Hi, I was wandering what happens if, in a time dependent problem (Navier-Stokes type for example) I only specify Dirichlet boundary conditions in a subset of the whole boundary. How does FEniCS solve the equations? What values are given to the unused points in the boundary?

Thanks!

You question is too broad to be answered briefly in this forum. I suspect the answer is along the lines of â€śremaining boundary terms will correspond to natural enforcement of zero stressâ€ť; however, thereâ€™s not enough detail in your question regarding your formulation and implementation to be sure.

I suggest looking at @dokkenâ€™s excellent tutorial, specifically:

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