Augmentation of Residual Vector 1

[relaxrock]

Hi!
Does anyone now what is the residual vector?
I have a large model. After a modal solution I get two sets of eigenvalues. "Before augmentation of residual vector" and "After augmentation of residual vector". I have no idea what is this residual vector.

Regards
Ehsan Badri-Kouhi

 

[SaeidII]

Hope this will help.
There are some information on this in nastran 2001 release guide page 66 and 2004 release guide page 100.
good luck.

 

[BlasMolero]

Hello!,
In the NX NASTRAN I run, the term "RESIDUAL VECTORs" are an effective means for reducing the response errors by adding the missing static flexibility from the truncated modes, and it is available since NX NASTRAN 8.0 with the introduction of the RESVEC case control command, then enhanced further in NX Nastran 8.5 with additional options.

In fact, the modal method is a common approach for dynamic forced response solutions because of the computational efficiencies gained by the normal mode reduction. In practice, a small subset of the modes are computed and used for the computation while the effects of truncated higher frequency modes are ignored. The typical rule of thumb for modal sufficiency is to compute modes up to a frequency twice as high as the excitation frequency range. This is suitable for most responses, but some responses, in particular force and stress, can have errors because of the missing truncated modes. Since the missing modes have high frequencies, their omission leads to errors in the static response contributions.

Residual vectors are displacement shapes found from a static analysis that have been normalized. If a residual vector is not orthogonal to the normal mode shapes and the other residual vectors, it is discarded. The residual vectors that remain are used to "augment" the normal mode shapes in the eigenvector matrix. The augmented eigenvalue matrix is then used to transform the system matrices in physical space to a reduced representation in modal space. The reduced representation of the system in modal space is then used in the response calculation.

Best regards,
Blas.


~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

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[relaxrock]

Thanks but it is not what I mean.
anyway, thanks for ur attention.