Parts with free DOF "grow" in Result of Analysis

Timo Ksr
Timo Ksr Altair Community Member
edited October 2020 in Community Q&A

Hi, 

 

I have a model with certain parts with a free degree of freedom (rotational, actually ball bearings).

 

In the static analysis it happens, that the part 'grows', which obviously is wrong, and I believe the reason is that it is not constraint for every dof. 

 

How can I fix this and still keep the dof6 unconstrained? 

 

Thank you all!

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Answers

  • Q.Nguyen-Dai
    Q.Nguyen-Dai Altair Community Member
    edited July 2020

    Some pictures?

     

  • Timo Ksr
    Timo Ksr Altair Community Member
    edited July 2020

     

    The shaft grows, it has a rotational dof. It is connected to the middle part with RBE2 and CBUSH which connects the rbe2 spiders, which has a K6 = 0 Stiffness.

     

     

    2045120588_shaftsmall.JPG.ed64ab572e17cca1a74a6874c06fb4d5.JPG1261124462_Shaftbig.JPG.5009f24f5d14a19aad32a635bc4bd717.JPG

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited July 2020

    you have to check how much of rotation you get and if this makes sense for your model and analysis type.

    If the large rotations are really expected, HV in static mode doesn't 'understand' rotations too large, and it shows the rotational displacement as if it was expanding.

    You can take a look at transient mode animation to see the proper model rotating.

    If this model is explicit, it is ok to let it free to rotate, and you just need to use 'Transient' animation. 

    If it is implicit, I would make sure this rotations are controlled.

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