Error with shell elements: a minimal example

1

Hi,
I am a CFD & finite volume guy, and a new CalculiX user (and new to FEM in general). My problem will probably sound very silly, but I couldn’t manage to solve it, so I’d appreciate any help.
I am trying to understand the structure of a CalculiX case on this simplest possible case:

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Here is my job.inp file

*INCLUDE, INPUT=mesh.inp

*MATERIAL, NAME=steel
*ELASTIC
210e9, 0.3
*DENSITY
7850

*SHELL SECTION, ELSET=plate, MATERIAL=steel, OFFSET=0
0.01

*STEP
*STATIC

** Fix the root (all displacements = 0)
*BOUNDARY
fix, 1, 3

*DLOAD
plate,GRAV,9.81,0.,-1.,0

*END STEP

and my mesh.inp file:

*Heading
test
*NODE
1, 0, 0, 0
3, 1, 0, 0
4, 0, 0, 0.5
6, 1, 0, 0.5
7, 0, 0, 1
9, 1, 0, 1
2, 0.5, 0, 0
8, 0.5, 0, 1
5, 0.5, 0, 0.5
******* E L E M E N T S *************
*ELEMENT, type=T3D2, ELSET=Line2
5, 3, 6
6, 6, 9
7, 4, 1
8, 7, 4
*ELEMENT, type=T3D2, ELSET=Line3
9, 1, 2
10, 2, 3
*ELEMENT, type=T3D2, ELSET=Line4
11, 9, 8
12, 8, 7
*ELEMENT, type=S4, ELSET=plate
1, 1, 2, 5, 4
2, 2, 3, 6, 5
3, 4, 5, 8, 7
4, 5, 6, 9, 8
*ELSET,ELSET=Unspecified
5, 6, 7, 8, 
*ELSET,ELSET=fix
9, 10, 
*ELSET,ELSET=load
11, 12, 
*ELSET,ELSET=plate
1, 2, 3, 4, 
*NSET,NSET=Unspecified
1, 3, 4, 6, 7, 9, 
*NSET,NSET=fix
1, 2, 3, 
*NSET,NSET=load
7, 8, 9, 
*NSET,NSET=plate
1, 2, 3, 4, 5, 6, 7, 8, 9,

And this is the output I get:

You are using an executable made on So 31. Jul 13:26:31 CEST 2016

  The numbers below are estimated upper bounds

  number of:

   nodes:          697
   elements:           12
   one-dimensional elements:            8
   two-dimensional elements:            4
   integration points per element:            8
   degrees of freedom per node:            3
   layers per element:            2

   distributed facial loads:            0
   distributed volumetric loads:            1
   concentrated loads:            0
   single point constraints:          945
   multiple point constraints:         1441
   terms in all multiple point constraints:         9217
   tie constraints:            0
   dependent nodes tied by cyclic constraints:            0
   dependent nodes in pre-tension constraints:            0

   sets:           12
   terms in all sets:           54

   materials:            1
   constants per material and temperature:            2
   temperature points per material:            1
   plastic data points per material:            0

   orientations:            0
   amplitudes:            2
   data points in all amplitudes:            2
   print requests:            0
   transformations:            0
   property cards:            0

 *ERROR in gen3delem: first thickness
        in node            1  of element            5
        is zero

I checked the tutorials (and ChatGPT also), but still can’t pinpoint the problem. CCX complains about zero thickness, despite I define it.

My mesh generation process: Create mesh in Pointwise (2D, solver: Gmsh) > Export to Gmsh v2 format (.msh) > Open in Gmsh > Export to .inp format > Make final modifications in the file.

Thanks in advance.

1 Like
2

@hconel , you’re missing cross-section specification for elements line2,line3 and line4

if you add the following lines in your data-set you will get a result

*SOLID SECTION,ELSET=Line2,MATERIAL=steel
.025
*SOLID SECTION,ELSET=Line3,MATERIAL=steel
.025
*SOLID SECTION,ELSET=Line4,MATERIAL=steel
.025
3

Dear @fgr,
Thanks for your answer.
I noticed that although I do not want those line elements to be included in my .msh and .inp files, PointWise and Gmsh prints them anyway. I also noticed that deleting those type=T3D2 elements from the .inp file does not affect my simulation, and moreover, clears the error, leading to a successful simulation.
Now I wonder, instead of deleting those manually, is there anything I can do in the CalculiX .inp file to set such elements “not to be simulated”, or void, ignore, something like that?

4

export mesh from gmsh using Physical Groups, have a look at in gmsh website/manual

However we recommend to start as a new user with the graphical pre/post Prepomax (windows only): https://prepomax.fs.um.si/downloads/

5

Hi @JuanP74,
I have to work on Linux, so unfortunately I can not use PrePoMax…