a boolean expression such as T>50[degC] (which is 1 if true and 0 otherwise) over the domain of interest (that "surface" you speak of). There are two ways to achieve this. Either you simply integrate the expression in post-processing (Results -> Derived Values). Or, slightly more complicated but offering more flexibility, you first define an integration operator for the domain (under the Model -> Defintions node) and then evaluate that operator using a Global Expression in post-processing.
Sebastian Heß
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Posted: 1 decade ago Jul 25, 2011, 4:25 a.m. EDT
Thanks John, you've helped me a lot :)
Thanks John, you've helped me a lot :)
Leonidas Asimakoulas
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Posted: 7 years ago Jun 2, 2017, 5:19 a.m. EDT
Updated: 7 years ago Jun 2, 2017, 5:34 a.m. EDT

What you have to do is integrate a boolean expression such as T>50[degC] (which is 1 if true and 0 otherwise) over the domain of interest (that "surface" you speak of).

There are two ways to achieve this. Either you simply integrate the expression in post-processing (Results -> Derived Values). Or, slightly more complicated but offering more flexibility, you first define an integration operator for the domain (under the Model -> Defintions node) and then evaluate that operator using a Global Expression in post-processing.


Hi,
Do you know by any change what will be the parameter to calculate this area? In my case I used:
if(T>Tvap, 2*dom,0) under the surface integral but the resulted area isn't what I would expected. Instead of dom what other variable is used for surface area calculation in Comsol 5.2a?
Thank you.

Edit:
I figured it out and it seems that the formula I used is right but please feel free to make any comments.
[QUOTE] What you have to do is integrate a boolean expression such as T>50[degC] (which is 1 if true and 0 otherwise) over the domain of interest (that "surface" you speak of). There are two ways to achieve this. Either you simply integrate the expression in post-processing (Results -> Derived Values). Or, slightly more complicated but offering more flexibility, you first define an integration operator for the domain (under the Model -> Defintions node) and then evaluate that operator using a Global Expression in post-processing. [/QUOTE] Hi, Do you know by any change what will be the parameter to calculate this area? In my case I used: if(T>Tvap, 2*dom,0) under the surface integral but the resulted area isn't what I would expected. Instead of dom what other variable is used for surface area calculation in Comsol 5.2a? Thank you. Edit: I figured it out and it seems that the formula I used is right but please feel free to make any comments.
Walter Frei COMSOL Employee

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Posted: 7 years ago Jun 2, 2017, 10:26 a.m. EDT
Hello,

You may also be interested in the timeint and timemax operators ( see section on Operators, Functions, and Constants in the COMSOL Multiphysics Reference Manual)

For example, you could plot:
timemax(0,30[s],T) which will show the maximum temperature that is achieved over the first 30 seconds.
or:
timeint(0,30[s],(T>400[K])) will compute and plot how long a particular region is held above 400K in the first 30 seconds.
Hello, You may also be interested in the timeint and timemax operators ( see section on Operators, Functions, and Constants in the COMSOL Multiphysics Reference Manual) For example, you could plot: timemax(0,30[s],T) which will show the maximum temperature that is achieved over the first 30 seconds. or: timeint(0,30[s],(T>400[K])) will compute and plot how long a particular region is held above 400K in the first 30 seconds.

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