Discussion Forum

Hi,
I am a rather new user and do not have a lot of experience with COMSOL or numerics.

I have a pseudo 1D non-linear PDE which is defined on 3 different domains. The reason the model is psuedo 1D is that I have taken into account 3D geometry concerns and transformed them into a 1D model (symmetry reasons). Hence, for each domain the conservative flux and forces are defined differently.

So my model uses the General Form PDE physics module. Each domain has three variables. The equations have been defined separately for each domain. I have imposed Dirchelet BC on the edges of domain 1 and 3. Now I am struck with two problems:
1. I would like to impose the following BC between domain 1 and 2 (and domain 2 and 3). So for one of the variables lets say c1, how do i define the flux between (c1,1)=(c1,2)/2. where the number after the comma defines the domain number? Should I be using a constrain BC or Source BC? If so,how? I do not completely understand the explainations given in chapter 15 of the COMSOL manual.
2. When I imposed continuity (just to see if my models works) I have discovered that when I do not enter a good enough initial value, the program is unable to solve the problem. Why do I need initial values for a stationary solution? Why does this effect the solution in such a way? How do I raise the number of allowed iterations?

Thank You,
Yoav