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Periodic boundary condition

Posted 24 janv. 2012, 14:56 UTC−5 Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.3a 6 Replies

Melanie Pigeon
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Can the periodic boundary condition be applied to a transient model (laminar flow equation).

I have a fairly complex geometry which has a repeated pattern. I am hoping that I can use a small subset of it and use the periodic boundary condition in the transient state to find the solution rather than using the complete model which would have way too many DOFs.

Is this possible? How do I implement this?

Note that this model consists of a pipe with a perforation
6 Replies Last Post 9 mai 2013, 10:50 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 25 janv. 2012, 16:51 UTC−5
Hi

you have two Pair conditions, I see in SPF: Wall or Flow continuity (you must first define your identity pair to get the internal mapping set up.

Any other condition you must define yourself via weak conditions (if possible, but as many things are possible in COMSOL why not try)

--
Good luck
Ivar
Hi you have two Pair conditions, I see in SPF: Wall or Flow continuity (you must first define your identity pair to get the internal mapping set up. Any other condition you must define yourself via weak conditions (if possible, but as many things are possible in COMSOL why not try) -- Good luck Ivar
Melanie Pigeon
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Posted: 1 decade ago 29 janv. 2012, 15:40 UTC−5
How exactly do I set up this flow continuity? Can I solve first at SS and use the flow continuity for transient? Or is there anyway to simultaneously set the initial flow rate in the inlet for the first time frame then let it use the flow continuity from the outlet to determine the inlet?
How exactly do I set up this flow continuity? Can I solve first at SS and use the flow continuity for transient? Or is there anyway to simultaneously set the initial flow rate in the inlet for the first time frame then let it use the flow continuity from the outlet to determine the inlet?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 29 janv. 2012, 16:29 UTC−5
Hi

interesting question. I'm not sure I catch 100% your model, but from what I read you want an inlet-outlet pair, probably only for the flow velocity and for the pressure, perhaps something like outlet = inlet + some pressure drop.

In many cases one can do a SS study first and use the results as base for a separate study regarding other variables (provided one can accept the approximation that they are fuly decoupled), this will solve in a faster way and with less ram. If not one need a segregated solver and alternate between the U,p and the other variables. As a dirct solving might not work due to the all the non linear couplings (but this is probably model dependent).

Not evident to say like that "in all generality" but why not try with a identity pair on the velocity and a 0 pressure outlet (if no gravity body load is used) and use that as starting point for the other variable solving. The resluting inlet pressure would then be the pressure drop to consider (per pair)

Maybe someone else has done it already (I havent ;) so consider it as a first guess

--
Good luck
Ivar
Hi interesting question. I'm not sure I catch 100% your model, but from what I read you want an inlet-outlet pair, probably only for the flow velocity and for the pressure, perhaps something like outlet = inlet + some pressure drop. In many cases one can do a SS study first and use the results as base for a separate study regarding other variables (provided one can accept the approximation that they are fuly decoupled), this will solve in a faster way and with less ram. If not one need a segregated solver and alternate between the U,p and the other variables. As a dirct solving might not work due to the all the non linear couplings (but this is probably model dependent). Not evident to say like that "in all generality" but why not try with a identity pair on the velocity and a 0 pressure outlet (if no gravity body load is used) and use that as starting point for the other variable solving. The resluting inlet pressure would then be the pressure drop to consider (per pair) Maybe someone else has done it already (I havent ;) so consider it as a first guess -- Good luck Ivar
Melanie Pigeon
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Posted: 1 decade ago 29 janv. 2012, 17:15 UTC−5
Essentially I want to cut down on my model size (and RAM). I have a repeated pattern for the coil (coil+holes). I was hoping I could solve for a smaller subset repeatedly. I therefore want to know if this fluid continuity feature can be used to pair the outlet and the inlet
Essentially I want to cut down on my model size (and RAM). I have a repeated pattern for the coil (coil+holes). I was hoping I could solve for a smaller subset repeatedly. I therefore want to know if this fluid continuity feature can be used to pair the outlet and the inlet
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 30 janv. 2012, 01:35 UTC−5
Hi

I havent tried it, so the easiest is to take a long tube, chop it up and compare the results

--
Good luck
Ivar
Hi I havent tried it, so the easiest is to take a long tube, chop it up and compare the results -- Good luck Ivar
Francesca Messina
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Posted: 1 decade ago 9 mai 2013, 10:50 UTC−4
Dear Melanie,

Can I ask you how do you solve the problem?

I have a problem like yours, with a periodicity in my domain, so I would like to simulate only a part of it using periodic flow conditions, but I have some troubles...

Thanks a lot.

Best Regards,

Francesca
Dear Melanie, Can I ask you how do you solve the problem? I have a problem like yours, with a periodicity in my domain, so I would like to simulate only a part of it using periodic flow conditions, but I have some troubles... Thanks a lot. Best Regards, Francesca

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