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Dirichlet and Neumann BC for a boundary
Posted Feb 8, 2011, 7:09 a.m. EST 2 Replies
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Dear all,
I have a question maybe simple one. How can I define 2 boundary conditions for one boundary? one Dirichlet Bc and one Neumann bc for the entrance? I'm working with PDE module and I want to set both flux (by Neumann bc ) and state (by Neumann BC ) at the interance because I know both. by state I mean I know the value of my dependent variable at the entrance.
In comsol 3.5a I see that I either can select Dirichlet OR Neumann NOT BOTH.
Many thanks in advance,
Elham
I have a question maybe simple one. How can I define 2 boundary conditions for one boundary? one Dirichlet Bc and one Neumann bc for the entrance? I'm working with PDE module and I want to set both flux (by Neumann bc ) and state (by Neumann BC ) at the interance because I know both. by state I mean I know the value of my dependent variable at the entrance.
In comsol 3.5a I see that I either can select Dirichlet OR Neumann NOT BOTH.
Many thanks in advance,
Elham
2 Replies Last Post Feb 8, 2011, 8:08 a.m. EST
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Posted:
1 decade ago
Hi
you can't. This would be an overdeterminacy.
Setting up a dirichlet BC implies a neumann BC with the lagrange multiplier. So the flux (neuman BC) is calculated to balance the prescribed direct value of your dependant variable.
In other words: if you use a Dirichlet BC you are already setting up a Neumann BC as well - but you can't see it directly. In postprocessing mode you have access to these lagrange multipliers using the reacf() Operator.
kind regards
you can't. This would be an overdeterminacy.
Setting up a dirichlet BC implies a neumann BC with the lagrange multiplier. So the flux (neuman BC) is calculated to balance the prescribed direct value of your dependant variable.
In other words: if you use a Dirichlet BC you are already setting up a Neumann BC as well - but you can't see it directly. In postprocessing mode you have access to these lagrange multipliers using the reacf() Operator.
kind regards
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Posted:
1 decade ago
Thanks Kia for your help. I agree with you.
Regards,
Elham
Regards,
Elham