the effective mass of the frequency analysis is more than the total mass of the model for some cases 2

[kumara123]

Hi,
I ran a frequency analysis in Abaqus to find the first natural frequency and frequency related 95% model mass. The obtained participation factors are very much low and also effective mass (e.g - 6.74E9) for the rotation components are larger than the total mass of the model (4.27E7). Can anyone explain this to me, please? the .dat file is attached here.
Thank you.

 

[JGard1985]

The last time I had problems like this, I had elements that we're not connected to adjoining elements. Check your deflected shapes and make sure you have the correct response with boundary conditions. Yopu dont want single unconnected elements bouncing around



Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[GregLocock]

Physically it is possible to have a larger modal mass than model mass, depending on how you normalise for modal mass. There are at least 3 ways, which give very different answers.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[kumara123]

Hi Jeff and Greg, Thanks for your reply.

I could not find any unbonded elements in my model. But still, I have the problem with obtaining frequency related to 95% model mass.
I extracted 30 modes and participation factors are added together, the values are very low (e.g. 1.5, 2.3 and 2.0 for three components). Should I want to extract more modes (until I get the summation of 95) to find model mass related with 95% model mass? please find the attachment of the participation factors.
If you have any suggestions, please let me know.