Nastran op4 & pch modification

[Mrkvel]

Hi,

I was assigned with a task to prepare a FEM for a CLA analysis (coupled loads analysis). The process should consist of standard nastran superelement reduction resulting in OP4/PCH/ASM file.
I should deliver the matrices separated (stiffness, mass, OTM forces, OTM accelerations, OTM displacements...). I also need to remove certain degrees of freedom from the matrices (for example rotational DOFs for displacements/accelerations). I was able to do so by using a python library pyYeti on the op4 files.
For example if I remove the DOF3 (z-acceleration) by modifying the MUG1 op4 matrix I need to modify the TUG1 partitioning table in the pch as well and that's where I'm lost. I tried to modify the first DTI TUG1 entry to account for the removed DOFs by stating the matrix size of 28x27 (instead of 30x27) and then modifying the second DTI TUG1 entry for COMP and ROW columns but either the analysis crashes or the results get mixed up/shifted - the AX result becomes AY etc.

Anybody here familiar with such modifications/CLA preparations?

 

[jamesdean2]

Hi Mrkvel,
I've submitted several CLA packages using pyYeti, but most of the work is done in pandas.
My submittals consist of:
1. An Excel file with the LTM, ATM, & DTM.
2. The partitioned op4 file that contains stiffness and mass matrices as well as acceleration, displacement, and loads transformation matrices that are reduced to only containing the NASTRAN set card request and Excel file.
3. The ASM file from the original CMS run.
4. Documentation of the model checks.
So a PCH file is not part of the package, that said it's super important that the relationship between the TUG1 and MUG1 be maintained. I do that by identifying the columns in both matrices and intersecting those matrices with a subset of desired responses(Excel file). Using Pandas makes it simple to maintain this alignment without using any looping.
Recommend you go through the 'readthedocs' for pyYeti, and familiarize yourself with pandas. Typically, I only check the CB model as the original superelement and then again using the cbcheck module within pyYeti. Hope this helps.

 

[Mrkvel]

Hi jamesdean2,

thanks for the response, I really appreciate it as it's hard to find any kind of information regarding this topic online.

I'm delivering the CLA package to Arianespace. The usual delivery consists of:

- separate op4 files with AC01, DP01, LTM1, LTM2, stiffness and mass matrices (1 op4 file per each) - I can separate the files with pyYeti
- xban file which I guess is something like your excel file (it contains the definition of the restitutions and has a simple structure)
- something like a combined asm and pch - it has spoint definition and then DMIG partitioning vectors - this is where I'm stuck

Do you supply the excel with the partitioning vectors to your launcher authority or how do you define/communicate the relationship between the TUG1-MUG1?

 

[jamesdean2]

 

[jamesdean2]

Hi Martin, I've sent you some Python pointers on how to manipulate the NASTRAN data.