I would like to solve a Laplace equation on a 2D domain built as a polygon. I would like to set up a combination of Dirichlet boundary conditions on different portions of the boundary. How do I select a desired portion of a boundary (i.e, a portion of a polygon)? To be more specific here is an ex…

Thanks for a reply. I can try external software if necessary, but is there still a way of marking parts of a boundary inside fenics? I already have a mesh build in fenics.

Yes, if you have some Notion of Which parts of the boundary should be marked, you could follow the strategy outlined in this tutorial . In for the mesh above, i guess that would be x[0]>1e-14 and x[0]<1-eps and x[1]>1 and on_boundary

Thanks again, I have read that tutorial. In that tutorial the irregular boundary corresponds to a single domain. My problem is different. My earlier example above was not a very good example. My actual problem has a more irregular geometry where facets do not align with the x and y axis. For example…

Hello @dokken . What if I have a mesh saved in a file with some markers set on some cells? Say 1 and 0 on different cells. I can load the mesh from file in my fenics python script, but I don’t understand how can I use marker values to set boundary conditions. All functions that set bc that i’ve found…

Then you need to load a MeshFunction. As shown in Transitioning from mesh.xml to mesh.xdmf, from dolfin-convert to meshio you load the mesh function mf And use that In the DirichletBC, As shown in the Stokes demo

Thank you for your reply. Quoting from your example: mesh = Mesh() with XDMFFile("mesh.xdmf") as infile: infile.read(mesh) I have a file mesh.xdmf where I have several fields, and among one of them I have a cell field named ‘composition’ with some cells have value 0 and others have value 1. Ca…

You can use functions that describe your boundary curves (lines) and use the fact that the boundary DOF locations must lie on (or near) the curve within the endpoint constraints for each curve segment. For example: class BorderBC(SubDomain): def inside(self, x, on_boundary): r = (y1 - …

Please provide a minimal example with an error message if the suggested code does not work. But you Need to save boundary data as a separate file for dolfin to read it in. If you are reading in cell data, you can store it alongside the mesh

That’s the snipped I’m trying to use: mesh = Mesh() with XDMFFile("/tmp/mesh.xdmf") as infile: infile.read(mesh) mvc = MeshValueCollection("size_t", mesh, 2) with XDMFFile("/tmp/mf.xdmf") as infile: infile.read(mvc, "bc") mf = cpp.mesh.MeshFunctionSizet(mesh, mvc) V = FunctionSpace(mesh,…

How to define boundary conditions on an irregular geometry?

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dokken January 18, 2020, 8:25am 2

For more complicated geometries , its common to use external software, like gmsh/pygmsh. With these softwares, you can set physical markers for cells snd facets, Which can be loaded into dolfin as described here:

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How to define boundary conditions on an irregular geometry?

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