How to evaluate a failure of a rotary equipment (molecular turbo pump) in which they can generate a large torque over a period of time and their effect on our piping system must be evaluated?
Please see suggested response on a specific model that cannot be shared, but the approach is still valid.
1) The cutoff frequency must be greater than the inverse of the period of the fastest phenomenon.
Example, if the torque pulse lasts 1.5 ms, the cutoff frequency must be equal to or greater than 667 Hz (calculated value from a different application).
2) For simplicity, the modal analysis technique only considers displacements, linear accelerations and forces as boundary conditions. To include a torque, as is the case, must represent it with acouple of forces and arms.
3) Model a weightless rigid tubes or weightless rigid beams can be used as arms from the center of the pipe perpendicular some distance. Then specify a Time history force at this new location that would cause a torque over a period of time.
Note, one advantage of the weightless rigid beam is that they do not require additional segments and are not listed in the results of tensions.
Model Pump / Compressor (Oscillating) Vibration