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How to specify different boundaries in an equation

Posted 30.03.2012, 16:06 GMT-4 Version 4.3b 5 Replies

Ray
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There are two boundaries in my model: Boundary A and Boundary B. Boundary A is located at x = 0 cm, while Boundary B is located x = 2 cm. There is an equation which is a boundary condition:

-q*(∇u2) = 1.5* (u(A)-u5(B)-E(B))/(q*R)

Where A and B refer to Boundary A and Boundary B. u, u2 and u5 are the electric potential of electrons, iodide ions and the electrostatic potential, respectively.

My question is: how do I specify these two boundaries in this equation of boundary condition? How do I tell the computer that I want to use the value of u at Boundary A and the values of u5 and E at boundary B? I try to type this as the "g" value of the Neumann boundary condition:

1.5* (u(x=0)-u5(x=2)-E(x=2))/(q*R)

but it doesn't work.

Thank you!



5 Replies Last Post 16.11.2013, 18:22 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 31.03.2012, 14:17 GMT-4
Hi

I havnt really read if you are in 1D or 2D, but if its 1D you should make a global variable out of your dependent values t the different boundaries, then you can refer to tem ynwhere, else you need the coupling projection operators to map the results at one location to another, check the doc.

do not forget that dependent vriables are in fact fields u(x,y,z) so you need to refer to thes eimplicit locations via the selections

--
Good luck
Ivar
Hi I havnt really read if you are in 1D or 2D, but if its 1D you should make a global variable out of your dependent values t the different boundaries, then you can refer to tem ynwhere, else you need the coupling projection operators to map the results at one location to another, check the doc. do not forget that dependent vriables are in fact fields u(x,y,z) so you need to refer to thes eimplicit locations via the selections -- Good luck Ivar
Ray
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Posted: 1 decade ago 01.04.2012, 23:15 GMT-4
Hi Ivar,

It is a 3-D model. But only the direction along X axis matters. Thanks
Hi Ivar, It is a 3-D model. But only the direction along X axis matters. Thanks
Ray
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Posted: 1 decade ago 02.04.2012, 22:31 GMT-4
Hi Ivar,

Thank you very much for your answer. Can you explain it a little more? I'm really new to Comsol...
Hi Ivar, Thank you very much for your answer. Can you explain it a little more? I'm really new to Comsol...
Marco Zanoni
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Posted: 1 decade ago 15.11.2013, 13:58 GMT-5
Hi Ray,

Did you fix your problem?

I have the same problem and I can't figure it out.

Thanks.

Marco
Hi Ray, Did you fix your problem? I have the same problem and I can't figure it out. Thanks. Marco
Jim Freels mechanical side of nuclear engineering, multiphysics analysis, COMSOL specialist
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Posted: 1 decade ago 16.11.2013, 18:22 GMT-5
In the physics portion of the model tree, right click on the boundary section, look for the boundary condition you want to specify, insert the boundary number corresponding to the location where you want it to be. It is intuitive.
In the physics portion of the model tree, right click on the boundary section, look for the boundary condition you want to specify, insert the boundary number corresponding to the location where you want it to be. It is intuitive.

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