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How does COMSOL take care of two heat-flux values assigned to the same boundary

Posted 27 giu 2012, 12:20 GMT-4 Version 4.2 3 Replies

Kapil Dev
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I built a simple model and added a heat-flux (Heat Flux1) with heat-transfer coefficient, h=5W/(m^2k) to all the boundaries for convective cooling. Then, I added another heat-flux (Heat Flux2) , wherein I assigned h=500 W/(m^2k) to one of the boundaries of my system. I was expecting that COMSOL will show an override on this boundary if I look into the list of boundaries in "Heat-Flux1". But, to my surprise, it does not.

What does COMSOL do internally? Based on my simulations, wherein I manually remove the boundary from previous heat-fluxes, the results are different in different cases. In other words, COMSOL is not doing an override automatically; it takes into account the previous heat-fluxes added to a boundary in some way.

Looking for your comments on this.

Thanks.
3 Replies Last Post 27 giu 2012, 14:41 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 giu 2012, 12:52 GMT-4
Hi

there are two behaviour of BCs: contributing (additive) or exclusive (one or the other but noh both) and incase of doubt, it's the one far down in the node tree that overirdes the one define previously (higher up).

This applies lso to physics so the order of these, in the node tree, has its importance, in particular ALE physics, check the doc

In this way you can overwrite most if not all default BCs that COMSOL proposes to give a well behaved solver condition start, by duplicating BC nodes later down.

This is explained in the COMSOl doc, and now in the new V4.3 we get finally a (more or less) complete list of these features, which over-ride, which contribute (also a more complete variable lists).

You will also see this on the small icon add-ons that appear when you add or move up and dovn in the node tree

--
Good luck
Ivar
Hi there are two behaviour of BCs: contributing (additive) or exclusive (one or the other but noh both) and incase of doubt, it's the one far down in the node tree that overirdes the one define previously (higher up). This applies lso to physics so the order of these, in the node tree, has its importance, in particular ALE physics, check the doc In this way you can overwrite most if not all default BCs that COMSOL proposes to give a well behaved solver condition start, by duplicating BC nodes later down. This is explained in the COMSOl doc, and now in the new V4.3 we get finally a (more or less) complete list of these features, which over-ride, which contribute (also a more complete variable lists). You will also see this on the small icon add-ons that appear when you add or move up and dovn in the node tree -- Good luck Ivar
Kapil Dev
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Posted: 1 decade ago 27 giu 2012, 14:22 GMT-4
Thanks for the answer, Ivar!

So, in my case, the heat-fluxes are additive.

Best,
Kapil
Thanks for the answer, Ivar! So, in my case, the heat-fluxes are additive. Best, Kapil
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 giu 2012, 14:41 GMT-4
Hi

I suppose so (would need to check the doc myself to be 100% sure ;). The COMSOl term is "contributing", take care, as it's rather important to understand the different terms, they are used rather systematically and are required to really understand the documentation. You can find a nice glossary here:

www.comsol.eu/products/multiphysics/glossary/

But I see nw that, as often, the example does not work, the terms are not in there ;)
should be just like entity, object, ... are also missing

My advice, run an indexer over your pdf documentation files and use that to search your documentation, things are often scattered around, but its in there somewhere ;)

check i.e. p435 COMSOLMultiphysicsUsersGuide.pdf v4.3 "Physics Exclusive and Contributing Feature Node Types"

--
Good luck
Ivar
Hi I suppose so (would need to check the doc myself to be 100% sure ;). The COMSOl term is "contributing", take care, as it's rather important to understand the different terms, they are used rather systematically and are required to really understand the documentation. You can find a nice glossary here: http://www.comsol.eu/products/multiphysics/glossary/ But I see nw that, as often, the example does not work, the terms are not in there ;) should be just like entity, object, ... are also missing My advice, run an indexer over your pdf documentation files and use that to search your documentation, things are often scattered around, but its in there somewhere ;) check i.e. p435 COMSOLMultiphysicsUsersGuide.pdf v4.3 "Physics Exclusive and Contributing Feature Node Types" -- Good luck Ivar

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