Hi
Is anyone here knows if the rigid pseudo modes are included in spectral analysis made by SimMech?
Thanks
Hi @drutel
Let me make sure that I (and the other readers) understand your question. Is this an accurate description of your process?
The answer is yes: technically, the rigid body modes are included in the vibration analysis.
However, the rigid body modes should not affect the vibration results because of the following:
Hi
We were talking about the ability of the spectral analysis (and not the modal one) which sometimes includes the pseudo rigid modes into its solution prediction.
It is very used in the nuclear industry...
Alain,
To put John's answer in different, and less, words:
A model analysis can produce near zero pseudo modes if the model is not statically stable.
Of course, it is only the modal analysis that can generate pseudo, along with the valid, modes. The other restart analyses such as response spectrum will use all the frequencies (pseudo and valid non-zero) in calculations.
The restart analyses (e.g. spectral) do not know, or care, that the model is not statically stable. Results of such analyses should not be effected by the pseudo modes.
Hi
The model is statically stable
but since the first frequency is very high and the spectra not goes til that frequency.
So a method allows to use rigid pseudo modes to send excitations to the structure to be sure to recover all the response
please see this link for example : http://www.freelem.com/theorie/spectrale.htm
Regards
Hi Alain,
Thanks for the clarification. The question is different than I thought.
The answer is no: Simulation Mechanical does not have that type of capability.
The key paragraph from the Freelem website is as follows:
The page goes on to describe how to calculate the response due to frequencies above the range of the spectrum (and frequencies not included in the modal analysis, if I understand it correctly.)
It would be interesting to know how much of an affect those pseudo-modes have on the result, versus the frequency. For example, a natural frequency that is X times higher than the response spectrum adds a% to the stress, a frequency Y times higher than the response spectrum adds b% to the stress, and so on. As the frequency gets higher (X to Y to Z to ...), the contribution gets lower (a% to b% to ....).