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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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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.

spring mass damper.fem

EIGVSAVE and EIGRETRIEVE.JPG

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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.

 

 

 

 

 

 

plot-eigenvectors.JPG

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On 28/2/2018 at 11:32 PM, Rahul R 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.

 

 

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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

Eigenvector in punch.JPG

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29 minutes ago, Rahul R 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

Eigenvector in punch.JPG

Thank you Rahul, 

 

This is exactly what I was looking for!

 

Rahul R likes this

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