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  1. stefanix1972

    Nastran random response analysis on a free-free structure

    Dear DG, thanks for the reply, maybe my question was not well posed and I'm not sure to fully understand the answer. The disturb in my structure is in a whatsoever node and can be of different nature. It can be for example a PSD of acceleration g²/Hz or a of a force (N²/Hz). Or it can be in the...
  2. stefanix1972

    Nastran random response analysis on a free-free structure

    Dear all, I'm investigating the response to a disturb of a spacecraft in flight. The disturb can be thought as a random acceleration input applied to a node (as a PSD, for example). My approach would be to use SOL111, DLOAD and RANDPS, but the point is that structure is a free-free one...
  3. stefanix1972

    Modal Participation Factor Meaning in Nastran

    Dear all, I just came across in this thread because I'm interested in calculating the modal effective mass of a portion of my structure. In Altair Optistruct MEFFMASS command is "cloned" and improved: MEFFMASS(COMP,PROP,SET=1001,SUMMARY,PARTFAC,HG,OPTI)=YES it is possible to define a set of...
  4. stefanix1972

    MONPNT3 output in pch rather than in f06

    Hi DMAPguru, thanks for the suggestion, but I think it is another intermediate step. At this point, I think I'll go for an Excel macro (or a spreadsheet) that imports f06 results and procuces a pch. I'll keep updated the community. Regards, stefanix1972.
  5. stefanix1972

    MONPNT3 output in pch rather than in f06

    Hi SWComposite, in my company we use a tool that postprocess Nastran sine analyses and also can import test results. It imports several type of files, one of them is pch file. Currently we use MPCs to get accelerations in specific items CoGs, but MPC creation is cumbersome, whereas MONPNT3 is...
  6. stefanix1972

    MONPNT3 output in pch rather than in f06

    I asked to MSC technical support and they confirmed me that there is no internal command or specific alter to generate a pch file with data provided by MONITOR instruction.
  7. stefanix1972

    MONPNT3 output in pch rather than in f06

    Dear Community, as pointed out in thread825-467136 I see that MONPNT3 can sum selected grid point forces to a user chosen monitor point. This can be done by MONITOR case control section instruction. Unfortunately, results are provided in f06 file but not in a pch file, that would be much better...
  8. stefanix1972

    Assessing Random Load with Yield Strength?

    Dear Sarclee, you are right: in space industry random vibration is relevant in the 120 seconds from launch onwards, so there is no real concern for fatigue due to random vibration. There is a minor concern for fatigue for the effects of ground tests, transportation loads, launch loads. Thermal...
  9. stefanix1972

    Assessing Random Load with Yield Strength?

    Dear Sarclee, by random analysis, if you input nominal PSD (e.g. in acceleration expressed in m/sec2) you get the RMSstress value in N/m2. This RMSstress value has to be multiplied by three: MoS = Yield/ (SF*3*RMSstress) - 1 In synthesis, be careful not to multiply twice by three. You also...
  10. stefanix1972

    Assessing Random Load with Yield Strength?

    Dear Sarclee, in random vibration you get RMS stress plot from analysis (e.g. by Patran Random utility, that postprocesses Nastran SOL111 FRF). Maximum RMS stress value has to be multiplied by 3 to get the so called 3 sigma value. In this way you are confident that in 99.7 % of cases that stress...
  11. stefanix1972

    Spacecraft transient dynamic analysis with SOL400

    Dear all, I'm trying to analyze a spacecraft manouevre around its CoG by Nastran 2019 SOL400 transient dynamic analysis. Preliminarly, I checked with a small model what the best solution could be, and I found other SOLs giving problems: SOL109 direct transient gives "inflated" deformed shape...

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