Number of missing eigenvalues found

[pevelor]

Hi

During modal analysis I get message saying the following:

Number of missing eigenvalues found = 2.

What does this message indicate?

Kind regards

Peder

[Artur.Kosakowski · Accepted solution]

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Eigenvalues/td-p/3201388

and

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Tips-for-using-Search-in-the-Autodesk-Forums... :

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[pevelor]

I am sorry for asking before thoroughly seaching. Anyways, thanks for your assistance.

[Artur.Kosakowski]

No problem. Feel free to ask any question you want. I know it is much easier to search when you already know the answer

[Μηχανικος]

I have the same issue

Number of missing eigen values found = 1

The issue did not appear until i decided to change the thickness of the slab at a section of the ground storey where the car park is located. Therefore i have different thickness of slab on the same floor.

can anyone understnd why by changing the thickness of the slab this type of issue appeared?

[Artur.Kosakowski]

Most likely such changed influenced the values of eigenfrequencies in such way that the initial run of the solver skipped one that was very closed to another. This may happen due to the nature of the solution itself and this is why the Sturm check verification is included in the the modal analysis parameters. 

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[Μηχανικος]

Thank you for the reply....do you always use the sturm check in modal analysis?

[Artur.Kosakowski]

When I need to determine the values of eigenfrequences e.g. when I need to avoid the resonanse I always do (applies to buckling analysis too). On the other hand for seismic analysis when you need 90% of participating masses I usually don't as missing eigenvalues are not likely to be importantf or this kind of analysis and serach for them makes the calculation time to be longer. 

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[Μηχανικος]

What about seismic analysis with design response spectrum, you still don't use the storm check?

[Artur.Kosakowski]

"On the other hand for seismic analysis when you need 90% of participating masses I usually don't as missing eigenvalues are not likely to be important for this kind of analysis and search for them makes the calculation time to be longer. "

In other words it is unlikely that the missing eignenvalue will be this which produces significant participating mass percentage when you reached 90% for others 

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[marcos.wanke]

Dear Artur,

In buckilng analysis these 'missing eigenvalues' are refered to the firsts (lower values) or last eigenvalues (higher values)^?

[Artur.Kosakowski]

Hi @marcos.wanke

You can't tell exactly. Some between the first and the last.

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[Anonymous]

Dear Artur,

First, really thank you for your help in pervious chats, I noted some notes for eigenvalues missing issue.
When I don't delete the mesh that generated from last calculation before run a new calculation, this waring (eigenvalues missing) appears. Any relation between it?

Also, How can I create cladding with irregular shapes (contour).

Best regards,
Mohammed