Abstract
Rolling-element bearings are widely used in industrial rotating machines, and hence there is a strong need to accurately predict their influence on the response of such systems. However, this can be challenging due to an interaction between the dynamics of the rotor and the bearing nonlinearities, and it becomes difficult to provide a physical explanation for the nonlinear response. A novel approach, combining a Jeffcott rotor supported by a detailed bearing model with the generalised harmonic balance method, is presented, enabling an in-depth study of the complex rotor–stator interaction. This allows the quasi-periodic response of the rotor, due to variable compliance, to be captured, and the impact of clearance, ring and stator compliance, and centrifugal loading of the bearing on the response to be investigated. A strongly nonlinear response was observed due to the bearing, leading to large shifts in frequency as the excitation amplitude was increased, and the emergence of stable and unstable operating regions. The variable compliance effect generated sub-synchronous forcing, which led to sub-resonances when the ball pass frequency coincided with the frequency of one of the modes. Radial clearance in the bearing had by far the largest influence on the unbalance response, the self-excitation due to variable compliance, and the stability. Introducing outer ring compliance was found to slightly soften the system, and centrifugal loading on the bearing elements marginally increased the system’s region of instability, but neither of these effects had a significant impact on the response for the investigated bearing. When the bearing was mounted on a sufficiently compliant stator, the system was found to behave linearly.
Highlights
Rotating machines are used in a wide variety of applications, ranging from large-scale power-generation and aero-engines, to small-scale consumer goods such as computer hard drives
The clearance was set to the C2 level given in Table 1, corresponding to a radial clearance of 2.5 μm
The bearing model was coupled with a novel implementation of the generalised harmonic balance method, enabling a detailed study of the rotor-dynamic behaviour of a Jeffcott rotor
Summary
Rotating machines are used in a wide variety of applications, ranging from large-scale power-generation and aero-engines, to small-scale consumer goods such as computer hard drives. Vibration in such rotating systems can lead to performance reduction, malfunction, or even catastrophic failure. The rotor is assumed to move only in-plane, but is sufficient to investigate the unbalance response of the rotor, and can display resonance at certain critical speeds. This model has become a useful test case for
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