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Bernhard Schweizer - One of the best experts on this subject based on the ideXlab platform.
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Stability and bifurcation phenomena of Laval/Jeffcott rotors in semi-floating ring bearings
Nonlinear Dynamics, 2015Co-Authors: Aydin Boyaci, Bernhard SchweizerAbstract:Within this contribution, a linear-elastic Laval/Jeffcott rotor is considered, which is symmetrically supported in two identical semi-floating ring bearings. Run-up simulations and bifurcation analyses are carried out to investigate the stability and bifurcation phenomena of the rotor-bearing system. In particular, the methods of numerical continuation are applied to identify the nonlinear phenomena (jump phenomena, coexistence of solutions, etc.) and the corresponding bifurcations. The occurrence of subsynchronous oscillations is examined, which is caused by an Oil Whirl/whip instability due to the inner Oil films. In this case, the main damping is provided by the outer Oil films so that the oscillation amplitudes usually remain moderate. Besides these well-known subsynchronous oscillations with moderate amplitudes (Oil Whirl/whip instability due to the inner Oil films), it is shown that self-excited oscillations with very high amplitudes also exist. This effect resembles Total Instability known from rotors in full-floating ring bearings. A detailed bifurcation analysis proves the coexistence of a so-called critical limit cycle with high amplitudes in the case of the perfectly balanced rotor which represents Total Instability. Finally, a variation of rotor and bearing parameters shows the influence on both the subsynchronous oscillations of tolerable amplitudes and the critical limit cycle oscillations.
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Oil Whirl, Oil whip and Whirl/whip synchronization occurring in rotor systems with full-floating ring bearings
Nonlinear Dynamics, 2009Co-Authors: Bernhard SchweizerAbstract:High-speed rotors are often supported in floating ring bearings because of their good damping behavior. In contrast to conventional hydrodynamic bearings with a single Oil film, full-floating ring bearings consist of two Oil films: An inner and an outer Oil film. As single Oil-film bearings, full-floating ring bearings also show the typical fluid-film-induced instabilities (self-excited vibrations). Both inner and outer Oil films can become unstable and exhibit Oil Whirl/whip instabilities. The paper at hand considers a Laval (Jeffcott) rotor, which is symmetrically supported in full-floating ring bearings, and investigates the occurring Oil Whirl / whip effects by means of run-up simulations. It is shown that the inner Oil film, which usually becomes unstable first, gives rise to a limit-cycle oscillation with an exactly circular rotor orbit, if gravity and imbalance are neglected. Interesting is the instability generated by the outer Oil film. The calculations demonstrate that instability in the outer Oil film does not lead to a simple circular limit-cycle orbit. Whirl/whip -induced limit-cycle oscillations generated by the outer Oil film are more complex and entail a coupled circumferential and radial motion, although the mechanical problem is radially symmetric, if gravity and imbalance are neglected. Thus, Whirl/whip instability in the outer fluid film may be interpreted as symmetry breaking. Finally, a further kind of bifurcation/instability occurring in rotors supported in full-floating ring bearings—called Total Instability in this paper—is analyzed. It is shown that Total Instability is caused by synchronization of two limit cycles, namely synchronization of the inner and outer Oil Whirl/whip . Total Instability is of practical interest and observed in real technical rotor systems, and frequently leads to complete rotor damage.
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Oil Whirl, Oil whip and Whirl/whip synchronization occurring in rotor systems with full-floating ring bearings
Nonlinear Dynamics, 2009Co-Authors: Bernhard SchweizerAbstract:High-speed rotors are often supported in floating ring bearings because of their good damping behavior. In contrast to conventional hydrodynamic bearings with a single Oil film, full-floating ring bearings consist of two Oil films: An inner and an outer Oil film. As single Oil-film bearings, full-floating ring bearings also show the typical fluid-film-induced instabilities (self-excited vibrations). Both inner and outer Oil films can become unstable and exhibit Oil Whirl/whip instabilities.
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Oil Whirl Oil whip and Whirl whip synchronization occurring in rotor systems with full floating ring bearings
Nonlinear Dynamics, 2009Co-Authors: Bernhard SchweizerAbstract:High-speed rotors are often supported in floating ring bearings because of their good damping behavior. In contrast to conventional hydrodynamic bearings with a single Oil film, full-floating ring bearings consist of two Oil films: An inner and an outer Oil film. As single Oil-film bearings, full-floating ring bearings also show the typical fluid-film-induced instabilities (self-excited vibrations). Both inner and outer Oil films can become unstable and exhibit Oil Whirl/whip instabilities.
N. Yazdandoost - One of the best experts on this subject based on the ideXlab platform.
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Oil Whirl Fault Detection in Sleeve Bearing of Induction Motor by Using Instantaneous Power Harmonics
2016Co-Authors: M. Ojaghi, N. Yazdandoost, S. GholmohammadzadehAbstract:Harmful impacts of Oil Whirl fault in sleeve bearing can be avoided by early detection of the fault. In this paper, after describing the Oil Whirl fault, an analytic approach is applied to determine frequency of the harmonics produced by the fault in instantaneous power waveform of induction motor. Then, using appropriate air gap function, winding function approach is used for simulating squirrel cage induction motor with bearing Oil Whirl fault. The instantaneous power spectrum, plotted using simulation results, approves creation of the proposed harmonics. These harmonics are also evident in instantaneous power of an induction motor that operates on Oil pipe line, where vibration analysis shows presence of Oil Whirl fault in its bearing. Finally, the most appropriate harmonic as the Oil Whirl fault index is selected using simulation by considering their relative amplitudes as well as their sensitivity to the fault type, fault degree, motor load level and three-phase unbalance of the stator voltages.
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Oil-Whirl Fault Modeling, Simulation, and Detection in Sleeve Bearings of Squirrel Cage Induction Motors
IEEE Transactions on Energy Conversion, 2015Co-Authors: M. Ojaghi, N. YazdandoostAbstract:Bearings are divided into two main categories: rolling bearings and sleeve bearings. The sleeve bearings are normally used in electrical machines above 200-hp rating. In this paper, dynamic modeling and simulation of a squirrel cage induction motor with sleeve bearings under Oil-Whirl fault is performed. The required air gap function under the fault is defined using earlier experimental results. Then, a winding function approach is used for modeling and simulation of the motor with faulty sleeve bearings. Accuracy of the simulation is approved by comparison to the corresponding experimental results. The stator line current harmonics produced by the bearing Oil-Whirl fault are identified, and the best harmonics as the fault index are chosen considering sensitivity of the harmonics to the fault severity, as well as the load level change and supply voltage unbalance. Selected index is used to determine the severity of Oil-Whirl fault in sleeve bearing of an induction motor working in a real production line.
M. Ojaghi - One of the best experts on this subject based on the ideXlab platform.
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modeling induction motors under mixed radial axial asymmetry of the air gap produced by Oil Whirl fault in a sleeve bearing
IEEE Transactions on Magnetics, 2018Co-Authors: M. Ojaghi, Reza AkhondiAbstract:High-power rating three-phase squirrel cage induction motors (SCIMs) may be equipped with sleeve bearings (SBs). Oil-Whirl fault (OWF) is an important fault mode of the SBs, which can lead to their serious damage. On-line condition monitoring is recommended to detect possible incipient OWFs in the SBs before total failure of them and catastrophic stop of the machine. The OWF usually happens only in one of the motor SBs and introduces time-variant mixed radial–axial asymmetry to the air gap distribution. To study the SCIM performance under the OWF in one of its SBs, this paper proposes an analytical modeling and simulation approach. Multiple coupled circuit modeling along with the 2-D modified winding function theory is used for this purpose. The modeling and simulation results show novel harmonic components in the stator line currents, as well as the self-inductances of the stator windings due to the fault. The latter harmonics can be used as indices for diagnosing the bearing OWFs as well. Regarding the sensitivity to the fault severity and robustness against the load level change and the mains voltage unbalance degree change, simulation-based studies are used to determine the most appropriate inductance harmonic as the OWF index.
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Modeling Induction Motors Under Mixed Radial–Axial Asymmetry of the Air Gap Produced by Oil-Whirl Fault in a Sleeve Bearing
IEEE Transactions on Magnetics, 2018Co-Authors: M. Ojaghi, Reza AkhondiAbstract:High-power rating three-phase squirrel cage induction motors (SCIMs) may be equipped with sleeve bearings (SBs). Oil-Whirl fault (OWF) is an important fault mode of the SBs, which can lead to their serious damage. On-line condition monitoring is recommended to detect possible incipient OWFs in the SBs before total failure of them and catastrophic stop of the machine. The OWF usually happens only in one of the motor SBs and introduces time-variant mixed radial-axial asymmetry to the air gap distribution. To study the SCIM performance under the OWF in one of its SBs, this paper proposes an analytical modeling and simulation approach. Multiple coupled circuit modeling along with the 2-D modified winding function theory is used for this purpose. The modeling and simulation results show novel harmonic components in the stator line currents, as well as the self-inductances of the stator windings due to the fault. The latter harmonics can be used as indices for diagnosing the bearing OWFs as well. Regarding the sensitivity to the fault severity and robustness against the load level change and the mains voltage unbalance degree change, simulation-based studies are used to determine the most appropriate inductance harmonic as the OWF index.
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Oil Whirl Fault Detection in Sleeve Bearing of Induction Motor by Using Instantaneous Power Harmonics
2016Co-Authors: M. Ojaghi, N. Yazdandoost, S. GholmohammadzadehAbstract:Harmful impacts of Oil Whirl fault in sleeve bearing can be avoided by early detection of the fault. In this paper, after describing the Oil Whirl fault, an analytic approach is applied to determine frequency of the harmonics produced by the fault in instantaneous power waveform of induction motor. Then, using appropriate air gap function, winding function approach is used for simulating squirrel cage induction motor with bearing Oil Whirl fault. The instantaneous power spectrum, plotted using simulation results, approves creation of the proposed harmonics. These harmonics are also evident in instantaneous power of an induction motor that operates on Oil pipe line, where vibration analysis shows presence of Oil Whirl fault in its bearing. Finally, the most appropriate harmonic as the Oil Whirl fault index is selected using simulation by considering their relative amplitudes as well as their sensitivity to the fault type, fault degree, motor load level and three-phase unbalance of the stator voltages.
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Oil-Whirl Fault Modeling, Simulation, and Detection in Sleeve Bearings of Squirrel Cage Induction Motors
IEEE Transactions on Energy Conversion, 2015Co-Authors: M. Ojaghi, N. YazdandoostAbstract:Bearings are divided into two main categories: rolling bearings and sleeve bearings. The sleeve bearings are normally used in electrical machines above 200-hp rating. In this paper, dynamic modeling and simulation of a squirrel cage induction motor with sleeve bearings under Oil-Whirl fault is performed. The required air gap function under the fault is defined using earlier experimental results. Then, a winding function approach is used for modeling and simulation of the motor with faulty sleeve bearings. Accuracy of the simulation is approved by comparison to the corresponding experimental results. The stator line current harmonics produced by the bearing Oil-Whirl fault are identified, and the best harmonics as the fault index are chosen considering sensitivity of the harmonics to the fault severity, as well as the load level change and supply voltage unbalance. Selected index is used to determine the severity of Oil-Whirl fault in sleeve bearing of an induction motor working in a real production line.
Ling Xiang - One of the best experts on this subject based on the ideXlab platform.
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Multi-fault coupling study of a rotor system in experimental and numerical analyses
Nonlinear Dynamics, 2019Co-Authors: Ling Xiang, Zeqi Deng, Xueyuan GaoAbstract:Multi-fault rotor system is a hot spot in the study of rotor dynamics and fault diagnosis. The present study is aimed to deal with the vibration response and nonlinear behavior of a cracked rotor system with rub-impact supported by sliding bearings. A dedicated experiment is designed to verify the interaction between the several faults for a rotor system. These faults are crack, rub-impact and Oil-film instability. The time domain plot, frequency spectrum and cascade spectra are employed to extract the response features of the rotor system. The numerical investigation is given to compare with the experiment results, which concentrates on the effect of crack depth and stator stiffness on the vibration response and system instability of the multi-fault rotor system. The bifurcation diagrams, frequency spectra, Poincare maps, and cascade spectra are used to analyze the nonlinear coupled behaviors of the multi-fault rotor system. The results from experiment and simulation indicate that the coupling effect exists in the faults of crack, rub-impact and Oil-film instability. The crack interferes with the formation of Oil Whirl, that is, the Oil Whirl is delayed to appear. Moreover, enhancing the stator stiffness can restrain the appearance of the Oil Whirl and simplify the dynamic motion of the system. The study discloses the coupling phenomenon of multi-fault rotor system and presents the response characteristics and nonlinear dynamical behaviors of the interaction between multiple faults for such a rotor-bearing system.
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URAI - Study on nonlinear dynamics of a rotor-bearing system with coupled faults of crack and rub-impact
2016 13th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2016Co-Authors: Ling Xiang, Xueyuan Gao, Yi JiaAbstract:A nonlinear dynamic model is established to analyze the complicated dynamic behaviors of a rotor-bearing system with coupled faults in this paper, where the time-varying crack stiffness, rub-impact force and nonlinear Oil-film force are taken into consideration. The numerical simulation focuses on the effects of crack depth on the onset of instability and nonlinear vibration responses of the rotor-bearing system by using bifurcation diagrams, largest Lyapunov exponent (LLE) and frequency spectrum. The results reveal that crack depth affects the vibration response and instability of the system within varied rotating speed. And the motion of the system with coupled faults shows strong nonlinearity and instability in high speed region. Moreover, the formation of Oil-Whirl is interfered by crack depth, thus, making the Oil-Whirl appear later. There also exists interaction among coupled multiple faults. The research discloses the worthy energy exchange phenomenon of multi-fault system, and contributes to fault diagnosis and vibration control of real rotor-bearing systems.
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Nonlinear dynamics of an asymmetric rotor-bearing system with coupling faults of crack and rub-impact under Oil-film forces
Nonlinear Dynamics, 2016Co-Authors: Ling Xiang, Xueyuan GaoAbstract:The parametric instability of a rotor-bearing system with coupling faults of crack and rub-impact under nonlinear Oil-film force is studied in this paper. A model considering time-varying crack stiffness, rub-impact force and nonlinear Oil-film force is put forward to analyze the complicated nonlinear behaviors of the rotor-bearing system. The numerical simulation focuses on the effects of crack depth and the stator stiffness on the onset of instability and nonlinear responses of the rotor-bearing system by using bifurcation diagrams, Poincare maps, largest Lyapunov exponent and frequency spectrum. The multiple periodic, quasiperiodic and chaotic motions are observed in this study. The results indicate that crack depth and stator stiffness have influences on the vibration and instability of the rotor-bearing system with varied rotating speed. The motion of the system with coupling faults shows strong nonlinearity and instability in high speed region. Moreover, crack depth and stator stiffness interfere with the formation of Oil Whirl, thus, making the Oil Whirl appear later. There also exists interaction among coupling multiple faults. The research discloses the worthy energy exchange phenomenon of multi-fault system and is helpful for fault diagnosis and vibration control of real rotor-bearing systems.
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nonlinear coupled dynamics of an asymmetric double disc rotor bearing system under rub impact and Oil film forces
Applied Mathematical Modelling, 2016Co-Authors: Ling Xiang, Aijun Hu, Yeping Xiong, J T XingAbstract:Abstract The nonlinear dynamic behavior of an asymmetric double-disc rotor-bearing system with interaction between rub-impact and Oil-film forces is addressed in this paper. Using dynamics theory, the mathematical model of an asymmetric double-disc rotor-bearing system is established, considering nonlinear Oil-film force and rub-impact force. The nonlinear Oil-film force model is presented in Reynolds equation, and the rub-impact is assumed with a Hertz contact and a Coulomb friction. The dynamic equations with coupled rub-impact and Oil-film forces are numerically solved using the Runge–Kutta method. Bifurcation diagrams, largest Lyapunov exponent, Poincare maps, and three-dimension spectral plots are employed to analyze the dynamic behavior of the system. The sub-harmonic, multiple periodic, quasi-periodic and chaotic motions are observed in this study. A special phenomenon is occurring that the motion of system becomes simple and the Oil-Whirl is restrained or even removed with an increasing imbalance by magnifying the eccentricity. Another special phenomenon is also occurring that the Oil-Whirl gets diminished or even disappeared with increasing stator stiffness, but the Oil-whip is uninfluenced. The discoveries will have a considerable value as diagnostic tools in settling Oil-film instability. The numerical results show that the nonlinear dynamic behavior of the system varies with the rotational speed and model parameters.
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URAI - Feature analysis of interaction on rub-impact and Oil-film faults for a rotor-bearing system
2015 12th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2015Co-Authors: Ling Xiang, Lanlan HouAbstract:This study deals with experimental investigations where the nonlinear features of an asymmetric double-disc rotor-bearing system are reproduced considering rub-impact and Oil-film instability. A dedicated experimental set-up was designed to validate the interaction between rubs and Oil-firm vibration. The experimental study focuses on the interaction of Oil-Whirl/whip and rub-impact faults, and the results show that the Oil-Whirl is restrained or even removed but the whip is uninfluenced when the rub becomes heavy contact. The results from the experiments indicate that the motion of system becomes simple and the Oil-Whirl gets diminished or even disappeared but the whip keeps unchanged when the eccentricity or the stator stiffness increases. The research discloses the worthy energy exchange phenomenon of multi-fault system, and presents the nonlinear dynamical characteristics of the interaction between rub-impact and Oil-film instability for such a rotor-bearing system.
Kristian Tønder - One of the best experts on this subject based on the ideXlab platform.
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Oil whip-induced wear in journal bearings
The International Journal of Advanced Manufacturing Technology, 2014Co-Authors: Kjell G. Robbersmyr, Herman Olsen, Hamid Reza Karimi, Kristian TønderAbstract:This paper investigates the effect of Oil Whirl and Oil whip in fluid film radial bearings due to possible metallic contact. The degree of metallic contact and thereby wear and tear between rotating shafts and bearing bushes is assessed by measuring electric currents through the Oil film. The current as well as the voltage varied in accordance with the contact ratio between the shaft and bush in the fluid film radial bearing. The gauge signal thus indicates the degree of metallic contact based on the thickness of the Oil film in the load zone. Some experimental results are provided to illustrate that at low normalised loads involving Oil Whirl and Oil whip, no electric current is detected, while high levels of electric current are registered at high load levels when no Oil Whirl or Oil whip occurred. It is therefore concluded that at low loads, Oil Whirl and Oil whip have little influence on wear and tear in a journal bearing.
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Oil whip-induced wear in journal bearings
The International Journal of Advanced Manufacturing Technology, 2014Co-Authors: Kjell G. Robbersmyr, Herman Olsen, Hamid Reza Karimi, Kristian TønderAbstract:Published version of an article in the journal: International Journal of Advanced Manufacturing Technology. Also available from the publisher at: http://dx.doi.org/10.1007/s00170-014-5805-8This paper investigates the effect of Oil Whirl and Oil whip in fluid film radial bearings due to possible metallic contact. The degree of metallic contact and thereby wear and tear between rotating shafts and bearing bushes is assessed by measuring electric currents through the Oil film. The current as well as the voltage varied in accordance with the contact ratio between the shaft and bush in the fluid film radial bearing. The gauge signal thus indicates the degree of metallic contact based on the thickness of the Oil film in the load zone. Some experimental results are provided to illustrate that at low normalised loads involving Oil Whirl and Oil whip, no electric current is detected, while high levels of electric current are registered at high load levels when no Oil Whirl or Oil whip occurred. It is therefore concluded that at low loads, Oil Whirl and Oil whip have little influence on wear and tear in a journal bearing
