# Custom constraint on variables on domains interface

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October 8, 2013, 02:41
Custom constraint on variables on domains interface
#1
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Join Date: Feb 2011
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Hello everyone!

I wonder if there any way to set custom constraint on a variables on interface between domains? Specifically how can I set value of variable v1 on one side of interface as function of variable v2 on other side of interface while v2 is determined during solution (and as a consequence v1)? v1 and v2 are both local but not integral variables.

Is it possible to do this without utilizing user fortran?
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 October 8, 2013, 03:07 #2 New Member   Join Date: Nov 2010 Posts: 5 Rep Power: 9 Dear Antanas, I'm not a expert on CFD. But from a momentum flux conservation viewpoint, the average velocity (for incompressible flow) on each side of the interface should be equal. I wonder what kind of relationship between v1 and v2? The function f() must satisfy the momentum conservation pricinple, so there must be some parameter in f() depends on the integration of v2. It seems there is not any simple method without UDF to solve your problem. Just some personal thought. Expecting better answers. pz21

October 8, 2013, 04:31
#3
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Quote:
 Originally Posted by pz21 Dear Antanas, I'm not a expert on CFD. But from a momentum flux conservation viewpoint, the average velocity (for incompressible flow) on each side of the interface should be equal. I wonder what kind of relationship between v1 and v2? The function f() must satisfy the momentum conservation pricinple, so there must be some parameter in f() depends on the integration of v2. It seems there is not any simple method without UDF to solve your problem. Just some personal thought. Expecting better answers. pz21
Actually v1, v2 are not necessarily velocities. They may be for example electric potential. I want that its value on one side of interface be a function of its value on other side. For example v2 = (v1 - A), where A may (not) be constant.

 October 8, 2013, 05:25 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,336 Rep Power: 110 This is straight forward to do using a source term. If you are talking about algebraic quantities then you can just make a function of whatever you like. But implementation is one thing, obtaining convergence is another - weird source terms are difficult (even impossible) to converge.

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