Free modal analysis with MPC results 6 no-zero rigid body modes

Zhou XU
Zhou XU Altair Community Member
edited July 2022 in Community Q&A

a free-free modal analysis in Simlab Solution (Optistruct solver). the model has seveal parts connecting with MPCs as in picture. the MPC equations are built in Simlab by "Connect Faces".

as following tabe, the 6 rigid modes are not zero, but about 20 Hz max. i know the problem should be MPC coefficient. my questions are,

1. how to fix the MPC coefficient in simlab connect faces, make independent nodes coefficent equal to 1? (to make MPC as RBE2 or RBE3)

2. if the 6 rigid body modes are not zero Hz, is it OK ?

Subcase Mode Frequency Eigenvalue Stiffness Mass
1 1 5.149629E-01 1.046916E+01 1.046916E+01 1.000000E+00
1 2 5.178920E-01 1.058859E+01 1.058859E+01 1.000000E+00
1 3 6.468625E-01 1.651900E+01 1.651900E+01 1.000000E+00
1 4 1.987561E+01 1.559555E+04 1.559555E+04 1.000000E+00
1 5 2.035556E+01 1.635783E+04 1.635783E+04 1.000000E+00
1 6 2.045624E+01 1.652005E+04 1.652005E+04 1.000000E+00
1 7 2.464441E+03 2.397710E+08 2.397710E+08 1.000000E+00
1 8 2.566454E+03 2.600319E+08 2.600319E+08 1.000000E+00
1 9 3.230375E+03 4.119701E+08 4.119701E+08 1.000000E+00
1 10 3.235322E+03 4.132328E+08 4.132328E+08 1.000000E+00

 

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