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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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discontinuous BC

Posted 2012年6月7日 GMT-4 02:00 Version 4.2a 8 Replies

EH Ooi
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Hi,
I am attempting to use Identity Pair or perhaps Contact Pair to prescribe a flux boundary condition at an interior boundary. However, when I solved the model and plot the flux across the interior boundary, it is different from the function of the boundary condition. I am solving the Helmholtz equation.

I have attached the file here and Identity Pair 1 is where the discontinuous boundary condition is prescribed. Can someone see if anything is wrong?

Thank you.



Best regards,
EH

Attachments:

8 Replies Last Post 2012年6月7日 GMT-4 05:57
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2012年6月7日 GMT-4 02:11
Hi

why bother using "assembly mode" if its to apply default continuity, its much easier to remain in "Union" mode and rely on COMSOLs internal settings of continuity on common boundaries

--
Good luck
Ivar
Hi why bother using "assembly mode" if its to apply default continuity, its much easier to remain in "Union" mode and rely on COMSOLs internal settings of continuity on common boundaries -- Good luck Ivar
EH Ooi
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Posted: 1 decade ago 2012年6月7日 GMT-4 02:15
Hi Ivar,
That model was set at continuity because I am not sure which Pair condition I should use to prescribe a discontinuous flux. In fact, I have used Flux/Source (under pair node) and the results are still the same. i.e. when I plot the flux on the interior boundary, the distribution is different from the function that is being prescribed. I would like to have the flux at the interior boundary to be the same but a discontinuous potential.

Thank you.

Best wishes,
EH
Hi Ivar, That model was set at continuity because I am not sure which Pair condition I should use to prescribe a discontinuous flux. In fact, I have used Flux/Source (under pair node) and the results are still the same. i.e. when I plot the flux on the interior boundary, the distribution is different from the function that is being prescribed. I would like to have the flux at the interior boundary to be the same but a discontinuous potential. Thank you. Best wishes, EH
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2012年6月7日 GMT-4 02:18
Hi

then have you tried Thin resistive layer BCs ?

--
Good luck
Ivar
Hi then have you tried Thin resistive layer BCs ? -- Good luck Ivar
EH Ooi
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Posted: 1 decade ago 2012年6月7日 GMT-4 02:21
I am using the PDE mode and solving the Helmholtz equation. I dont think there is an option to select the thin resistive layer BC in this physics or am I wrong?

Thank you.


EH
I am using the PDE mode and solving the Helmholtz equation. I dont think there is an option to select the thin resistive layer BC in this physics or am I wrong? Thank you. EH
EH Ooi
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Posted: 1 decade ago 2012年6月7日 GMT-4 03:09
Hi again,
Did you mean contact pair when you said thin resistive layer? I have tried that but I am still getting a different flux distribution across the interior boundary than the function that I prescribed. However, I cannot be certain if I am doing it correctly.


Thank you.


Best regards,
EH
Hi again, Did you mean contact pair when you said thin resistive layer? I have tried that but I am still getting a different flux distribution across the interior boundary than the function that I prescribed. However, I cannot be certain if I am doing it correctly. Thank you. Best regards, EH
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2012年6月7日 GMT-4 04:50
Hi

you are right in "pure math mode" you need to define your surface layers with assembly and pair identity or linked flux (contact is normally for structural)

--
Good luck
Ivar
Hi you are right in "pure math mode" you need to define your surface layers with assembly and pair identity or linked flux (contact is normally for structural) -- Good luck Ivar
EH Ooi
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Posted: 1 decade ago 2012年6月7日 GMT-4 05:25
Hi,
I have just found out that if I check the box for 'Create Imprint' then I am able to specify the flux at the interior boundary. The results are more acceptable but there is still one nagging problem. Across the interior boundary where the flux BC is prescribed, the magnitude appears to be different, which would suggest discontinuity in the flux. However the potential across the top and bottom surfaces are identical, i.e. the potential is continuous across the interior boundary. I am curious as to why the potential is continuous and flux discontinous and not the other way round?


Best wishes,
EH
Hi, I have just found out that if I check the box for 'Create Imprint' then I am able to specify the flux at the interior boundary. The results are more acceptable but there is still one nagging problem. Across the interior boundary where the flux BC is prescribed, the magnitude appears to be different, which would suggest discontinuity in the flux. However the potential across the top and bottom surfaces are identical, i.e. the potential is continuous across the interior boundary. I am curious as to why the potential is continuous and flux discontinous and not the other way round? Best wishes, EH
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2012年6月7日 GMT-4 05:57
Hi

depending on your physics you might have a mesh density issue around the discontinuity, as if you work on fluxes these are often derivatives of the depedent variables hence might become "ragged" for coarse meshing.

check your mesh sensitivity, and perhaps increase the discretization order of the mesh elements

--
Good luck
Ivar
Hi depending on your physics you might have a mesh density issue around the discontinuity, as if you work on fluxes these are often derivatives of the depedent variables hence might become "ragged" for coarse meshing. check your mesh sensitivity, and perhaps increase the discretization order of the mesh elements -- Good luck Ivar

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