Introduction
This tutorial for a model with 2 tubes in contact is a simple example of how to utilise ‘Physical Groups’ in the open source meshing tool Gmsh [1] to create node and element groups for OpenRadioss that may be used to define e.g. boundary conditions or initial conditions, at the time of writing (June 2023) the functionality is available only in the ‘development build’ of Gmsh
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The model geometry is provided as a Gmsh ‘.geo’ file
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Model Files
The model files include the OpenRadioss Engine file (Tube_Impact_0001.rad), and a Gmsh .geo geometry file (Tube_Impact.geo) for the tubes.
Step 1: Define ‘Physical Groups’ in Gmsh
The files for this example include an example Gmsh .geo geometry file,
To use Gmsh to set the model up, you may follow the steps below
1.1: Download the ‘development’ release of Gmsh binary and extract
1.2: Open gmsh.exe (windows) or run gmsh executable in Linux
1.3: From File Menu, open the Tube_Impact.geo file
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1.4: Create Physical Curve Groups
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After the 2 groups have been created, you may press 'q' to exit the group creation tool
1.5: (Optional) Create Physical Surface Groups
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Similar to the creation of the curve groups, this time create a group named ‘Top_Tube_Elements’ and select the surface of the top tube, then a group named ‘Bottom_Tube_Elements’ and select the surface of the bottom tube
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1.6: expand the Mesh option in the menu, then click ‘2D’
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The mesh can now be exported,
1.7: go to File → Export, save as type ‘RADIOSS BLOCK’ into the folder where your model files are saved and use the filename Tube_Impact_0000.rad matching the naming of the supplied engine file (0001.rad)
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| Info |
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NB: Physical Groups: When ‘Physical Groups’ have been defined in Gmsh, the export panel uses them in the following ways: If ‘Physical Groups’ are chosen in the Line, Surface, Volume option boxes then only entities (nodes/elements) associated with those groups will be exported in their part groups (it acts as on a filter on what is to be exported) If the Options ‘Save groups of elements’, ‘Save groups of nodes’ are checked, then the element and/or node groups defined will be exported. (The group exporting works independently of the actual node and element export, so you could export the group alone if you wished) |
Step 2: Adding Part, Property, Material and Interfaces to the Deck
The file exported from Gmsh contains file header, elements, nodes and element and node groups, but needs to be edited to add Material, Property, Boundary Condition and Contact Information
2.1: Open the _0000.rad file in a text editor:
Edit the name of the model (line after /BEGIN) if necessary, (windows Gmsh may write whole file path here depending on where the file was written) it should read Tube_Impact
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2.2: Create Material, Property and Part Cards
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| Code Block | ||
|---|---|---|
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#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/PART/2000001
Bottom_Tube
1 1 0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/PART/2000002
Top_Tube
1 1 0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----| |
2.3: Define /BCS boundary conditions using the groups exported by Gmsh
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| Code Block | ||
|---|---|---|
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#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----| /BCS/1 Moving # Tra rot skew_ID grnod_ID 110 000 0 1 #---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----| /BCS/2 Fixed # Tra rot skew_ID grnod_ID 111 000 0 2 #---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----| |
2.4: Define a Part based node group for use in initial velocity definition and an INIVEL card
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| Code Block | ||
|---|---|---|
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#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/GRNOD/PART/100
Top_Tube
2000002
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/INIVEL/TRA/1
20m/s
# Vx Vy Vz Gnod_id Skew_id
0 0 -20000 100 0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----| |
2.5: Define a surface for contact based on parts and a contact
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| Code Block | ||
|---|---|---|
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#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/SURF/PART/1000
For Tube Contact
2000001 2000002
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/INTER/TYPE25/1
Contact
# Surf_ID1 Surf_ID2 Istf Ithe Igap Irem_i2 Idel Iedge
1000 0 0 0 0 0 0 0
# grnd_IDS Gap_scale %mesh_size Gap_max_s Gap_max_m
0 0 0 0 0
# Stmin Stmax Igap0 Ishape Edge_angle
0 0 0 0 0
# Stfac Fric Tpressfit Tstart Tstop
0 .3 0 0 0
# IBC IVIS2 Inacti ViscS Ithick Pmax
000 0 0 0 0 1E30
# Ifric Ifiltr Xfreq sens_ID fric_ID
0 0 0 0 0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----| |
ALTERNATIVE OPTIONAL: 2.5:
If you want instead to use the element sets created in Gmsh to define a symmetric SURF-SURF contact (where the tubes contact each other, but not themselves)
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| Info |
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If you experiment with different meshing in Gmsh, resulting in quadrilateral shell elements instead of trias, then the steps above remain the same but the groups will be of type /GRSHEL/SHEL and /SURF/GRSHEL |
Step 3: Running Model in OpenRadioss
The model file Tube_Impact_0000.rad can be run in OpenRadioss, the Tube_Impact_0001.rad engine file contains output requests for displacement, velocity and von mises stress
See also: Running OpenRadioss
Viewing Results
The engine file _0001.rad as contained in the zip requests animation files (Annn) these are convertable to vtk for reading in ParaView. Check the Pre and Post Processing for OpenRadioss page for information.
References
1: Gmsh (C. Geuzaine and J.-F. Remacle. Gmsh: a three-dimensional finite element mesh generator with built-in pre- and post-processing facilities. International Journal for Numerical Methods in Engineering 79(11), pp. 1309-1331, 2009)2: Steel Material Data from SSAB: SSAB – a stronger, lighter, and more sustainable world