Stability Analysis of Rotating Systems Supported by Textured Journal Bearings

2019 ◽  
Vol 142 (3) ◽  
Author(s):  
Douglas Jhon Ramos ◽  
Leandro Ito Ramos ◽  
Gregory Bregion Daniel
Keyword(s):  
Vibration Mode ◽  
Surface Texturing ◽  
Industrial Applications ◽  
Journal Bearings ◽  
Rotating System ◽  
Stability Threshold ◽  
Rotating Systems ◽  
Unstable Vibration ◽  
The Stability ◽  
Volume Method

Abstract Fluid-induced instability in rotating systems due to the presence of hydrodynamic journal bearings consists of an undesirable phenomenon with a considerable destructive potential. Surface texturing of journal bearings is currently investigated as a possible approach to improve the stability characteristics of rotating systems. Thereby, this work aims to evaluate the influence of textured journal bearings in the stability threshold and unstable vibration mode of rotating systems. The classical Reynolds equation is used to model the pressure distribution inside the bearing, being solved by the finite volume method (FVM). The rotating system evaluated in this work is a steam turbine that is modeled using the finite element method (FEM). Numerical results show that textured geometric parameters, i.e., shape, area density, and maximum depth, are capable of changing the stability threshold (for worse or better) as well as the corresponding unstable vibration mode. Moreover, the present study also indicates that a full texturing of journal bearings is desirable to achieve a better improvement in the stability threshold when compared with partial texturing. Based on the results obtained in this work, the textured journal bearings represent a promising and feasible tool to improve the stability conditions of rotating systems in industrial applications.

Estimation of the Damping Matrix in Rotating Machinery for the Calculation of the Stability Threshold Speed

2014 ◽  
Vol 14 (06) ◽  
pp. 1450012 ◽  
Author(s):  
Bram Vervisch ◽  
Kurt Stockman ◽  
Mia Loccufier
Keyword(s):  
Internal Damping ◽  
Gyroscopic Effect ◽  
Rotating System ◽  
Linear Speed ◽  
System Parameters ◽  
Stability Threshold ◽  
Damping Matrix ◽  
Rotating Systems ◽  
Dependent Model ◽  
The Stability

Rotor internal damping is recognized as one of the main causes for instabilities in rotating systems. In a linear speed dependent model, the stability threshold speed can be calculated numerically. However, this threshold depends highly on the modeling choice and mainly on the relation between rotating and nonrotating damping. In this paper, the importance of a well-founded knowledge of the system parameters is highlighted and a method is proposed to estimate the damping of a rotating system not only influenced by the gyroscopic effect but also by rotating damping. With this method, it is possible to reconstruct the physical damping matrix and distinguish between rotating and nonrotating damping. Moreover, the gyroscopic effect can be identified. After a description of the method, a numerical validation is performed.

scholarly journals Stability Analysis of Rotor-Bearing Systems under the Influence of Misalignment and Parameter Uncertainty

2021 ◽  
Vol 11 (17) ◽  
pp. 7918
Author(s):  
Xiaodong Sun ◽  
Kian K. Sepahvand ◽  
Steffen Marburg
Keyword(s):  
Computation Time ◽  
Parametric Uncertainty ◽  
Parameter Uncertainties ◽  
Misalignment Effect ◽  
Stability Threshold ◽  
Rotating Systems ◽  
Rotor Bearing ◽  
Run Up ◽  
The Stability ◽  
The Impact

Stability is a well-known challenge for rotating systems supported by hydrodynamic bearings (HDBs), particularly for the condition where the misalignment effect and the parametric uncertainty are considered. This study investigates the impact of misalignment and inherent uncertainties in bearings on the stability of a rotor-bearing system. The misalignment effect is approximately described by introducing two misaligned angles. The characteristics of an HDB, such as pressure distribution and dynamic coefficients, are calculated by the finite difference method (FDM). The stability threshold is evaluated as the intersection of run-up curve and borderline. Viscosity and clearance are considered as uncertain parameters. The generalized polynomial chaos (gPC) expansion is adopted to quantify the uncertainty in parameters by evaluating unknown coefficients. The unknown gPC coefficients are obtained by using the collocation method. The results obtained by the gPC expansion are compared with those of the Monte Carlo (MC) simulation. The results show that the characteristics of the HDB and the stability threshold are affected by misalignment and parameter uncertainties. As the uncertainty analysis using the gPC expansion is performed on a relatively small number of predefined collocation points compared with the large number of MC samples, the method is very efficient in terms of computation time.

Stability of Multirecess Hybrid-Operating Oil Journal Bearings

1985 ◽  
Vol 107 (1) ◽  
pp. 116-121 ◽  
Author(s):  
Y. S. Chen ◽  
H. Y. Wu ◽  
P. L. Xie
Keyword(s):  
Finite Difference Method ◽  
Dynamic Performance ◽  
Journal Bearings ◽  
Design Parameters ◽  
Stability Threshold ◽  
Damping Coefficients ◽  
Hybrid Bearing ◽  
The Stability ◽  
Stiffness And Damping ◽  
Bearing System

An analysis and a numerical solution using finite difference method to predict the dynamic performance of multirecess hybrid-operating oil journal bearings are presented. The linearized stiffness and damping coefficients of a typical capillary-compensated bearing with four recesses are computed for various design parameters. The corresponding stiffness and the stability threshold of the bearing are then obtained, and the opposite influences of the hydrodynamic action on them are demonstrated. The effect of rotor flexibility on the onset of self-excited whirl is discussed, and a method is given to determine the stability threshold of a rotor-hybrid bearing system.

Short Bearing Analysis Applied to Rotor Dynamics—Part 2: Results of Journal Bearing Response

1976 ◽  
Vol 98 (2) ◽  
pp. 319-329 ◽  
Author(s):  
R. G. Kirk ◽  
E. J. Gunter
Keyword(s):  
Transient Response ◽  
Journal Bearing ◽  
Rotor Dynamics ◽  
Journal Bearings ◽  
Radius Of Curvature ◽  
Extensive Investigation ◽  
Stability Threshold ◽  
Stability Maps ◽  
And Performance ◽  
The Stability

The results of an extensive investigation of the transient response of rotors supported in fluid-film journal bearings is presented in the form of computer generated orbits of rotor motion. The stability of the rotor-bearing system was determined by examination of the system characteristic equation in Part 1. Rotor transient response orbits demonstrate the rotor behavior below and above the stability threshold. The results show the effect of imbalance, steady loading, cyclic unidirectional and rotating loads upon the stability and performance of a short journal bearing. The results are compared to previous investigations and modified stability maps are deduced from the results obtained. The concept of whirl is examined and several plots presented of the instantaneous whirl ratio and radius of curvature versus cycles of motion (of the journal) for the various cases considered. Bearing forces are analyzed and the resulting plots of force versus cycles of motion are presented for selected cases.

Transient Unbalance Response of Four Multilobe Journal Bearings

1980 ◽  
Vol 102 (3) ◽  
pp. 300-306 ◽  
Author(s):  
P. E. Allaire ◽  
D. F. Li ◽  
K. C. Choy
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Transient Response ◽  
Journal Bearings ◽  
Stability Threshold ◽  
Unbalance Response ◽  
Fast Fourier Transform Analysis ◽  
Linearized Stability ◽  
The Stability

This work carries out an analysis of the transient response of four multilobe journal bearings (elliptical, offset, three-lobe, and four-lobe) subject to unbalance both below and above the linearized stability thresholds for the bearings. It extends the work of a previous paper on a balanced rotor in the same four bearing types. Transient orbits, bearing forces, and a numerical fast Fourier transform analysis of the orbits are presented. A comparison of bearing forces above the stability threshold for each bearing indicates that the elliptical bearing has the most violent whirl vibration amplitudes, while the offset bearing exhibits the least amount of subsynchronous vibration.

Stability and Transient Characteristics of Four Multilobe Journal Bearing Configurations

1980 ◽  
Vol 102 (3) ◽  
pp. 291-298 ◽  
Author(s):  
D. F. Li ◽  
K. C. Choy ◽  
P. E. Allaire
Keyword(s):  
Transient Analysis ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Rigid Rotor ◽  
Frequency Content ◽  
Stability Threshold ◽  
Fast Fourier Transform Analysis ◽  
Linearized Stability ◽  
Nonlinear Transient ◽  
The Stability

Multilobe journal bearings are often used to improve the stability response of rotating machinery. Such machines operate near the stability threshold of the bearing-rotor system. This work determines the linearized stability threshold of four multilobe journal bearings: elliptical, offset elliptical, three lobe, and four lobe. A nonlinear transient analysis of a rigid rotor in each of these bearings is carried out above and below the threshold speed. Shaft orbits and bearing forces are calculated. A numerical fast Fourier transform analysis is used to obtain the frequency content of the nonlinear orbit.

scholarly journals Stability analysis of long hydrodynamic journal bearings based on the journal center trajectory

Friction ◽  
2020 ◽  
Author(s):  
Yu Huang ◽  
Haiyin Cao ◽  
Zhuxin Tian
Keyword(s):  
Stability Analysis ◽  
Equilibrium Point ◽  
Journal Bearing ◽  
Stability Boundary ◽  
Initial Point ◽  
Journal Bearings ◽  
Bearing Surface ◽  
Rotating Speed ◽  
Stability Threshold ◽  
The Stability

AbstractIn this study, we observe that there are two threshold speeds (stability threshold speed and second threshold speed) for the long journal bearing, which is different for the short bearing. When the rotating speed is below the stability threshold speed, the stability boundary nearly coincides with the clearance circle, and the journal center gradually returns to the equilibrium point after being released at an initial point. If the rotating speed is between the stability threshold speed and the second threshold speed, after being released at an initial point, the journal center converges to a contour containing the equilibrium point. In this situation, for a higher rotating speed, the corresponding contour is also larger. When the rotating speed exceeds the second threshold speed, the journal gradually moves towards the bearing surface after being released at an initial point.

Linear Stability Analysis of Short Porous Journal Bearings—Use of the Brinkman Model

1995 ◽  
Vol 117 (1) ◽  
pp. 199-202 ◽  
Author(s):  
Jaw-Ren Lin ◽  
Chi-Chuan Hwang
Keyword(s):  
Linear Stability ◽  
Flow Model ◽  
Slip Flow ◽  
Journal Bearings ◽  
Shear Stresses ◽  
Brinkman Model ◽  
Stability Threshold ◽  
Viscous Shear ◽  
Shear Effects ◽  
The Stability

On the basis of a Brinkman model (BM), this paper predicts that the effects of viscous shear stresses on the linear stability of short porous journal bearings are apparent and not negligible. Compared with those of the slip-flow model (SFM) and the Darcy model (DM), the viscous shear effects provide a significant increase in the stability threshold speeds of short porous journal bearings.

On the Influence of the Supply Pressure on the Dynamic Stability of Hybrid Gas Journal Wave Bearings

2005 ◽  
Author(s):  
Florin Dimofte ◽  
Sorin Cioc ◽  
Robert F. Handschuh ◽  
David P. Fleming
Keyword(s):  
Hydrodynamic Instability ◽  
General Rule ◽  
Journal Bearings ◽  
Clearance Ratio ◽  
Stability Threshold ◽  
Supply Pressure ◽  
Bearing Clearance ◽  
Whirling Motion ◽  
Film Instability ◽  
The Stability

Gas journal bearings are very sensitive to the hydrodynamic instability known as subsynchronous whirl motion, especially when they are unloaded. The wave bearing concept can improve the bearing stability, meaning that the wave bearing can run stably up to higher speeds than the plain bearing. In addition, when whirling motion occurs due to the fluid film instability, the orbit of this motion can be contained within the bearing clearance. Another step ahead for improving bearing stability is to pressurize the bearing. Tests were conducted to verify the threshold of subsynchronous whirl motion of bearings with a 35 mm diameter and 30 mm length. Pressurized air is admitted to the bearings through inherent compensated holes located in two planes along the bearing length. Various numbers of holes and diameters were used. The tests were conducted at speeds up to 30,000 rpm and the supply pressure was varied from zero to 0.14 MPa. The pressure was measured within a 2% precision. Two values for the wave amplitude to bearing clearance ratio were used. Pressurizing the bearing with 0.14 MPa can make the bearing run stably up to a speed of 20,000 rpm, unlike an unpressurized bearing that can experience subsynchronous motion at speeds less than 1,000 rpm. It was found that the supply pressure has a strong stabilizing effect. As a general rule, a 10% change of the value of the supply pressure can modify the stability threshold speed with more than 1000 rpm.

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