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April 30, 2021 at 11:39 am
ysngrg
SubscriberHello 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 .
April 30, 2021 at 11:47 amErik Kostson
Ansys EmployeeWe 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
April 30, 2021 at 11:53 amysngrg
SubscriberWhen 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?
April 30, 2021 at 11:56 amErik Kostson
Ansys EmployeeThere 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
April 30, 2021 at 11:57 amysngrg
SubscriberYes, clear, thank you.
April 30, 2021 at 11:59 amErik Kostson
Ansys EmployeeNo 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:
June 20, 2023 at 11:13 amBALA
Subscriberwhat if even after exttractin more number of modes the ratio of effective mass is still less
Viewing 6 reply threads- The topic ‘How many modes should I extract?’ is closed to new replies.
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