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Comsol help write a boundary condition

  1. Dec 23, 2008 #1
    Hi there,

    I'm using comsol for the first time, and I think I've got everything working, except that I need to write a boundary condition that is dependent upon the gradient of a variable. How do I tell Comsol to take the gradient? I suppose I can define my own function, but I don't even know where to begin... (Man, comsol's support is not up to par. I don't think they even have a list of functions available anywhere.)

    Thanks so much,
  2. jcsd
  3. Dec 28, 2008 #2


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    Science Advisor
    Gold Member

    Hi, you could use the "diff" internal function or then its shorthand, like ux is diff(u,x) and then it in the BC. Yeah, getting going with this software isn't quite as fast as with several others.
  4. Jan 23, 2009 #3
    All the syntax for COMSOL is taken from Matlab, so if you are familiar with the latter the former is pretty comfy. You can also send e-mails to help@comsol.com (or something like this) and they will tell you how to do stuff. There is also a forum on their website you can search, i often find helpful stuff there. Finally, the model library is very useful! Just find a model that is similar to yours and look inside to see how they did it. You can even save the whole model as an m-file and read out the syntax of all the commands.

    Actually, i think there is even a gradient boundary condition type depending on what your application mode is... Just define the variable in the appropriate variable table and then insert it in the space provided in the boundary condition tab.
  5. Sep 13, 2010 #4
    diff (u,x) is not supported in v4. Any idea how to use it there?
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