Menu

Discussion Forum

New Discussion
Filter

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 The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

How to specify different boundaries in an equation

Posted Mar 30, 2012, 4:06 p.m. EDT Version 4.3b 5 Replies

Ray
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

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 Nov 16, 2013, 6:22 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Mar 31, 2012, 2:17 p.m. EDT
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Apr 1, 2012, 11:15 p.m. EDT
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Apr 2, 2012, 10:31 p.m. EDT
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Nov 15, 2013, 1:58 p.m. EST
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Nov 16, 2013, 6:22 p.m. EST
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.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content