Learning Forum

[ysngrg]

Hello to All;

I want to solve random vibration analysis. My vibration profile up to 500 Hz. When I extract my modal results up to 500 Hz is it enough? or Should I check my modal results acording to sum of mass participation factor and I should extract modes up to higher mass participation factor if not I do not have vibration profile that frequencies.

Thanks .

[Erik Kostson]

We should extract as many modes so our Ratio of Effective Mass to Total Mass is larger than about 0.9 for the direction(s) of interest. Like shown below.
(this table can be seen under solution information and instead of solution output choose participation factors summary - see image below).

ALl the best

Erik

[ysngrg]

When I extract modes above 0.9, such as I will have many modes above the 500 Hz, but my profile up to 500 Hz, I do not have any vibration load after 500 Hz.
Should I extract these modes?

[Erik Kostson]

There is no frequency limit - the only thing we need to care about is to have a Ratio of Effective Mass to Total Mass larger than about 0.9 (this is a common number and often used in some structural codes dealing with seismic design of structures), so we need to include enough modes that we achieve this ratio.

Hope that is clear now.

Thank you

Erik

[ysngrg]

Yes, clear, thank you.

[Erik Kostson]

No worries - glad to be of help.

All the best
And for anyone interested in this, there is a nice course that explains the above in detail - hope you find it useful:

[balaji.bp]

what if even after exttractin more number of modes the ratio of effective mass is still less