• hotti
  • New member
  • Offline
  • From: Germany
  • Registered: 18-09-2012
  • Posts: 1

Topic: nodes and elements

Hey Guys,



I'm new to oofem and i have a question about the node and element definition.
I tried to understand the code in the file test41.in.



I would like to know what this is.
After >node< follows the number... and then...3 coordinates? with x,y,phi?
What is bc? boundary conditions? If 0 means no bc and 1 means a bc in y, why is in node 6 a 2?


node 1 coords 3 0.  0.  0.  bc 3 0 1 0
node 2 coords 3 2.4 0.  0.  bc 3 0 0 0
node 3 coords 3 3.8 0.  0.  bc 3 0 0 1
node 4 coords 3 5.8 0.  1.5 bc 3 0 0 0 load 1 4
node 5 coords 3 7.8 0.  3.0 bc 3 0 1 0
node 6 coords 3 2.4 0.  3.0 bc 3 1 1 2

What does DofsToCondense mean?


Beam2d 1 nodes 2 1 2 mat 1 crossSect 1 boundaryLoads 2 3 1 bodyLoads 1 5
Beam2d 2 nodes 2 2 3 mat 1 crossSect 1 DofsToCondense 1 6  bodyLoads 1 5
Beam2d 3 nodes 2 3 4 mat 1 crossSect 1 DofsToCondense 1 3
Beam2d 4 nodes 2 4 5 mat 1 crossSect 1
Beam2d 5 nodes 2 6 2 mat 1 crossSect 1 DofsToCondense 1 6

You see, i'm a bit confused.

Greetings from Germany,
H

  • From: Gothenburg, Sweden
  • Registered: 08-09-2009
  • Posts: 1,419

Re: nodes and elements

Hi hotti.

After keywords that contain vectors, you need to specify the length of that vector so
"coords 3 0. 0. 0."
means that "coords" is a vector with 3 components, x, y, and z (these are coordinates, not unknown degrees of freedom, so of course phi doesn't ever come into this).

"bc 3 0 1 0"
mean that bc has, again, 3 components.
The unknowns are for this type of problem added automatically, and will be in the order; displacement in x, displacement in z, rotation around y. (again, this has nothing to do with the coordinates)
0 means no boundary condition, any nonzero number means that boundary condition (the listen boundary conditions are also numbered).
So boundary condition 1 will be applied to the degree of freedome representing displacement in y

In node 6 boundary condition 1 is applied to displacement in x and z, and boundary condition 2 is applied to rotation around y.

The element manual explains what the special parameters mean
http://www.oofem.org/resources/doc/elem … ode10.html

  • hotti
  • New member
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  • From: Germany
  • Registered: 18-09-2012
  • Posts: 1

Re: nodes and elements

Thanks Mikael,

this was really helpfull.


Perhaps you can tell me what i have to do if i want to simulate a CAD file like *.stl.
I tried to mesh a geometry with "gmsh" but i didn't figured out how to get the boundary conditions in the generated mesh. Is there any tool you can recommend to me for meshing CAD data and adding bc's?

Thanks,
Hendrik

  • From: Gothenburg, Sweden
  • Registered: 08-09-2009
  • Posts: 1,419

Re: nodes and elements

Unfortunately, no dedicated preprocessor exists for OOFEM. I generate my input files using a MATLAB script (no CAD geometries)
There are conversion scripts for Salome that you could try out (unv2oofem), or perhaps T3D (free for noncommercial: http://ksm.fsv.cvut.cz/~dr/dr.html )