Do you mean a Cauchy condition?
One very easy way is to use a Pointwise constraint and set your condition there (you might need to activate the advanced options).
This will make the expression you write equal to zero in the specified domain (boundary, edge or point). So if you want to say a=b, then write a-b, etc. Read that fabulous manual for details.
Alternatively you can also check weak constraints and Dirichlet BCs Yes, you can use Dirichlet to impose a Newman condition too! If you want to set ux=g, then write u+ux-g in the Dirichlet box for variable u. This makes u=u+ux-g, or ux=g. There are many ways of doing this. Read that fabulous manual for details.
And also look at the discussion forum:
http://www.comsol.com/community/forums/general/thread/32683/
Best Regards,
V
Post by janice.white24Hi! Everyone. I am using Comsol 4.2a and I found a difficult question for me when using general PDE. I want to set one boundary satisfying Newmann Boundary and Dirichlet Boundary condition at the same time, but I failed to add both of them. I wonder whether anyone can give me a help? I will be very appreciated since I have been stuck in this question for several days...........................
Thank you!!