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.
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 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.
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)
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.