5 Replies Latest reply on Feb 4, 2013 2:35 PM by Nathan Obermiller

    Mass Participation Greater than Unity

    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.