Discussion Forum

Hello,

your boundary condition is unusual because it does not depend on the variable solved for, unless or depend on .

May I ask what physical conditions you are trying to model?

Hi Alexis

Thank you for your reply! Your guess is correct, is defined as an expression that depends on .

I'm dealling with a phase field model. I'm trying to model the flux of the phase field variable . However, the expression for the flux is non-standard, I couldn't use the flux/source node directly. I want to define my flux expression by myself. I know there is a boundary node called 'weak constraint' that allows me to define my own boundary condition. But when I applied this condition to my boundary, I kept getting an error telling me 'There are 293 void equations (empty rows in matrix) for the variable comp1.lm', where 'comp1.lm' is the Lagrange multiplier variable. I'm not familiar with weak consrtaint, so I don't know what this means.

Do you have any ideas on this problem? Or do you have any better ideas on how to implement this boundary condition?

Any advice will be much appreciated!

Hello Runzi,

Have you tried including into the definition of ?

Hi Alexis

Do you mean I do ,

where (some other parameters)?

Well, that's a good idea! I'll have a try.

Thank you!