Interpretation of Free-Free Modal Participation

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

We are running a vehicle shell model with additional lumped masses where needed attached to the shell structure.  We achieve reasonable results, 6 rigid body modes followed by 20 modes that align with our other software tools.  There is some discrepancy and we are not clear on whether displacement of the cg is occurring in modes 7-20.  In the  .pch file we are able to see the displacement of the mass elements as a result of each mode.  Are those values real displacements, both positive and negative in a coordinate direction, or is there an imaginary component to the displacement?  Is there a was to determine the motion of the CG of the system for each mode?

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Answers

  • FaroukM
    FaroukM Altair Community Member
    edited September 2020
    Altair Forum User said:

    Are those values real displacements,

    When we perform a free-free modal analysis, the obtained results are normalized. Which means the displacement is not the real one. It represents the shape of the mode.

     

     

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

    Not only free-free modal analysis, but in any modal analysis, the results are always normalized, either by displacement or by mass.

  • FaroukM
    FaroukM Altair Community Member
    edited September 2020
    Altair Forum User said:

    Not only free-free modal analysis, but in any modal analysis, the results are always normalized, either by displacement or by mass.

    Yes :)/emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' /> but he specified free-free modal analysis :)/emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' /> ! 

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