# 2D simply supported beam boundary conditions **URL:** \ **Category:** mesh\ **Created:** [August 10, 2022, 2:09pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975 "2022-08-10T14:09:03Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![dries](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dries/32/4059_2.png) [@dries](https://fenicsproject.discourse.group/u/dries)\ **Post date:** [August 10, 2022, 2:09pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/1 "2022-08-10T14:09:03Z")
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. ```auto # Boundary conditions leftsup = CompiledSubDomain("(near(x[0], 0.0) && near(x[1], 0.0))") rightsup = CompiledSubDomain("(near(x[0], 40.0) && near(x[1], 0.0))") leftload = CompiledSubDomain("(near(x[0], 10.0) && near(x[1], 4.0))") rightload = CompiledSubDomain("(near(x[0], 30.0) && near(x[1], 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") bcleftload = DirichletBC(W.sub(1), load, leftload, "pointwise") bcrightload = DirichletBC(W.sub(1), load, rightload, "pointwise") bc_u = [bcleftsup, bcrightsup, bcleftload, bcrightload] boundaries = MeshFunction("size_t", mesh, mesh.topology().dim() - 1) boundaries.set_all(0) leftload.mark(boundaries,1) rightload.mark(boundaries,2) ds = Measure("ds")(subdomain_data=boundaries) n = FacetNormal(mesh) ``` ---
**Author:** ![nate](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/nate/32/17_2.png) [@nate](https://fenicsproject.discourse.group/u/nate)\ **Post date:** [August 10, 2022, 2:10pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/2 "2022-08-10T14:10:54Z")
Please see [Read before posting: How do I get my question answered?](https://fenicsproject.discourse.group/t/read-before-posting-how-do-i-get-my-question-answered/21) regarding how to construct a MWE. ---
**Author:** ![dries](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dries/32/4059_2.png) [@dries](https://fenicsproject.discourse.group/u/dries)\ **Post date:** [August 11, 2022, 1:16pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/3 "2022-08-11T13:16:44Z")
I edited my post. Could you please answer my question now? ---
**Author:** ![nate](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/nate/32/17_2.png) [@nate](https://fenicsproject.discourse.group/u/nate)\ **Post date:** [August 11, 2022, 1:18pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/4 "2022-08-11T13:18:26Z")
Your code is incomplete. Your error message states: ```auto “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. ---
**Author:** ![dries](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dries/32/4059_2.png) [@dries](https://fenicsproject.discourse.group/u/dries)\ **Post date:** [August 11, 2022, 1:23pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/5 "2022-08-11T13:23:52Z")
Thank you. This is how I defined my mesh. ```auto # 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) ``` ---
**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\ **Post date:** [August 11, 2022, 2:45pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/6 "2022-08-11T14:45:52Z")
As you are using an xml file one cannot reproduce your issue. I would suggest you write > [@dries](#): > > ```auto > boundaries = MeshFunction("size_t", mesh, mesh.topology().dim() - 1) > boundaries.set_all(0) > leftload.mark(boundaries,1) > rightload.mark(boundaries,2) > > ``` `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. ---
**Author:** ![dries](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dries/32/4059_2.png) [@dries](https://fenicsproject.discourse.group/u/dries)\ **Post date:** [August 11, 2022, 3:15pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/7 "2022-08-11T15:15:16Z")
When I do that, I just see the mesh. The boundaries are not present. ---
**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\ **Post date:** [August 11, 2022, 3:23pm UTC](https://fenicsproject.discourse.group/t/2d-simply-supported-beam-boundary-conditions/8975/8 "2022-08-11T15:23:52Z")
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.