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One boundary & Multiple boundary conditions

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Hello everyone I would like to ask why COMSOL can set temperature and heat flux boundary conditions at the same time, or why it can set mass fraction and flux boundary conditions at the same time. This is equivalent to setting two conditions on a boundary at the same time. Isn't that an overdetermined equation? I hope to get your help.


6 Replies Last Post 2022年3月16日 GMT+8 09:26
Acculution ApS Certified Consultant

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Posted: 2 years ago 2022年3月14日 GMT+8 15:49

Have you checked under the first condition that it is being overwritten by the second one?

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René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
Have you checked under the first condition that it is being overwritten by the second one?

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Posted: 2 years ago 2022年3月14日 GMT+8 21:39

Thank you for your answer. I checked and found that they coexisted. The first one was not overwritten by the second.

Thank you for your answer. I checked and found that they coexisted. The first one was not overwritten by the second.

Jeff Hiller COMSOL Employee

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Posted: 2 years ago 2022年3月14日 GMT+8 23:15
Updated: 2 years ago 2022年3月14日 GMT+8 23:16

Hello 佳卉,

In the Heat Transfer in Solids interface, which is what I assume you are using, the default BC is Thermal Insultation on all boundaries. If you add a Temperature BC on one of the boundaries, you will see that that boundary's number will be marked as "(overridden)" on the Thermal Insulation settings window.

Please post your mph file if this does not resolve your doubts.

Best,

Jeff

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Jeff Hiller
Hello 佳卉, In the Heat Transfer in Solids interface, which is what I assume you are using, the default BC is Thermal Insultation on all boundaries. If you add a Temperature BC on one of the boundaries, you will see that that boundary's number will be marked as "(overridden)" on the Thermal Insulation settings window. Please post your mph file if this does not resolve your doubts. Best, Jeff

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Posted: 2 years ago 2022年3月15日 GMT+8 19:16

Thank you for your answer. I understand what you mean. What I don't understand is that when I add "temperature" BC (Dirichlet condition) on a boundary, I can also add "flux" BC (Neumann condition) on this boundary. Their relationship is coexistence. I don't understand why these two boundary conditions can coexist.

Thank you for your answer. I understand what you mean. What I don't understand is that when I add "temperature" BC (Dirichlet condition) on a boundary, I can also add "flux" BC (Neumann condition) on this boundary. Their relationship is coexistence. I don't understand why these two boundary conditions can coexist.

Jeff Hiller COMSOL Employee

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Posted: 2 years ago 2022年3月15日 GMT+8 20:47
Updated: 2 years ago 2022年3月15日 GMT+8 20:48

Hello 佳卉,

I think I now understand your question. The section of the Reference Guide entitled "Physics Exclusive and Contributing Node Types" (on pages 172-173 in the documentation for v 6.0) addresses your question, especially the paragraph at the bottom of page 172 ("Order of exclusive and contributing nodes").

The Reference Guide can be accessed through File > Help > Documentation. Best,

Jeff

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Jeff Hiller
Hello 佳卉, I think I now understand your question. The section of the Reference Guide entitled "Physics Exclusive and Contributing Node Types" (on pages 172-173 in the documentation for v 6.0) addresses your question, especially the paragraph at the bottom of page 172 ("Order of exclusive and contributing nodes"). The Reference Guide can be accessed through File > Help > Documentation. Best, Jeff

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Posted: 2 years ago 2022年3月16日 GMT+8 09:26

Thank you very much for your help. Now I understand this question by reading the help document.

Thank you very much for your help. Now I understand this question by reading the help document.

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