Normalized eigenvectors

[aeromecha]

Hi,

Does anyone know how the eigenvectors are normalized in cyclic symmetry analysis of ANSYS 7.0?
By the way, I found the following information in ANSYS website.

In modal cyclic symmetry, this becomes even more complicated because of the presence of the duplicate sector. Here the mass normalization is [ [phi]a~ [M] [phi]a + [phi]b~ [M] [phi]b =1]. When two sectors are used, the scaling factor of sqrt(1/2) is still valid, but it should be applied on the magnitude: i.e, sqrt (real**2+imaginary**2).

......When I conduct this calculation, I can't get the unit matrix. Please let me know if you're familier with this.

Tommy

 

[Drej]

In ANSYS, the eigenvector normalisation is controlled by the MODOPT command:

MODOPT, Method, NMODE, FREQB, FREQE, PRMODE, Nrmkey

The Nrmkey controls this normalisation by using either

OFF — Normalize the mode shapes to the mass matrix (default).

ON — Normalize the mode shapes to unity instead of to the mass matrix. If a subsequent spectrum or mode superposition analysis is planned, the mode shapes should be normalized to the mass matrix (that is, Nrmkey = OFF).

So by default, these are normalised to the mass matrix. To get the these normalised to unity, use Normkey = on, or go to:

Main Menu>Preprocessor>Loads>Analysis Type>Analysis Options
Main Menu>Solution>Analysis Type>Analysis Options




------------
See faq569-1083 for details on how to make best use of Eng-Tips.com

 

[aeromecha]

Drej,

Thank you for your response.
Yes, I turned off the MODOPT option.

Then, I get mode shapes in real and imaginary form. (for basic and duplicate sector).
My question is how I can compute the unit matrix using those mode shapes and mass matrix of the basic sector.

Tommy