Non-linear deformed model export

[robXDT2C]

Hi All,

I'm trying to export the deformed shape of a Nastran InCAD non-linear static analysis into .stl format. Some assistance is required regarding if this is possible, and, if it's possible, what is the best method of converting the .bdf results into .stl format.

The first step is to include the TRSLDFGMDATA & TRSLMODLDATA model parameters before solving. The deformed model data should be output into a .bdf file in the FEA subfolder.

The second step is to isolate the deformed model data in the .bdf file. For a linear static analysis the grid data is proceeded by the following:

$ OUTPUT PRODUCED BY ADS NASTRAN VERSION 15.0.0.187 21:58 04/21/20
$
$ DEFORMED GEOMETRY OUTPUT FOR MODE = 1 SCALE FACTOR = 1.0

For a non-linear static analysis, the .bdf format output does not contain a simple "deformed geometry" section. How do I isolate deformed data in the file, particularly if my output contains multiple increment outputs? 

The third step, assuming the linear or non-linear deformed shape is now readable by some software, how do i go about converting it into .stl format? I'm hoping that i've missed a simple solution, as all i can think of is a custom program that would convert grid data into an ASCII .stl file. Unfortunately I am not that good at programming.

The grid data is shown in this format:
$-------2-------3-------4-------5-------6-------7-------8-------9-------0-------
GRID* 1 0 3.5465527717440 0.6264522747967
* -16.xxx-xxxxxxxx 0

ASCII .stl data is normally shown in this format:
solid ASCII
  facet normal 1.462316e-01 9.558480e-01 2.548938e-01
   outer loop
    vertex -2.077858e+01 2.589781e+00 -1.254665e+01
    vertex -2.071004e+01 2.600000e+00 -1.262430e+01
    vertex -2.079127e+01 2.603341e+00 -1.259022e+01
   endloop
 endfacet

If there are any existing tutorials that i've missed, please let me know. If not, i'm hoping someone somewhere has solved this problem.

Thank you for your help in advance!

[lucmartzz]

@robXDT2C did you solved the problem? I'm facing the same problem.

Best Regards

E.M.

[John_Holtz]

FYI. A Google search finds a number of programs that will convert a Nastran file to an STL file. I have not used any of them. The important question is whether these programs automatically find the "outside skin" of a solid and only convert the outside skin (which is what you want for an STL file), or do they convert all of the faces for all of the elements (not what you want). If these programs do the entire mesh, you can try adding a skin of shell elements to the model, and then have the program convert the shell elements to STL instead of the entire model.

Once you find a Nastran-to-STL program that works for your needs, you just need the undeformed Nastran file (which you have) or the Nastran file with the deformation. As the original post indicated, the nonlinear analysis may not output the deformed coordinates of the nodes. In this case, you can use FNO Reader to perform the following operations:

1. Output the GRID commands from the Nastran file to a text file (such as CSV). This gives the original coordinates of the nodes.
2. Output the displacement results from the nonlinear analysis for the load step of interest (such as the last step).
3. Use a spreadsheet to add the displacement results to the original coordinates. This gives the deformed coordinates.
4. Use FNO Reader to write the deformed coordinates back to the Nastran format.
5. Replace the original GRID cards with the modified GRID cards. This creates the Nastran file with the deformation.