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Mass Participation Greater than Unity

Question asked by Nathan Obermiller on Jan 31, 2013
Latest reply on Feb 4, 2013 by Nathan Obermiller

All,

I am somewhat of a newbie with Solidworks Simulation.  I am running a frequency study on a linear segment of a structural tube member with a fixed top support and 6 simple "immovable" supports on 6 joints of equal spacing.  I am trying to validate a study using William F. Stokey, Vibration of Systems Having Distributed Mass and Elasticity, Chapter 7, Table 7.5 Case 3.  I have tried modeling the example (rigid with N number of simple supports) with shells and solid bodies with no luck.  Using the beam method is the only way I've come across that give reasonable results and accurate results compared to the textbook case.  However, I am getting mass participation sums greater than 1 with only a few modes.

 

Mode No. Freq (Hertz) X direction Y direction Z direction

1 88.865       5.8614e-011  3.9844e-034  0.016617   

2 93.58        0.016617     1.0651e-033  5.8614e-011

3 93.58        0.026818     7.5529e-033  2.8911e-010

4 107.04       2.8911e-010  3.1116e-034  0.026818   

5 107.04       8.9219e-007  1.4724e-036  0.065241   

6 129.83       0.065241     1.1957e-032  8.9219e-007

7 129.83       0.55731      2.2588e-033  5.6867e-008

8 157.39       5.6867e-008  3.9083e-035  0.55731    

9 157.39       2.8661e-029  0            3.8163e-030

10 185.07       9.6251e-005  5.724e-034   0.0024821  

11 185.07       0.0024821    9.2071e-033  9.6251e-005

12 204.87       0.55731      2.2588e-033  5.6867e-008

13 204.87       5.6867e-008  3.9083e-035  0.55731    

14 266.6        2.8661e-029  0            3.8163e-030

15 367.66       9.6251e-005  5.724e-034   0.0024821  

16 367.66       0            0            0          

    Sum X  = 1.226        Sum Y  = 3.6234e-032  Sum Z  = 1.2284    

 

 

My questions is, what does a mass participation greater than 1 represent.  I know some of my modes that have >1% mass participation are probably incorrect by just looking at the mode shape.  Any thoughts?

 

Thank you.

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