I am trying to learn Gmsh and Fenics and was looking at an example which shows the application of Boundary conditions on a simple Poisson problem.
Here is the link:
The example defines the domain Ω to be a model of blood vessels with an aneurysm. It has one inlet vessel and two outlet vessels. They define no slip boundary conditions on the walls of the vessels and aneurysm, that is u=u0=0.0. We let u=u1=1.0 be the Dirichlet condition on the inlet, the outlets will have the prescribed values u=u2=2.0 and u=u3=3.0. In summary, we have:
u=u0=0.0 on ΓD,0 (noslip boundary); u=u1=1.0 on ΓD,1 (inlet); u=u2=2.0 on ΓD,2 (outlet 1) ; u=u3=3.0 on ΓD,3 (outlet 2) ; f=0.0 (source term)
I can understand the code overall, but I am unable to understand the meaning of these Boundary conditions, i.e., unable to visualize them in a physical sense, intuitively. I' ll appreciate if you can post any other link or better example too which explains the BC phenomena better.