Model-Based Analysis of Friction-Induced Subsynchronous Whirl for a Rotor Contacting With Clearance Bearings Under Axial Load
12 Aug 2015-Journal of Engineering for Gas Turbines and Power-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 138, Iss: 7, pp 072507
TL;DR: In this paper, a set of constraint equations are derived that relate a circular whirl motion of arbitrary orbital speed to the frequency response functions of the rotor-housing structure, coupled with an evaluation of Coulomb friction associated with slip between the rotor and the supporting end-face of a thrust bearing.
Abstract: For rotors supported by active magnetic bearings (AMBs), clearance bearings are commonly used to provide backup support under loss of AMB functionality. Test data from real machines shows that rotor vibration during touchdown on backup bearings may involve steady forward whirling at a sub-synchronous frequency. This excitation is believed to be due to friction forces transmitted between the rotor and a bearing end-face under axial load. This paper proposes a new analytical approach to model and predict such friction-driven forward whirl behaviors. A set of constraint equations are derived that relate a circular whirl motion of arbitrary orbital speed to the frequency response functions of the rotor-housing structure. This model is coupled with an evaluation of Coulomb friction associated with slip between the rotor and the supporting end-face of a thrust bearing. The resulting equations can be used to compute a set of possible whirl motions via a root-finding procedure. A case study is undertaken for a 140 kW energy storage flywheel. Model-based predictions are compared with measured data from spin-down tests and show a good level of agreement. The study confirms the role of friction-related forces in driving forward-whirl response behaviors. It also highlights the key role of housing and machine support characteristics in response behavior. This influence is shown to be complex and not open to simple physical interpretation. Therefore, the proposed analytical method is seen as a useful tool to investigate this influence while avoiding the need for time consuming numerical simulations.Copyright © 2015 by ASME
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TL;DR: In this paper, the experimental behavior of a horizontal rigid rotor interacting laterally with two types of backup bearings during run up testing is analyzed by orbit analysis, spectrum analyzers, and force magnitudes collected by sensors installed.
7 citations
01 Jan 2017
TL;DR: In this paper, the authors explore the nonlinear rotor backup bearing dynamics both theoretically and experimentally using a fully instrumented test rig, where the position of shaft, its angular velocity and the contact forces between the shaft and the backup bearing are sampled at 25 kHz.
Abstract: Rotor drops in magnetic bearing and unbalance in rotors have been objective of study for many years. The combination of these two well-known phenomena led to an interesting chaotic response, when the rotor touches the inner race of the back-up bearing. The present work explores the nonlinear rotor backup bearing dynamics both theoretically and experimentally using a fully instrumented test rig, where the position of shaft, its angular velocity and the contact forces between the shaft and the backup bearing are sampled at 25 kHz. The test rig is built by a removable passive magnetic bearing, which allows for simulation of magnetic bearing failure (loss of carrying capacity and rotor fall). The rotor is studied numerically as well as experimentally. A theoretical approach is given beforehand and supplies the basis of the study. Finally the presented results are commented on the point of view of nonlinear dynamics applied to the practical use. The theoretical and numerical analyses are shown through orbit plots, phase plans, Poincaré maps, force response in time and double sided spectrum. The latter is important to characterize the condition at different levels of unbalance between forward and backward whirl. Our preliminary results indicate that for smaller amount of unbalance the rotor swings at the bottom of the bearing, the more the unbalance increases, other dynamical behavior occur and some can be extremely harmful, since the rotor can be lifted from the contact state and return, starting to impact innumerable times without reaching a steady state. & 2017 Elsevier Ltd. All rights reserved.
1 citations
Cites background from "Model-Based Analysis of Friction-In..."
...Subsynchronous whirl induced by friction was investigated by Cole and Hawkins in [44] and [45]....
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TL;DR: In this article , theoretical research based on a rotor-TDB model system is developed in order to predict the dynamic response of a vertical rotor drop failure, and the effectiveness of this model is validated by an AMB-tended touchdown bearing (TDB) rotor experiment.
References
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TL;DR: In this article, the rotor and stator are regarded as linear multi-degree-of-freedom systems including damping, and dry friction at the clearance space is taken into account.
Abstract: Where a rotor runs within a clearance space, the clearance being comparable with rotor mass unbalance, the synchronous whirling behaviour of the rotor may be considerably affected by intermittent interaction with the stator at the clearance position. Discontinuity and jump phenomena may occur: in general, behaviour will be different with increasing speed from that with decreasing speed, and in either case zones may exist in which rotor-stator interaction is possible but not certain. In the analysis here presented, rotor and stator are regarded as linear multi-degree-of-freedom systems including damping; dry friction at the clearance space is taken into account. Discussion is limited to cases with radial symmetry, and interaction is assumed limited to the position of the clearance space. Polar receptances are used to establish equilibrium conditions with interaction, and speed zones are defined within which interaction may occur. Some hypothetical cases are fully explored, demonstrating that rotor-stator i...
162 citations
TL;DR: In this paper, the authors present numerical analysis for a rotor drop on catcher bearings and following thermal growths due to their mechanical rub using detailed CB and damper models. Butler et al. used a finite element squeeze film damper to provide the pressure profile of an annular oil film and the resulting viscous damping force.
49 citations
01 Oct 2003
TL;DR: In this article, the dynamics of a multimode rotor-bearing system are analyzed when the rotor contacts with a stator having annular clearance, using a harmonic decomposition with generalized fundamental frequency, periodic solutions are obtained for rotor motions that involve asynchronous periodic contact.
Abstract: The dynamics of a multimode rotor-bearing system are analysed when the rotor contacts with a stator having annular clearance. By transforming to a rotating frame, all possible steady state rotor vibration modes that involve periodic contact with the surround may be predicted. Using a harmonic decomposition with generalized fundamental frequency, periodic solutions are obtained for rotor motions that involve asynchronous periodic contact. The analytical solutions are compared with previously published experimental results, which are predicted with considerable accuracy thus confirming the efficacy of the approach. Solutions are obtained for different test cases, which show how the amplitude and stability of the periodic contact modes are dependent on system parameters and operating conditions. In particular, for increased unbalance levels, the amplitude of the contact mode vibration is increased and the response of the rotor progresses from a bouncing forward whirl to a backward whirl-type motion. ...
40 citations
TL;DR: In this paper, the synchronous interaction dynamics methodology is applied to a flexible rotor system and comparisons are made between the behavior predicted by this analysis method and the observed simulation response characteristics. And experimental studies are also performed to validate the simulation results and provide insight into the expected behavior of such a system.
Abstract: This study investigates the application of synchronous interaction dynamics methodology to the design of auxiliary bearing systems. The technique is applied to a flexible rotor system and comparisons are made between the behavior predicted by this analysis method and the observed simulation response characteristics. Of particular interest is the influence of coupled shaft/bearing vibration modes on rotordynamical behavior. Experimental studies are also perFormed to validate the simulation results and provide insight into the expected behavior of such a system.
36 citations
TL;DR: In this article, a high-performance, high-speed permanent magnet, direct-drive generator and low-loss magnetic bearings are described for a cryogenic gas expander system.
Abstract: A cryogenic gas expander system that incorporates a high-performance, high-speed permanent magnet, direct-drive generator and low loss magnetic bearings is described. Flow loop testing to 30,000 rpm was completed at the system manufacturer's facility in January 2005, and field installation is scheduled for October 2005. As part of the system testing, the rotor was dropped onto the backup bearings multiple times at an intermediate speed and at 30,000 rpm. Orbit and time-history data from a full speed drop and spin down are presented and discussed in detail. A transient, nonlinear rotordynamic analysis simulation model was developed for the machine to provide insight into the dynamic behavior. The model includes the dead band clearance, the flexible backup bearing support, and hard stop. Model predictions are discussed relative to the test data.
31 citations