Plot eigenvectors

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

Hi all,

 

How can I plot the eigenvectors of a mass-spring system?  

 

I have a system like this:   constraint ----spring-----mass-----spring-----mass-----spring-----constraint

A 2 degrees of freedom system, in a modal analysis will output 2 eigenvectors. I would like to see the vectors in the output file along with the eigenvalues (it is only for educational purposes). How can I do it?

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Answers

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

    Please refer attached fem for spring mass 1dof. You can export eigen value and eigen vector individually using HV query panel.

    But if you want to consider the effect of modal analysis for Modal frf case then EIGVSAVE and EIGRETRIEVE option listed in subcase section would help you.

    Check OptiStruct user guide for the detailed information.

    <?xml version="1.0" encoding="UTF-8"?>EIGVSAVE and EIGRETRIEVE.JPG

    Unable to find an attachment - read this blog

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited February 2018

    Hi Raul,

     

    Thank you for the answer.

    I can't dowload the .fem you uploaded (I don't know why) but I would like to do something like in the picture that I am attaching (I took it from an old Nastran output).

    I want to see if my hand calculations are right on a few dof system.

     

     

     

     

     

     

    <?xml version="1.0" encoding="UTF-8"?>plot-eigenvectors.JPG

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited February 2018

    Could you please share the solver input file for better understanding of inputs defined and output requested for above screenshot model?

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited March 2018
    Altair Forum User said:

    Could you please share the solver input file for better understanding of inputs defined and output requested for above screenshot model?

     

    Hi Rahul,

     

    Sorry, I saw your reply to my question only few days ago. I don't have the input file relating to the picture because I took it from a document. I would like to plot the eigenvectors, like in the picture above, using Optistruct (it would be great if it appeared in the .out file). I need the results only for 'educational' purposes. If it wasn't possible I could obtain the same results using Hyperview, measuring the response of the modal analysis node by node, but honestly I hope there is a better way to do it.

     

     

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited March 2018

    One of my colleague suggested to extract output in punch format. This should fetch result in expected format.PFA screenshot for your reference.

    Control cards:Output:Set keyword to punch and set Freq to all

    <?xml version="1.0" encoding="UTF-8"?>Eigenvector in punch.JPG

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited March 2018
    Altair Forum User said:

    One of my colleague suggested to extract output in punch format. This should fetch result in expected format.PFA screenshot for your reference.

    Control cards:Output:Set keyword to punch and set Freq to all

    <?xml version="1.0" encoding="UTF-8"?>Eigenvector in punch.JPG

    Thank you Rahul, 

     

    This is exactly what I was looking for!

     

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