NX .sim files store absolute internal references to .fem/.prt files.
Copying them to iteration folders breaks these references (Parts.Open
returns None). Instead:
1. Backup master model once at study start
2. Restore from backup before each trial (isolation)
3. Solve on master model in-place (NX references intact)
4. Archive solver outputs (OP2/F06) + params.exp to iterations/iterNNN/
5. params.exp in each iteration: import into NX to recreate any trial
iteration_manager.py kept for future use but not wired in.
Antoine
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