Normal modes analysis with FASTCONT

Mat_80
Mat_80 Altair Community Member
edited October 2020 in Community Q&A

Hello everybody, I do a 'normal mode' analysis in a model without contact and I get 8 rigid displacements. Then I create the contact surface (with type Freeze) and I active the FASTCON card. So I do again the normal mode analysis but I obtain only 7 rigid displacements. Someone can help me? 

Thank so much for the help 

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Answers

  • FaroukM
    FaroukM Altair Community Member
    edited August 2019

    I don't think that you have something weird .... it seems logical your results ! 

     

  • Mat_80
    Mat_80 Altair Community Member
    edited August 2019

     

     I'm sorry but I'm not really knowledgeable with the program... Can you please explain me the reason why it's logical? Thanks in advance

  • FaroukM
    FaroukM Altair Community Member
    edited August 2019

    By using Fast contact you delete the movement of a rigid body. 

     

    Try to run a simulation by imposing BC : for example U_x = U_y = Uz = 0, keep the Fast contact. Normally, you will eliminate all the rigid body movement.  

     

    Cheers, 

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited August 2019

    •Fast Contact is applicable when the only non-linearity in the model is contact. (no friction) CONTACT=SLIDE

    •Non-linear geometry and material are not supported

  • Mat_80
    Mat_80 Altair Community Member
    edited August 2019

    Thanks a lot .... Another question: if I have to do a frequency response analysis i'll you the same setting used for the modal analysis? 

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited August 2019

    What is your end objective from this analysis? 

     

  • Mat_80
    Mat_80 Altair Community Member
    edited August 2019

    I have to do a frequency response analysis of this:

    <?xml version="1.0" encoding="UTF-8"?>span container2.png

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited August 2019

    Please refer below online tutorial using OptiStruct.

  • Mat_80
    Mat_80 Altair Community Member
    edited August 2019

    I'm sorry to bother you again ... I've downloaded the book but I can't find what I'm searching for. I'll try to reformulate the question: I've done a modal analysis with the card FASTCON in order to linearize the contacts, with property type SLIDE as you suggested and the result was good. Now I'm doing an indirect frequency response analysis: for the contacts I'm turned to used, in property type, SLIDE. Is it correct in this case?  
    Thanks in Advance

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited August 2019

    FASTCONT was developed only for nonlinear analysis.You cannot implement FASTCONT for FRF analysis.

    You can perform FRF analysis for above shared structure.

  • Mat_80
    Mat_80 Altair Community Member
    edited August 2019

    Thank you, I understand. The problem is that we have initially a task to do a linear analysis and a FRF of that cart. After a review they told us to use that card (FASTCONT) for penetrations problems so as to make a more accurate analysis. Then for the linear there were no problems, for the modal, as we have said, we use type=SLIDE. The last thing we have left to do is the FRF. So like you said then we have to delete the surface contact and disable the FASTCONT card and make a FRS with a linear model without contact ? Is it correct in this way?

  • Mat_80
    Mat_80 Altair Community Member
    edited August 2019

    Initially the linear analysis and FRF were without contact**

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited October 2020

    Please refer below post.

    https://community.altair.com/community?id=community_question&sys_id=7f66c03a1b2bd0908017dc61ec4bcb7e

     

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