2.8 THE
COSMOS CONVERTER Z88G
Sometimes 3D CAD programs
include so-called automeshers which devide a CAD model into finite elements. This
generated mesh can be stored in some output format to fit the needs of the
various FEA programs.
Typical output formats are
the COSMOS and the NASTRAN format for the COSMOS or the NASTRAN
FEA program.
Z88G is developed and tested for Pro/ENGINEER
by Parametric Technology. USA. Pro/ENGINEER must include the option Pro/MECHANICA.
Be sure to define the material data (e.g. for steel, only Young's Modulus and
Poisson's Ratio is really needed) in Pro/ENGINEER.
Then you may activate FEM in
the Pro/ENGINEER program after designing your 3D model , define a coordinate
system (which must be in harmony with Z88 !) and add forces and boundary
conditions to single points. Create these single points with Feature >
Datum > Point. For plates the direct entry of the pressure load is
allowed. When using Wildfire 2, do
not forget to define an analysis. Otherwise, no boundary conditions are filed!
Modify the mesh control
values, if necessary. Create the mesh with Make Model and choose the
element type e.g. Tet Mesh or Shell Mesh. Store the mesh with Output
Model, choose NASTRAN or COSMOS/M and linear or parabolic.
Enter z88g.nas for NASTRAN files or z88g.cos for COSMOS files for
the output file name.
Then lauch the converter Z88G.
The converter produces the Z88 input files Z88I1.TXT, Z88I2.TXT and Z88I3.TXT and Z88I5.TXT
(if needed) automatically. You may then enter the Z88 input files and edit
values e.g. material data and integration orders, if necessary.
Test the Z88 input files
generated by Z88G with the filechecker Z88V. Plot Z88I1.TXT with the plot program Z88O or Z88P. If you find a 3D model totally flat: You've
defined a coordinate system CS0 in Pro/ENGINEER which does not fit Z88's needs.
Simply define a new correct coordinate system in Pro/ENGINEER and define it as
datum when outputting the model.
Keep in mind that those exchange
file formats and their Pro/ENGINEER output are subject to change every some
months. Visit www.z88.de or www.z88.org for updated versions of Z88G.
You may create the
following Z88 element types with Z88G:
Tetrahedron
No.16 (Tetrahedron,
parabolic in Pro/ENGINEER)
Tetrahedron
No.17 (Tetrahedron,
linear in Pro/ENGINEER)
Plane
stress No.14 (Shell,
triangle, parabolic in Pro/ENGINEER)
Plane
stress No.7 (Shell,quadrangle,
parabolic in Pro/ENGINEER)
Plate
No.18 (Shell,
triangle, parabolic in Pro/ENGINEER)
Plate
No.20 (Shell,quadrangle,
parabolic in Pro/ENGINEER)
Torus
No.15 (Shell,
triangle, parabolic in Pro/ENGINEER)
Torus
No.8 (Shell,quadrangle,
parabolic in Pro/ENGINEER)
How to proceed?
First step: Choose NASTRAN
or COSMOS file format: If you choose NASTRAN the file Z88G.NAS is loaded, in
case of COSMOS the file Z88G.COS is loaded. You must know which file type did
you file in your former Pro/E session.
(Choose file type before
start. The UNIX version of Z88G operates in console mode)
Next step: Pro/ENGINEER
makes no distinction between plane stress elements, torus elements and plate
elements, so, it's up to you to feed Z88G with the right information; choose
the proper element type (the type you prepared in your former Pro/E session) in
Z88G before starting the conversation run:
The generation of volumes
is easy but the generation of plane stress elements, plates and torus elements
is tricky: Firstly, build a volume with (small) thickness in Pro/E. Set
reference points, especially for axisymmetric elements. Launch Pro/MECHANICA
and idealize the volume into shells: Model > Idealizations >
Shells > Midsurfaces. This eliminates the depth. When working with
axisymmetric elements keep in mind that you are working in cylinder
coordinates: Your coordinate system coincidates with the axis of rotation and
the "volume” lies on the corresponding radiuses:
(Here
you see the generation of torus elements in Pro/ENGINEER (Wildfire). Proceed
similar for plane stress and plate elements)
Please
keep in mind: These FEA output data formats, especially the NASTRAN format, are
really monthly modified. However, why should they kept for a while in the same state?
Would be too easy. The COSMOS format is more stable but is missing in Pro/ENGINEER
Wildfire. Thus, if you’re using Pro/E up to version 2001
you should store COSMOS files and starting from Wildfire store NASTRAN
files. If you’ll store NASTRAN files for Pro/E versions up to 2001 you
must check and modify the NASTRAN files: especially material properties are
printed as wrong floating point values e.g. 2.06+5. Change such stuff to
e.g. 2.06E+5 or 206000.
Anyway:
Z88G looks quite harmless, but proper operated Z88G is a mighty tool which
allows you to file very large FEA structures to Z88.