Assessment of numerical model to determination of parameters to stability experimental tests

Abstract

Rotating machines have to meet rigorous requirements in order to prevent instability during its operation. In the context of stability analysis, experimental tests such as stepped sine are widely used to determine the modal parameters of rotating systems: forward and backward natural frequencies and damping factors. Nevertheless, classical modal analysis techniques require prior knowledge of the system behavior, so that rotational speed and external excitation frequencies can be defined for the experimental tests. This work aims the assessment of model based numerical calculations to reduce or even stave off the preliminary tests. Validation starts with the evaluation of lubricated bearings model by shaft center locus. Afterwards, mass unbalance response is evaluated, and then, the stability analysis is conducted based on the logarithmic decrement. Finally, the numerical evaluation is compared to an experimental procedure regarding the precision of predicted critical frequencies for the tests and the evaluation of stability threshold.