Model runs for analysis but not for optimization

Stéphane C.
Stéphane C. New Altair Community Member
edited October 2021 in Community Q&A

Hello,

I try to run  an optimization run (see file attached).

When running analysis it's okay, but when running optimization I have the message

The rotational displacement has large magnitude, -178164 degrees

At beginning of .out of optimization I have this information:

*** INFORMATION # 815
 The total number of rigid elements, whose rotational dependent d.o.f.
 are removed because there is no need to constrain those d.o.f., is 3.

 I don't understand if my optimization error is coming from this automatic removal or from something else?

Thank you very much!

Stéphane.

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Answers

  • Robert Hoglund
    Robert Hoglund
    Altair Employee
    edited October 2021

    Hi Stephane,

    I believe the message happened because the RBE2 is only constrained in DOF 123 in both locations.  So, the model is freely rotating about the axis between the two constraints when the load is applied as there is no DOF fixed in rotation.

    The rotational dependent DOF message is occurring because the RBE2s are connected to solid elements which don't have rotational DOFs to constrain.  Making the switch to constrain DOFs 456 is one way to allow the optimization to run- I'll attach the fem model.

    image

    Thanks,

    Rob H.

  • Stéphane C.
    Stéphane C. New Altair Community Member
    edited October 2021

    Ok beginner mistake!

    So I guess Optistruct creates autospc for linear static solving, but don't do it for optimization solving.

    Thnak you very much!

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