When calculating eigenvectors with RF-/DYNAM Pro, I receive effective modal mass factors, which are all approximately 0. What can be the reason for this?

Answer

The cause of small effective modal mass factors can be very diverse. Often, this can be observed for larger structures. The reason for this problem consists in most cases in the fact that only local eigenvectors occur. The following describes how you can handle this point:


  • If they really refer to local eigenvectors, or not, should be analyzed in the results graphic. If single members or surfaces have a very low angular frequency, they occur first.
  • If you want to include these local eigenvectors in the calculation, you should increase the number of eigenvectors to be calculated.
  • If local eigenvectors occur on surfaces, the masses of the affected surfaces can be neglected. This feature is described in this article .
  • In case of local eigenmodes on members, it is recommended to deactivate the FE mesh splitting on members.
If all of these notes have been observed, only the global eigenmodes of the structure should be activated, which also activate a high mass.

Keywords

Effective modal mass Modal mass factor Eigenvector Dynamic Mass

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