The problem in a simple example I made and how to 'project' the value assigned to 'FunctionSpace' into a numpy array in dolfinx environment?

dolfinx
11

You are getting different results because your old DOLFIN code and DOLFINx code are using different meshes ("right/left" for old DOLFIN and dolfinx.mesh.DiagonalType.right for DOLFINx). See screenshot below

screenshot2
screenshot21484×755 72.1 KB

If you change your DOLFINx mesh generation code to the following, you should see that the solutions are identical

msh = mesh.create_rectangle(
    MPI.COMM_WORLD,
    ((0.0, 0.0), (nelx, nely)),
    (nelx, nely),
    cell_type=mesh.CellType.triangle,
    diagonal=mesh.DiagonalType.right_left,
)

As a final note, your code in old DOLFIN is also applying the traction to the entire right boundary, not a point load at the bottom right corner. The following statement marks all facets on the right boundary because x[1]<=2 is true for all points on the right boundary.

If you want to apply a point load at the bottom right corner, you should use PointSource in old DOLFIN (see here and here). Unfortunately, the reimplementation in DOLFINx is not complete yet; see PointSource in dolfinx.

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