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Volume integration

Posted 23.11.2009, 17:06 GMT-5 3 Replies

Johan Gustafsson
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Hi,

I am a COMSOL-beginner with what I guess might be a quite basic question. How (if possible) can I use Subdomain Integration Variables to get the volume of a subdomain in 2D axisymmetry mode. I need to set the density of a domain from the mass.

Thanks,
Johan
3 Replies Last Post 18.12.2009, 06:14 GMT-5
Michael Hochman
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Posted: 1 decade ago 23.11.2009, 19:32 GMT-5
An easy way would just be to define a subdomain integration coupling variable, name it "volume," and use 1 as your expression. Now your volume variable will contain the actual volume of that subdomain. I just tried this method for a simple rectangular geometry and it seems to work fine.

I should point out that I tried this with plane-strain mode, I'm not sure if you need to do anything differently for axisymmetric mode. But you can easily try it with simple geometry (that you know the answer to) and see if it works.

Good luck,

Mike
An easy way would just be to define a subdomain integration coupling variable, name it "volume," and use 1 as your expression. Now your volume variable will contain the actual volume of that subdomain. I just tried this method for a simple rectangular geometry and it seems to work fine. I should point out that I tried this with plane-strain mode, I'm not sure if you need to do anything differently for axisymmetric mode. But you can easily try it with simple geometry (that you know the answer to) and see if it works. Good luck, Mike
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27.11.2009, 17:55 GMT-5
Hi

for axisymmetry you must use the "2*pi*r" with some care, it can be applied by a click for the BC (boundary conditions since 3.5) but must be applied by "hand" for boundary integration variables.

As suggested, by trying out on simple cases, and studying the units of COMSOL you can find easily the correct dimensions to apply (always check units 30 years later I start to understand that statement from my physics teacher ;)

COMSOL requires some "thinking" and pysics knowledge, but it has far more freedom than other "out-of the box" FEM programmes.

Good luck
Ivar
Hi for axisymmetry you must use the "2*pi*r" with some care, it can be applied by a click for the BC (boundary conditions since 3.5) but must be applied by "hand" for boundary integration variables. As suggested, by trying out on simple cases, and studying the units of COMSOL you can find easily the correct dimensions to apply (always check units 30 years later I start to understand that statement from my physics teacher ;) COMSOL requires some "thinking" and pysics knowledge, but it has far more freedom than other "out-of the box" FEM programmes. Good luck Ivar
Johan Gustafsson
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Posted: 1 decade ago 18.12.2009, 06:14 GMT-5
Thanks! Works great!

Regards,
Johan
Thanks! Works great! Regards, Johan

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