Axisymmetric: Number of Dofs smaller than dim: 2 vs. 3 [Solved]

[teepeeaye]

Hello Elmer users,

I try to make a 2D axi symmetric thermo mechanical analysis using the GUI.
The simulation section of the generated .sif file is:

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Simulation
  Max Output Level = 5
  Coordinate System = Axi Symmetric
  Coordinate Mapping(3) = 1 2 3
  Simulation Type = Steady state
  Steady State Max Iterations = 1
  Output Intervals(1) = 1
  Solver Input File = case.sif
  Post File = case.vtu
End

I read the mesh from a UNV file and the mesh works fine when I do the analysis with code_aster and the mesh is arranged in the XY plane so the axis of symmetry _is_ the Y axis. First step is a thermal analysis. The thermal - when run alone - completes and generates a vtu output.

However - no matter what I have tried I get this error when adding the next step to calculate displacements and stresses:

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ERROR:: StressSolver: Number of Dofs smaller than dim: 2 vs. 3

As I have succesfully done similar analysis in the past I suspect that the analysis setup in Elmer should be OK and after shooting in several directions in the blind I ended up looking at the UNV mesh file. The first lines are like below:

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    -1
   164
         1  SI: Meter (newton)         2
    1.0000000000000000E+0    1.0000000000000000E+0    1.0000000000000000E+0
    2.7314999999999998E+2
    -1
    -1
  2420
         1
SMESH_Mesh
         1         0         0
Global Cartesian Coordinate System
    1.0000000000000000E+0    0.0000000000000000E+0    0.0000000000000000E+0
    0.0000000000000000E+0    1.0000000000000000E+0    0.0000000000000000E+0
    0.0000000000000000E+0    0.0000000000000000E+0    1.0000000000000000E+0
    0.0000000000000000E+0    0.0000000000000000E+0    0.0000000000000000E+0
    -1
    -1
  2411
         1         1         1        11
   6.2500000000000000E-02  -5.3380000000000005E-01  -3.1064040229011879E-17
         2         1         1        11
   1.8499999999999999E-02  -5.3380000000000005E-01  -3.1064040229011879E-17
         3         1         1        11
   1.8499999999999999E-02  -5.1378999999999997E-01  -2.8842483956736944E-17
         4         1         1        11
   3.5000000000000003E-02  -5.1378999999999997E-01  -2.8842483956736944E-17
         5         1         1        11
   3.5000000000000003E-02  -5.0900000000000001E-01  -2.8310687127941492E-17

My suspicion was "imperfection" of the Z-coordinate not being exacly zero, leaving med with a few questions to the wiser and/or more experienced:

Could that be the issue?
If so, is there a setting in ElmerGUI/ElmerGrid that I can use to eliminate that behaviour (e.g. force the mesh to be 2D)?
If not so - what can I be doing wrong?

I use Elmer v. 9

[teepeeaye]

Seems I answered my question.

To resolve I did the following shell commands in the project directory:

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mv mesh.nodes mesh.nodes.z
awk "{printf (\"%g %g %g %g %g\n\",\$1,\$2,\$3,\$4,0)}" < mesh.nodes.z > mesh.nodes

The result was a mesh.nodes where the z-coordinate was forced exactly zero. That did the trick.
Maybe this can be of value to other users