The Stability of a Flexible Rotor Supported by Circumferentially Fed Journal Bearings

1977 ◽  
Vol 99 (4) ◽  
pp. 469-477 ◽  
Author(s):  
P. Bar-Yoseph ◽  
J. J. Blech
Keyword(s):  
Journal Bearings ◽  
Asymptotically Stable ◽  
Direct Integration ◽  
Flexible Rotor ◽  
Nonlinear Prediction ◽  
Speed Range ◽  
The Stability

The stability of a flexible rotor, perfectly balanced, was investigated theoretically. The rotor is symmetrically supported by circumferentially fed journal bearings. Short and finite bearings were treated. Stability was checked for small and large disturbances. Two methods were employed to treat large disturbances: Direct integration and the slowly varying technique. The nonlinear prediction was tested concurrently with the prediction of the stability charts. It was observed that in certain cases stability can be obtained in the asymptotic and in the unstable regions. Instability was obtained for regions which presumably are asymptotically stable in the entire speed range.

Nonlinear Simulation Analysis and Experiment of Fluid Plain Journal Bearing With Incompressible Fluid

2003 ◽  
Author(s):  
Katsuhisa Fujita ◽  
Atsuhiko Shintani ◽  
Koji Yoshioka ◽  
Kouhei Okuno ◽  
Hiroaki Tanaka ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Incompressible Fluid ◽  
Journal Bearing ◽  
Simulation Analysis ◽  
Journal Bearings ◽  
Stable Region ◽  
Flexible Rotor ◽  
Nonlinear Simulation ◽  
Fluid Forces ◽  
The Stability

Recently, in many areas such as computers and information equipments etc., the fluid journal bearings are required to rotate at higher speed. To satisfy this requirement, the strictly stability analysis of the journal is indispensable. In this paper, we investigate the stability analysis of the dynamic behavior of the fluid plain journal bearing with an incompressible fluid considering the nonlinear terms of fluid forces. The stability analysis is examined by the numerical simulations on each model of a rigid rotor and a flexible rotor. The stable regions by nonlinear analysis are compared with the regions by classical linear analysis. Performing the nonlinear simulation analysis, it becomes clear that there is rather a stable region which amplitude does not grow up abruptly, and this phenomenon can not only be pointed out, but also is judged to be unstable by linear stable analysis. Finally, the experiment using actual bearings is performed and compared with the numerical results.

The Stability of an Elastic Rotor in Journal Bearings With Flexible, Damped Supports

1965 ◽  
Vol 32 (4) ◽  
pp. 911-920 ◽  
Author(s):  
Jorgen W. Lund
Keyword(s):  
Theoretical Analysis ◽  
Dynamic Properties ◽  
Journal Bearings ◽  
Rotor Speed ◽  
Flexible Rotor ◽  
Damping Coefficients ◽  
Oil Whip ◽  
The Stability ◽  
Rotor Stiffness ◽  
Gas Bearing

A theoretical analysis is presented investigating the stability (fractional frequency whirl, “oil whip”) of a symmetrical, flexible rotor supported in journal bearings. The bearings are mounted in flexible, damped supports. The analysis determines the rotor speed at which instability sets in as affected by rotor stiffness, the dynamic properties of the bearing film, and the flexibility and damping of the bearing supports. The analysis is based on the fact that the bearing can be represented by frequency-dependent spring and damping coefficients, and the method by which the coefficients are obtained is described with emphasis on the gas-lubricated bearing. The conclusions are: (a) Rotor and support flexibility by themselves lower the speed at onset of instability; (b) when the bearing support possesses damping in addition to flexibility, the speed at onset of instability can be raised significantly above the threshold speed of a rotor in rigidly mounted bearings. Numerical results are presented in the form of graphs for the plain cylindrical gas bearing.

Control of Stability and the Synchronous Vibration of a Flexible Rotor Supported on Oil-Film Bearings

1985 ◽  
Vol 107 (2) ◽  
pp. 139-144 ◽  
Author(s):  
M. N. Sahinkaya ◽  
C. R. Burrows
Keyword(s):  
Adaptive Control ◽  
Control Strategy ◽  
Open Loop ◽  
Flexible Rotor ◽  
Oil Film ◽  
Oil Whirl ◽  
Speed Range ◽  
Adaptive Control Strategy ◽  
The Stability ◽  
The Relationship

The relationship between eigenvalue loci for the rotor-bearing systems and the onset of instability due to oil-whirl, is utilized to derive an algorithm to control the onset of instability. Implementation of the algorithm is discussed. It is shown how this can be combined with an open-loop adaptive control strategy to ensure the stability of a flexible rotor and also minimize the synchronous vibration throughout the operational speed range.

scholarly journals Stability and Stability Degree of a Cracked Flexible Rotor Supported on Journal Bearings

1993 ◽  
Author(s):  
Meng Guang ◽  
Robert Gasch
Keyword(s):  
Journal Bearings ◽  
Speed Ratio ◽  
Mass Ratio ◽  
Flexible Rotor ◽  
Cracked Rotor ◽  
Unstable Region ◽  
Stability Degree ◽  
Large Influence ◽  
Crack Stability ◽  
The Stability

Abstract This paper investigates the stability and the stability degree of a flexible cracked rotor supported on different kinds of journal bearings. It is found that no matter what kind of bearings is used, the unstable zones caused by rotor crack locate always within the speed ratio 2N(1-△Kξ4)<Ω<2N when gravity parameter Wg > 1.0; and locate always within the speed ratio 2ΩαN(1-△Kξ4)<Ω<2ΩαN when Wg < 0.1, where ΔKξ is the crack stiffness ratio, N = 1, 2, 3, 4, 5 … and Ωα=(1+2α2α)1/2. When 0.1 < Wg < 1.0, there is a region, where no unstable zones caused by rotor crack exist. Outside the crack ridge zones, the rotor crack has almost no influence on system’s stability and stability degree; while within the crack ridge zones, the stability and stability degree depend both on the crack and system’s parameters. In some cases, the system may still be stable even the crack is very large. For small gravity parameter (Wg < 0.1), the mass ratio α has large influence on the position of unstable region, but its influence on the stability degree is small. The influence of fixed Sommerfeld number So on the crack stability degree is small although So has large influence on the stability degree of uncracked rotor.

Experiments on the Stability and Response of a Flexible Rotor in Three Types of Journal Bearings

1982 ◽  
Vol 25 (3) ◽  
pp. 289-298 ◽  
Author(s):  
R. F. Lanes ◽  
R. D. Flack ◽  
D. W. Lewis
Keyword(s):  
Journal Bearings ◽  
Flexible Rotor ◽  
The Stability

scholarly journals Stability and Stability Degree of a Cracked Flexible Rotor Supported on Journal Bearings

1999 ◽  
Vol 122 (2) ◽  
pp. 116-125 ◽  
Author(s):  
G. Meng ◽  
R. Gasch
Keyword(s):  
Journal Bearings ◽  
Speed Ratio ◽  
Stiffness Ratio ◽  
Mass Ratio ◽  
Flexible Rotor ◽  
Cracked Rotor ◽  
Unstable Region ◽  
Stability Degree ◽  
Large Influence ◽  
The Stability

This paper investigates the stability and the stability degree of a cracked flexible rotor supported on different kinds of journal bearings. It is found that no matter what kinds of bearings are used, the unstable zones caused by rotor crack locate always within the speed ratio of 2/N1−ΔKξ /4<Ω<2/N when gravity parameter Wg>1.0; and locate always within the speed ratio of 2Ωα/N1−ΔKξ /4<Ω<2Ωα/N when Wg<0.1, where ΔKξ is the crack stiffness ratio, N=1,2,3,4,5,… and Ωα=1+1/2α1/2. When 0.1<Wg<1.0, there is a region where no unstable zones caused by rotor crack exist. Outside the crack ridge zones, the rotor crack has almost no influence on the system’s stability and stability degree; while within the crack ridge zones, the stability and the stability degree depend both on the crack and the system’s parameters. In some cases, the system may still be stable even though the crack is very large. For small gravity parameter Wg<0.1, the mass ratio α has a large influence on the position of the unstable region, but its influence on the stability degree is small. The influence of fixed Sommerfeld number So on the stability degree of the cracked rotor is small, although So has a large influence on the stability degree of the uncracked rotor. [S0739-3717(00)70502-2]

Nonlinear Dynamics of Flexible Rotors Supported on Journal Bearings—Part I: Analytical Bearing Model

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Mohammad Miraskari ◽  
Farzad Hemmati ◽  
Mohamed S. Gadala
Keyword(s):  
Journal Bearing ◽  
Nonlinear Coefficient ◽  
Journal Bearings ◽  
Flexible Rotor ◽  
Dynamic Coefficients ◽  
Flexible Rotors ◽  
Rotor Bearing ◽  
Bearing Force ◽  
Derivatives Of ◽  
Bearing System

To determine the bifurcation types in a rotor-bearing system, it is required to find higher order derivatives of the bearing forces with respect to journal velocity and position. As closed-form expressions for journal bearing force are not generally available, Hopf bifurcation studies of rotor-bearing systems have been limited to simple geometries and cavitation models. To solve this problem, an alternative nonlinear coefficient-based method for representing the bearing force is presented in this study. A flexible rotor-bearing system is presented for which bearing force is modeled with linear and nonlinear dynamic coefficients. The proposed nonlinear coefficient-based model was found to be successful in predicting the bifurcation types of the system as well as predicting the system dynamics and trajectories at spin speeds below and above the threshold speed of instability.

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