Fixed flag for preload

Yuri S.
Yuri S. Altair Community Member
edited June 2021 in Community Q&A

Hi everybody,

I set up a simple model (a cantilever beam) to figure out how the option "fixed" works in case of preloading.
This option can be flagged within the constraint menu, as shown in the attached picture.

Supposing to be performin a NL static analysis, this option is meant to keep the deformation coming from a generic subcase and use it as preload for the subsequend loadcase (please correct me in case I am wrong).

According to the manual, this option should be very trivial to be used, yet I keep having trubles. Activating this option, causes the imposed deformation in my model to be massively amplified, leading of course to non-convergence. The exact same simulation runs perfectly unchecking the "fixed" flag, yet of course without imposing the deformation of subcase 1 as preload for subcase 2.
I attach the two models I was trying out. 

Does anybody know which should be the correct procedure to use this option?
Any suggestion or comment is welcome.

Have a nice day,
Yuri 

image

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Answers

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited June 2021

    for preload and subsequential, in your 2nd loadcase you could use STATSUB(PRETENS) and turn on CNTNLSUB (continuation from NL subcase), pointing to the previous pretension loadcase.

    If you don't use CNTNLSUB it won't keep the state of the previous LC.

     

  • Yuri S.
    Yuri S. Altair Community Member
    edited June 2021

    Hi @Adriano A. Koga , I have tried you suggestion out but it doesn't seem to work. Perhaps I didn't understand you right. Could you be more specific?

    Besides that, do you have any indication about the correct use of the fixed option?

    Thank you very much

     

    image

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited June 2021
    Yuri S. said:

    Hi @Adriano A. Koga , I have tried you suggestion out but it doesn't seem to work. Perhaps I didn't understand you right. Could you be more specific?

    Besides that, do you have any indication about the correct use of the fixed option?

    Thank you very much

     

    image

    I'm sorry. I thought you meant bolt pretension. My bad.

    If it's just NL sequential loading, forget the STATSUB, and add just the CNTNLSUB as you already did.

     

    Make sure you keep in the 2nd case, all spcs and forces that you want to keep applied from the 1st one.

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