[MBDyn-users] question about eigenanalysis

lengjun lengjun1007 at 163.com
Tue Nov 14 07:56:24 CET 2017


Dear all,
I have a problem about the eigenanalysis of a cantilever. I set a reference called arm:
reference: arm,
 reference, global, 0., 0., 1.,
 reference, global, eye,
 reference, global, null,
 reference, global, 0., 0., omega;
and all nodes and elements are in the 'arm' reference.
the result of frequency are incorrect:
##############################################################################
# Key for lines starting with "Step":
# Step Time TStep NIter ResErr SolErr SolConv Out
Step 0 0 0 0 0 0 0 1
Step 1 0.001 0.001 0 0 0 0 1
# Derivatives solution step at time 0 performed in 0 iterations with 0 error
Info: 0, success BALANC="B" ILO=7 IHI=226 ABNRM=4.62438e+16 BBNRM=4.62438e+16
Mode n.       Real           Imag             Damp %     Freq Hz
# Key for lines starting with "Step":
# Step Time TStep NIter ResErr SolErr SolConv Out
Step 0 0 0 0 0 0 0 1
Step 1 0.001 0.001 0 0 0 0 1
##############################################################################
However ,when I changed the reference 'arm' into:
reference: arm,
 reference, global, 0., 0., 0.,
 reference, global, eye,
 reference, global, null,
 reference, global, 0., 0., omega;


it goes well. the results are:
# Derivatives solution step at time 0 performed in 0 iterations with 0 error
Info: 0, success BALANC="B" ILO=7 IHI=226 ABNRM=1.24038e+10 BBNRM=1.24038e+10
Mode n.       Real           Imag             Damp %     Freq Hz
       7: -3.07437e-08 +       38.281 j     8.03108e-08          6.0926
       9:  1.11572e-09 +       38.281 j    -2.91457e-09          6.0926
      11:   1.4287e-08 +      234.684 j    -6.08777e-09         37.3511
      13:  1.41642e-08 +      234.684 j    -6.03545e-09         37.3511
      15:  7.43393e-08 +      635.257 j    -1.17022e-08         101.104
      17:  1.41226e-07 +      635.257 j    -2.22314e-08         101.104
      19:  1.84635e-09 +      697.431 j    -2.64735e-10             111
      21:  1.25765e-07 +       1189.2 j    -1.05756e-08         189.267
      23: -1.27215e-07 +       1189.2 j     1.06975e-08         189.267
      25:  1.05445e-07 +      1863.02 j     -5.6599e-09         296.508
      27: -1.74265e-09 +      1863.02 j     9.35393e-11         296.508
      29:  6.88544e-08 +      2622.68 j    -2.62534e-09         417.413
      31: -4.36833e-08 +      2089.71 j      2.0904e-09         332.588
      33: -7.66471e-08 +      3438.49 j     2.22909e-09         547.253
      35:  9.22549e-08 +      2622.68 j    -3.51757e-09         417.413
      37: -1.77564e-08 +      4283.13 j     4.14566e-10         681.682
      39: -6.07606e-08 +      3438.49 j     1.76707e-09         547.253
      41:  7.44935e-09 +      3474.15 j    -2.14422e-10         552.928
      43:  -6.6307e-08 +      4283.13 j      1.5481e-09         681.682
      45: -3.87825e-08 +      4845.22 j     8.00427e-10         771.141
      47:  1.29202e-07 +      5124.28 j    -2.52136e-09         815.554
      49:  1.03002e-06 +      5881.29 j    -1.75136e-08         936.036
      51:  4.21351e-07 +      5124.28 j    -8.22264e-09         815.554
      53:  2.84468e-07 +      5881.29 j    -4.83682e-09         936.036
      55:  2.56009e-07 +      6196.96 j    -4.13121e-09         986.277

I am wodering if the results are related to the position of the reference. The attachments are the input files.
Best wishes.
 Iris
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