Effect of Assembled Bearing Inner Ring Geometry on Subcritical Rotor Vibration

Research output: ThesisDoctoral ThesisCollection of Articles


In many industrial fields, large flexible rotors are commonly operated within the subcritical speed range, where the bearings are a considerable source of vibration excitation. The dynamic properties and the rotational accuracy of a bearing are greatly affected by the roundness profile of the bearing inner ring installed on the rotor shaft. The final roundness profile of the inner ring is the sum of the roundness profile of the rotor shaft roundness and the thickness variations of the relatively flexible inner ring and the possible conical adapter sleeve. The excitation based on the roundness errors of a bearing inner ring is observed at a frequency, which is the rotor rotating frequency multiplied by the number of undulations in the roundness profile of the ring. Therefore, subcritical resonance is observable at rotor frequencies, which are integer fractions of the natural frequency of the system, i.e., when the bearing excitation frequency equals the natural frequency of the rotor system. The present study investigated the effect of the roundness profile of the installed bearing inner ring on the subcritical vibrations of a flexible rotor. The roundness profile of the assembled bearing inner ring was measured and modified to five different geometries to investigate different excitation cases. Finally, the roundness error of the inner ring was minimized. The rotor subcritical response was measured with each bearing inner ring geometry. The analysis was focused on the 2nd, 3rd and 4th harmonic subcritical resonances, occurring at 1/2, 1/3 and 1/4 of the natural frequency. In addition, the uncertainty of the bearing roundness profile measurement based on the four-point method was analysed. The four-point roundness measurement method is able to separate the roundness profile from the error motion of the rotating axis during the measurement. Conventional roundness measurement machines could not be used to measure the roundness of an installed bearing inner ring due to the large size of the workpiece. Finally, a device and a method for measuring the thickness variation of large roller element bearing rings was presented to investigate the root causes for the out of roundness of the installed bearing inner ring. The results clearly suggest that the roundness components of the installed bearing inner ring significantly affect the rotor subcritical vibration. The increased amplitudes of certain waviness components of the bearing inner ring roundness profile increased the corresponding subcritical vibration amplitude. Minimizing the roundness error decreased the vibration substantially. In addition, the uncertainty analysis of the roundness measurement of the installed bearing inner ring confirmed that the method is valid and the uncertainty is acceptable for the application. Moreover, the device and method for thickness variation measurement of the bearing elements was found to reach a comparable level of measurement accuracy with conventional roundness measurement machines, but without similar dimensional restrictions and with a more direct measurement chain.
Translated title of the contributionAsennetun laakerin sisäkehän geometrian vaikutus roottorin alikriittiseen värähtelyyn
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Kuosmanen, Petri, Supervising Professor
Print ISBNs978-952-60-8195-3
Electronic ISBNs978-952-60-8196-0
Publication statusPublished - 2018
MoE publication typeG5 Doctoral dissertation (article)


  • bearing excitation
  • harmonic components
  • low-order bearing waviness
  • bearing thickness variation
  • four-point method
  • measurement uncertainty evaluation


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