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Eigen Value

9 REPLIES 9
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Message 1 of 10
nitinhadpe
1405 Views, 9 Replies

Eigen Value

Hello All,

I have one question regarding Eigen Value?

Accroding to literature it's critical load factor, means material load acting on part.

If Eigenvalue Lamba is >0 and <1, then part will buckle, in this case aprt from warpage do we need to look it's buckling also.

I want to understand, what's the significance of Eigen value in warp analysis?

Many times i heard from friends that client ask us to give Eigen value, does it really reflect part warpage behaviour.

Regards,
Nitin Hadpe
Neilsoft, Pune, India

Edited by: nitinhadpe on Mar 23, 2010 7:58 AM Edited by: nitinhadpe on Mar 23, 2010 8:17 AM
Regards,
Nitin Hadpe
Neilsoft Ltd, Pune, India
9 REPLIES 9
Message 2 of 10
BobSherman5561
in reply to: nitinhadpe

G'day Nitin,

A positive eigenvalue less than 1.0 indicates that the shrinkage loads when applied to the part geometry cause an instability in the deflection behavior, and the eigenvalue shown is the predicted shape (without magnitudes) that the part will start to assume when the shrinkage values reach the percentage of level associated with that eigenvalue (say 75% for an eigenvalue of +0.75). In order to know how the part will behave beyond 75% of the predicted shrinkages, a large deflection analysis has to be performed and converge properly to better predict how the part will warp.

The eigenvalues are determined by a linear buckling analysis and the true behavior which is only predicted by the large deflection analysis can be different, but are usually very similar. If the eigenvalue is close to 1.0, the deflections in the large deflection analysis may not be too great. But it is important to remember that no software is perfect and such instabilities in warpage need to be avoided with some margin of safety. I would not want to rely on analysis accuracy to conclude that buckling would not occur unless the eigenvalues are at least 1.50.

Hope this helps,
Bob Sherman
Senior CAE Analyst, RTP Company
Message 3 of 10
nitinhadpe
in reply to: nitinhadpe

Hello Bob,

Thanks a lot for your answer.

I still have one small query regarding the same. If you knows the answer, please clarify me. That would be a great help.

1. If we put warpage analysis type - AUTOMATIC then it automatically calculates Eigen value.

If value is less than 1 then it does small scale deflection and if it's greater than 1 then it automatically starts large scale deflection analysis.

Then in this case do we really need to bother for EIGEN VALUE in Warpage analysis?

Regards,
Nitin Hadpe Edited by: nitinhadpe on Mar 29, 2010 12:38 PM
Regards,
Nitin Hadpe
Neilsoft Ltd, Pune, India
Message 4 of 10
BobSherman5561
in reply to: nitinhadpe

G'day Nitin,

In today's versions of Moldflow with the Automatic analysis, it handles everything for you without much user inputs necessary. Previously, these steps had to be performed manually and they still do sometimes if the Automatic analysis fails. Knowing at what level the of shrinkage loads the eigenvalue is at, helps in determining the steps necessary to get a large deflection analysis to converge more easily. If too large of incremental loads steps are used when the instability is approached, the analysis can sometimes jump too far and miss the instability, so yes the eigenvalue is an important piece of knowledge necessary for correct analysis of the large deflections when an instability is present.

It also is helpful to know for the user to determine how drastically the shrinkages need to be altered. If the eigenvalue is 0.5, drastic changes will be needed to get it considerably above the 1.2-1.5 range. Whereas if it is @ 0.9, maybe only key design modifications may be necessary to solve the problem.

Hope this answers your question.

Bob Sherman
Sr. Engineer, RTP Company
Message 5 of 10
nitinhadpe
in reply to: nitinhadpe

Hello Bob,

Thanks a lot again. That will certianly help.

Can we able to find the problematic Eigen value region?

Regards,
Nitin Hadpe
Sr. Engineer, Process CAE.
Neilsoft, Pune, India Edited by: nitinhadpe on Mar 31, 2010 4:50 AM
Regards,
Nitin Hadpe
Neilsoft Ltd, Pune, India
Message 6 of 10
BobSherman5561
in reply to: nitinhadpe

G'day Again Nitin,

Yes, if you have an analysis which has analyzed for the eigenvalues (2 lowest by default) either through the automatic analysis or the manually set Buckling Analysis, you can plot the eigenvalues which are simply shapes of the buckling mode. the key trick is to use the scaling tab on the result properties and set it to scale by frame (or each frame). Also you may need to set the magnitude down to something smaller than 1.0, say 0.25 - 0.5, it all depends a bit upon the size of your part and where the buckling is on your model. Then you should be able to show both solved eigenvalues and it will show the deflected shape with contours highlighting the maximum deflection areas.

Hope this helps,

Bob Sherman
Senior CAE Analyst, RTP Company
Message 7 of 10
nitinhadpe
in reply to: nitinhadpe

Thanks Bob,
That will be helpful for sure.

Regards,
Nitin Hadpe
Regards,
Nitin Hadpe
Neilsoft Ltd, Pune, India
Message 8 of 10
nitinhadpe
in reply to: nitinhadpe

Hello Bob,
Sorry to disturb you again but i have small question again regarding the same.
In warp, we get eigen values and some times we get negative values too.
Then what is the significane of negative Eigen value?

Regards,
Nitin H Edited by: nitinhadpe on Apr 9, 2010 12:18 PM
Regards,
Nitin Hadpe
Neilsoft Ltd, Pune, India
Message 9 of 10
BobSherman5561
in reply to: nitinhadpe

G'day Nitin,

The loads for a warpage analysis (it is a structural analysis) are the "free shrinkages" of each element based on the filling and packing prediction results. The structural analysis simply determines how these shrinkages will react with the stiffness of the part to determine how much shrinkage can occur and how the part will warp. So a negative eigenvalue represents what the part would do if the shrinkages were expansions, and that is of no physical use in this situation, so they can be ignored. The software is set-up to find the lowest 2 POSITIVE eigenvalues but the basic eigenvalue solution works in both the positive and negative direction.

Bob Sherman
Sr. CAE Analyst, RTP Company
Message 10 of 10
nitinhadpe
in reply to: nitinhadpe

Thanks Bob,
I got it completely.

Regards,
Nitin Hadpe
Regards,
Nitin Hadpe
Neilsoft Ltd, Pune, India

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