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Simultaneous Boundary Conditions

Posted Sep 13, 2017, 8:04 a.m. EDT Modeling Tools & Definitions, Parameters, Variables, & Functions 3 Replies

Franky Prieto
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Hello,
I am making an exercise to reproduce a model with a set of PDE using math model in COMSOL, the model include a set of boundary conditions like this:
y=0 ---> Ψ = 0
y=0 ---> ∂Ψ/∂y = - S ∂θ/∂x
y=0 ---> ∂θ/∂y= 0
When I introduce the second one for the same differential equation overwrite the first one,
How can I introduce this simultaneous conditions?,
or simply COMSOL can not manage this?



3 Replies Last Post Sep 15, 2017, 8:36 p.m. EDT
Pu
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Posted: 7 years ago Sep 13, 2017, 11:52 a.m. EDT

I believe it is possible to do so. But maybe one should use some alternative form like constraint?

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ZHANG, Pu
School of Physics,
Huazhong University of Science and Technology
I believe it is possible to do so. But maybe one should use some alternative form like constraint?
Franky Prieto
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Posted: 7 years ago Sep 13, 2017, 1:25 p.m. EDT

I believe it is possible to do so. But maybe one should use some alternative form like constraint?

Thanks

I indroduce the second one as constraint, 0 = psiy + S * thetax in some time mixing 0 = thetay + psiy + S* thetax but solving with the last one can produce values for tethay=/=0

>I believe it is possible to do so. But maybe one should use some alternative form like constraint? Thanks I indroduce the second one as constraint, 0 = psiy + S * thetax in some time mixing 0 = thetay + psiy + S* thetax but solving with the last one can produce values for tethay=/=0
NDN UNIST/Mechanical Engineering
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Posted: 7 years ago Sep 15, 2017, 8:36 p.m. EDT

I guess that your governing equation including two function y & theta. So For the first one, you can apply directly by using Dirichlet BCs. But in case of second & third one, it should be better if you apply them as weak form by using Weak form Contribution. Because your BCs is the derivative form ( except for Neumman BCs ) Theorically, all the governing, BCs equation in COMSOL will be convert to Weak form. So onece you convert them to weak form, it means that you have already physically described your system BR.

I guess that your governing equation including two function y & theta. So For the first one, you can apply directly by using Dirichlet BCs. But in case of second & third one, it should be better if you apply them as weak form by using Weak form Contribution. Because your BCs is the derivative form ( except for Neumman BCs ) Theorically, all the governing, BCs equation in COMSOL will be convert to Weak form. So onece you convert them to weak form, it means that you have already physically described your system BR.

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