# 2D simply supported beam boundary conditions

Hi. I am trying to model 2D simply supported beam in Fenics but I am getting “Warning: Found no facets matching domain for boundary condition”. Thank you.
The code is below.

``````# Boundary conditions
leftsup = CompiledSubDomain("(near(x, 0.0) && near(x, 0.0))")
rightsup = CompiledSubDomain("(near(x, 40.0) && near(x, 0.0))")
leftload = CompiledSubDomain("(near(x, 10.0) && near(x, 4.0))")
rightload = CompiledSubDomain("(near(x, 30.0) && near(x, 4.0))")

load = Expression("t", t = 0.0, degree=1)

bcleftsup= DirichletBC(W, Constant((0.0,0.0)), leftsup, "pointwise")
bcrightsup= DirichletBC(W, Constant((0.0,0.0)), rightsup, "pointwise")

boundaries = MeshFunction("size_t", mesh, mesh.topology().dim() - 1)
boundaries.set_all(0)

ds = Measure("ds")(subdomain_data=boundaries)
n = FacetNormal(mesh)
``````

Please see Read before posting: How do I get my question answered? regarding how to construct a MWE.

I edited my post. Could you please answer my question now?

Your code is incomplete. Your error message states:

`````` “Warning: Found no facets matching domain for boundary condition”
``````

which is an issue with your geometry. But we cannot help without seeing how your mesh is defined.

Thank you. This is how I defined my mesh.

``````# mesh
from dolfin import *
mesh = Mesh('beam.xml')

# Define Space
V = FunctionSpace(mesh, 'CG', 1)
W = VectorFunctionSpace(mesh, 'CG', 1)
WW = FunctionSpace(mesh, 'DG', 0)
p, q = TrialFunction(V), TestFunction(V)
u, v = TrialFunction(W), TestFunction(W)
``````

As you are using an xml file one cannot reproduce your issue.

I would suggest you write

`boundaries` to file and visualize in paraview to make sure it works as expected.
Similarly you should mark the other boundaries as well to make sure they do what they expect.

1 Like

When I do that, I just see the mesh. The boundaries are not present.

That means that your markers are not working as you think they should.
This means that you need to either:

1. Revisit the creation of the mesh, and for instance import markers from the `xml`/`xmdf` file of the mesh directly.
2. Rethink your markers, as they are not marking anything, are you sure they are expressing the correct condition.