Boundary conditions [Solved]

[teepeeaye]

Dear Elmer users,

This question is about geometries for boundary conditions and geometry order.

If I have a model in 3D space (volume) is it possible to apply a boundary condition on a 1D geometry (line/edge) entity or even a 0D (point/node) entity?

• in general?
• using the GUI on a UNV format mesh produced by Salomé?

Thank you

[mika]

in general?

This may depend on the type of a boundary condition. Prescribing the value of the primary variable of a solver (a Dirichlet-type constraint) should generally work for 1-dimensional boundaries (provided the Elmer mesh file mesh.boundary contains information about the 1-dimensional boundaries) and also pointwise. For a Neumann-type condition (a natural BC) the support may depend somewhat on a physical model, so this may have exceptions.

[kevinarden]

I don't think you can do point in GUI, you have to use Target Node and target node is not in GUI, unless you use the free text window
If you read the unv into GUI then autoclean is automatic and will remove the edge elements
You can uses ElmerGrid without the autoclean flag to translate the mesh, the load the mesh into GUI to have the edge elements retained

[teepeeaye]

Thank you, I am considering a 3D Static Current Conduction with prescribed Voltage along a line as one of the boundaries.

[teepeeaye]

Thank you also (kevinarden) for the hint on execution and mesh handling.
It seems that the GUI for N dimensional space mainly considers N-1 dimensional boundaries.

[raback]

Hi

ElmerGUI only likes dim-1 dimension for BCs. ElmerSolver has no such limitations but that may not be helpful if the BCs are lost in translation.

However, you can create a dim-2 bc as intersection between two dim-1 boundaries. See test cases for usage:

Code: Select all

elmeruser@elmeruser-VirtualBox:~/elmerfem/fem/tests$ grep -ir 'intersection bc'
mgdyn_harmonic_wire_impedanceBC2/IBC_currdens.sif:  Intersection BC(2) = 1 4
IntersectionBCs/case.sif:  Intersection BC(2) = Integer 1 2
IntersectionBCs0D/case.sif:  Intersection BC(2) = Integer 1 5

-Peter

[teepeeaye]

So the answer is "Yes". Avoid the "-autoclean" in mesh conversion from UNV.
One way is to convert manually with:

Code: Select all

ElmerGrid 8 2 Mesh_1.unv

ElmerGrid help explains what happens with "-autoclean":

Code: Select all

-removelowdim        : remove boundaries that are two ranks lower than highest dim
-removeunused        : remove nodes that are not used in any element
-bulkorder           : renumber materials types from 1 so that every number is used
-boundorder          : renumber boundary types from 1 so that every number is used
-autoclean           : this performs the united action of the four above

and the one to avoid is "-removelowdim".

In the GUI I will expect this to be the case if you hit ^C and remove the "-autoclean" froom preferred elmergrid options. I didn't test this, as I did my job with ElmerGrid manually.

Thanks