Jump to content


  • Content Count

  • Joined

Reputation Activity

  1. Rex liked a post in a topic by Rahul R in PSD analysis   
    You can refer to below Altair Resource Library with keyword as random.
  2. Crashphys liked a post in a topic by Rex in Punch File Format for Ply Stress Outputs   
    I also faced similar problem, but I just fixed, I know what is the problem you want to solve! In Optistruct help document, the format for the stress outputs is not given, so we will confuse with all these stress tensors, it also took me long time to understand the stress tensor during FRF simulation, below is my solution.
    1) First of all,  you need have the .pch file for desired element, all the stress tensors is shown in it, I already saw it in you picture
    2) Then you can load the .h3d file in Hyperview,  and hide all the element except the desired element.
    3) Now you can plot the stress of this element (please keep the averaging method as none),  then compare this contour plot result with your .pch file, by using this way you can understand the format of the stress tensors
    Hope this can help u!
  3. Rex liked a post in a topic by Rahul R in Eigenvalue of fluid   
    Please refer attached MFLUID example in OptiStruct.
    MFLUID.pdf MFLUID_Example.zip
  4. Rex liked a post in a topic by Rahul R in PSD fatigue model chekcing   
    Please make sure to keep the unit consistent. Refer the below post where we shared best practices for random response analysis.
    Some Tips for results comparison with other solver
    • Use “Amplitude” in MATFAT (default is “range” in OS)
    • Request for “Damage” results on elements in other solvers
    • Define right option for PSD input  for random vibration fatigue (Log vs linear) 
    Attached Random Fatigue deck for your reference.
    Note: OptiStruct supports Random Fatigue Analysis only Uniaxial SN with Von-Mises stress and approximated principal stress
  5. Farouk Maaboudallah liked a post in a topic by Rex in Fatigue simulation in frequency domain   
    1) ASD is Acceleration spectrum density, it always with the unit (G^2/Hz) in X direction and Hz in X direction, and it tells how much the acceleration will be in 1sigma level.
    2) If you want to know why I want to run the random fatigue in frequency domain, you can search on google, they explain it better than me. For me, I would say do the random fatigue in time history is a very time-consuming work, and usually if you want to know the random input in a better way, you need enough acceleration data in time domain. Meanwhile, if you see the acceleration input on time history, sometime it does not help you too much, but in the frequency you could find which frequency is more important.... oh, by the way,by using Miner rules, we can even get the total damage considering different acceleration inputs(like the acceleration on the air intake manifold can be caused by engine and road together, it's difficult for us to consider the fatigue in time history...)
    Please learn more on this topic by using google or here, all these answers are based on my understanding, if I am wrong, just let me know!
  6. Rex liked a post in a topic by Rahul R in PSD analysis setup in Optistruct   
    You can refer the model shared in below post.
    So, you define the excitation (SPCD / Force) in the FRF step. For example if you want to apply SPCD in X, Y and Z directions, you will have
    1. 3 number of Subcases with 3 DLOAD

    2. 3 RLOAD cards corresponding to DLOADs

    3. 3 SPCD cards

    4. one or more TABLED1 card
    Now, the loading will be applied in FRF step and the results are outputted for those loads.
    When it comes to Random part, you need to define Random Input for all 3 direction using same ID. 'All RANDPS entry with same ID will be added together'.
    RANDPS,101, 11, 11, 1.0, 0.0, 11

    RANDPS,101, 12, 12, 1.0, 0.0, 12

    RANDPS,101, 13, 13, 1.0, 0.0, 13
    With 3 TABRND1 cards ( 11,12 and 13)
    The additive results of Random are then multiplied to the FRF results to get PSD / RMS outputs.

    Hja and Hjb are the results from FRF and Sab from Random (PSD)

     Please refer attached to pdf for the two scenarios based on Random input.

    Random Input.pdf
  • Create New...