I would very much appreciate your help with the following:
I'm trying to do a modal analysis of a bracket with a 22.7kg added mass as part of a dynamics course I'm attending. Unfortunately, the frequencies I'm getting from Robot are completely different from the ones in the example.
The model seems to be geometrically correct, the mass is correct, I've tried different options (consistent, lumped masses, more refined mesh, etc) and the results seem to be roughly the same everytime.
The frequencies I was expecting are:
Mode 1 - 108.41 Hz (Robot = 100.17 Hz)
Mode 2 - 130.08 Hz (Robot = 1003.86 Hz)
Mode 3 - 429.16 Hz (Robot = 1159.38 Hz)
Mode 4 - 1607.53 Hz (Robot = 1421.37 Hz)
Mode 5 - 1817.43 Hz (Robot = 2512.01 Hz)
Mode 6 - 3519.18 Hz (Robot = 2674.27 Hz)
Mode 7 - 3573.52 Hz (Robot = 3028.08 Hz)
Mode 8 - 4267.00 Hz (Robot = 3246.49 Hz)
Mode 9 - 4768.45 Hz (Robot = 3513.84 Hz)
Mode 10 - 5133.30 Hz (Robot = 3686.09 Hz)
I'm fairly inexperient with this subject and would really appreciate some help, particularly because this becoming a bit frustrating since it is the second example I try (both of them very straight forward) and don't get any correlation between the results...
What are reference values?
Can you send us this Nafems original example or at least its name \ numer?
- selfweight is doubled for Modal analysis
- results with 1 sw + mass as it is - first mode - 100.21 Hz
- results with no sw + mass as it is - 100.25 Hz
- results with no sw - mass acting in UX UY UZ - 99,81 Hz