Modal effective masses and pyNastran

[Corentin Blanchard]

Hello everybody,

I am working on a project for which I have to monitor the modal effective masses of a model. I am especially interested in the fraction of the total mass carried by the real eigenmodes (SOL 103).

In the bdf file, the MEFFMASS case control command is defined as such: MEFFMASS(PRINT,SUMMARY,MEFFM,FRACSUM) = YES.

The analysis runs well and op2 and f06 files are written. In the f06 file, there is the MODAL EFFECTIVE MASS FRACTION section which to me confirms that the case control command has worked. I then post-process the op2 file it with :

from pyNastran.op2.op2 import OP2

model = OP2()
model.read_op2(op2_filename)

But when I inspect the model object with model.get_op2_stats(), I only see the eigenvectors attribute. In addition, model.matrices returns an empty dict. This makes me believe that the results I am looking for are not present.

I would like to know if such situation comes from the definition of the MEFFMASS case control command (wrong/incomplete describers definition for instance?) or if I have to do something specific with pyNastran to access the results.

In the documentation, I also saw the OP2_Scalar class that seems to handle some modal effective matrices, but I didn't figure out how to run it.

Any help to better understand the situation would be greatly appreciated. By then, congratulations for the tool! I might use 5% of it, but so far it has done exactly what I wanted in a very simple way!

Corentin.

[Corentin Blanchard]

Hello everybody, quick followup regarding this topic.

According to the NX NASTRAN Quick Reference Guide, it is possible to replace PRINT by PLOT to write the modal effective mass results in an op2 file. However, I use MSC NASTRAN. I have tried to use PLOT but the run results in an USER FATAL MESSAGE 601 (IFP1D) saying that "THE KEYWORD ON THE ABOVE CARD TYPE IS ILLEGAL OR MISSPELLED.". In other words, PLOT is not accepted and I am still stuck.

Once again, any help would be greatly appreaciated. Thank you very much in advance!

Corentin.

[Ankush Shenoy]

Were you able to find a solution to this?

[Steven Doyle]

I just ran a test in NX and it’s working fine. It should show up in the matrices. I don’t remember that message, but it’s seems MSC specific. I want to say I added the functionality 10+ years ago.

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[Ankush Shenoy]

Yes I think it's an MSC issue. The matrices output seems to be empty when I print it. I am extracting it from the f06 file for now. 

Ankush Shenoy

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