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Are constraints always global?

Posted 2 mars 2012, 12:32 UTC−5 Studies & Solvers Version 3.5a 3 Replies

Pu
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Here's a strange problem...

For a supposed one-way coupling model, variable Hz from Module1 is used as the input for Module2. There should be no backward coupling. In Module2 I have a constraint for dependent variable of Module2 on boundary including Hz. When solving the model in two steps, even I only solve Module1 by sequence, the results are influenced by the constraint in Module2, that is, the constraint is seen as global and solved as well.

To get rid of the influence of the constraint on Hz, I turned off the constraint when solving the first step. In the second step I turn it on and solve only Module2. Surprisingly, the results of Hz from the first step solution is even changed by the second step...

Now that the constraint is global, is there any way I can realize a constraint locally in Module2?

Thanks a lot!
3 Replies Last Post 3 mars 2012, 11:31 UTC−5
Pu
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Posted: 1 decade ago 3 mars 2012, 07:48 UTC−5
I guess what COMSOL does for coupled problems is first assembling all equations. For my case, I would like to solve only one dependent variable from one module. COMSOL looks around the equations for this variable, and solves equations including the variable with other dependent variables set to either zero or current solution. Since the variable appears in a constraint, the constraint is considered. The problem is the preassigned values of other dependent variables don't make the constraint a dummy one, thus having influence on the results.
I guess what COMSOL does for coupled problems is first assembling all equations. For my case, I would like to solve only one dependent variable from one module. COMSOL looks around the equations for this variable, and solves equations including the variable with other dependent variables set to either zero or current solution. Since the variable appears in a constraint, the constraint is considered. The problem is the preassigned values of other dependent variables don't make the constraint a dummy one, thus having influence on the results.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 3 mars 2012, 07:58 UTC−5
Hi

are you sure you have decoupled the solver, one for each and that he solvers are not in fact solving both physics without you noticing it ?

Havent used 3.5 for too long, cannot remember where you set whch solver acts on which physics, but there should be a matrix entry somewhere

--
Good luck
Ivar
Hi are you sure you have decoupled the solver, one for each and that he solvers are not in fact solving both physics without you noticing it ? Havent used 3.5 for too long, cannot remember where you set whch solver acts on which physics, but there should be a matrix entry somewhere -- Good luck Ivar
Pu
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Posted: 1 decade ago 3 mars 2012, 11:31 UTC−5
Thanks for ur reply!

I think I did the right thing to decouple modules. I set specific dependent variables in "Solve For" tab of "Solver Manager", and used "Values of variables not solved for and linearization point" to assign values for other dependent variables not solved for.

According to my thoughts, I can understand most things here, except one thing: The second step of solving even alters the value of the dependent variable I didn't specify as "Solved For".
Thanks for ur reply! I think I did the right thing to decouple modules. I set specific dependent variables in "Solve For" tab of "Solver Manager", and used "Values of variables not solved for and linearization point" to assign values for other dependent variables not solved for. According to my thoughts, I can understand most things here, except one thing: The second step of solving even alters the value of the dependent variable I didn't specify as "Solved For".

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