Optimization of Journal Bearing Profile for Higher Dynamic Stability Limits

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Rodrigo Nicoletti
Keyword(s):  
Journal Bearing ◽  
Optimization Procedure ◽  
Control Points ◽  
Time Domain Simulation ◽  
Rotating System ◽  
Stability Margins ◽  
Dynamic Coefficients ◽  
The Stability ◽  
Stability Limits ◽  
Improve Stability

This work presents an optimization procedure to find bearing profiles that improve stability margins of rotor-bearing systems. The profile is defined by control points and cubic splines. Stability margins are estimated using bearing dynamic coefficients, and obtained solutions are analyzed as a function of the number of control points and of the Sommerfeld number at optimization. Results show the feasibility of finding shapes for the bearing that significantly improve the stability margins. Some of the obtained solutions overcome the stability margins of conventional bearings, such as the journal bearing and preloaded bearings with 0.5 and 0.67 preload. A time domain simulation of a flexible shaft rotating system supported by such bearings corroborates the results.

Stability Analysis of a Hydrodynamic Journal Bearing With Rotating Herringbone Grooves

2003 ◽  
Vol 125 (2) ◽  
pp. 291-300 ◽  
Author(s):  
G. H. Jang ◽  
J. W. Yoon
Keyword(s):  
Journal Bearing ◽  
Equations Of Motion ◽  
Fourier Series Expansion ◽  
Algebraic Equations ◽  
High Rotational Speed ◽  
Dynamic Coefficients ◽  
Stiffness Coefficients ◽  
Hydrodynamic Journal Bearing ◽  
The Stability ◽  
Herringbone Grooves

This paper presents an analytical method to investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill’s infinite determinant of these algebraic equations. The validity of this research is proved by the comparison of the stability chart with the time response of the whirl radius obtained from the equations of motion. This research shows that the instability of the hydrodynamic journal bearing with rotating herringbone grooves increases with increasing eccentricity and with decreasing groove number, which play the major roles in increasing the average and variation of stiffness coefficients, respectively. It also shows that a high rotational speed is another source of instability by increasing the stiffness coefficients without changing the damping coefficients.

Stability of Flexible Rotors With a LeBlanc Balancer

2011 ◽  
Author(s):  
Leonardo Urbiola-Soto ◽  
Marcelo Lopez-Parra
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Flexible Rotor ◽  
Rotating System ◽  
Stability Behavior ◽  
Piv Technique ◽  
Flexible Rotors ◽  
Image Velocimetry ◽  
The Stability ◽  
Stability Limits

Although the liquid balancer has nearly a century of having been introduced by LeBlanc, little information is available on the dynamic response and stability behavior of this kind of device. Earlier author’s research using a high-speed camera and a Particle Image Velocimetry (PIV) technique showed the existence of a fluid backward traveling wave inside the balancer cavity. This damping phenomenon helps enhance the unbalance response of the rotating system and also raises the stability limits. This paper shows that a flexible rotor employing a LeBlanc balancer has remarkable increase in the threshold speed of instability for aerodynamic cross-coupling and viscous internal friction damping.

The Robust Stability of a Wave Bearing

2005 ◽  
Author(s):  
Nicoleta M. Ene ◽  
Florin Dimofte ◽  
Theo G. Keith ◽  
Robert F. Handschuh
Keyword(s):  
Linear System ◽  
Robust Stability ◽  
Fourth Order ◽  
Journal Bearing ◽  
Critical Mass ◽  
Dynamic Coefficients ◽  
Different Types ◽  
Relative Eccentricity ◽  
The Stability ◽  
Hydrodynamic Wave

The purpose of this paper is to compare the stability of a three wave journal bearing with the stability of a hydrodynamic plain circular journal bearing. The study of the stability of a bearing can be reduced to the study of the stability of a fourth order linear system. In this paper, a perturbation method is used to compute the dynamic coefficients of the bearing. The critical mass is determined at every relative eccentricity, for both the circular hydrodynamic wave bearing and the three wave bearing. The influence of the amplitude of the wave on the stability of the wave bearing is also studied. However, not all the phenomena which affects the bearing’s operation can be taken into account, but it is important that the bearing preserves its stability in face of different types of uncertainty. This property is known as robust stability. In this paper, the robust stability of a bearing is evaluated by determining how great the perturbations of the dynamic coefficients could be so that the bearing remains stable. The robust stability is analyzed using the Kharitonov’s theorem.

A simplified thermohydrodynamic stability analysis of journal bearings

2005 ◽  
Vol 219 (3) ◽  
pp. 225-234 ◽  
Author(s):  
S Singhal ◽  
M. M. Khonsari
Keyword(s):  
Journal Bearing ◽  
Journal Bearings ◽  
Lubricating Oil ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Stiffness Coefficients ◽  
Design Charts ◽  
Operating Region ◽  
Rapid Prediction ◽  
The Stability

This work investigates the stability of a journal bearing system, including the effects of inlet viscosity. Simplified thermohydrodynamic design charts for the rapid prediction of stiffness coefficients, damping coefficients, and threshold speed have been developed. This investigation reveals that the inlet viscosity has a pronounced influence on the bearing dynamic coefficients of the lubricating oil film. This investigation also reveals that it is possible to stabilize a journal bearing either by heating the oil or by cooling the oil depending on the operating region.

Stability of a Squeeze-Film Journal Bearing

1967 ◽  
Vol 89 (3) ◽  
pp. 369-373 ◽  
Author(s):  
J. V. Beck ◽  
C. L. Strodtman
Keyword(s):  
Journal Bearing ◽  
Mathieu Equation ◽  
Squeeze Film ◽  
Infinite Length ◽  
Driving Frequency ◽  
Numerical Techniques ◽  
Variational Techniques ◽  
Regions Of Stability ◽  
The Stability ◽  
Stability Limits

An investigation is made of the regions of stability for a compressible fluid, squeeze-film journal bearing of infinite length. Motion along one axis considered and the resulting dynamic equation is solved two ways: by variational techniques and by numerical techniques. The solution from the variational analysis can be approximated by a Mathieu equation thus showing that instability can occur at one-half the driving frequency. The numerical analysis shows the stability limits in terms of the load, drive amplitude, and dimensionless “mass.” The stability analysis is significant as there appears to be a rather large number of combinations of the parameters for which the squeeze-film journal is not stable. The stability characteristics of a squeeze-film bearing should, therefore, be examined carefully before application.

A Study of the Stability of an Externally-Pressurized Gas-Lubricated Thrust Bearing With a Flexible Damped Support

1978 ◽  
Vol 100 (3) ◽  
pp. 364-368 ◽  
Author(s):  
D. A. Boffey
Keyword(s):  
Feasibility Study ◽  
Equilibrium Position ◽  
Reynolds Equation ◽  
Thrust Bearing ◽  
Dynamic Instability ◽  
Pneumatic Hammer ◽  
Gas Bearings ◽  
Dynamic Coefficients ◽  
The Stability ◽  
Improve Stability

Externally-pressurized gas bearings are prone to a dynamic instability known as pneumatic hammer. This paper examines the possibility of using a flexible damped bearing support to suppress the instability. A circular thrust bearing having a central feed hole and pocket is employed in the feasibility study. The linearized gas film dynamic coefficients are derived using an adaptation of an existing solution to Reynolds equation for a long rectangular bearing. Only stability of the equilibrium position is considered. Results obtained for a support having a stiffness comparable to the stiffness of the gas film show that damping in the support can substantially improve stability.

Linear Stability Analysis of a Tilting-Pad Journal Bearing System

2006 ◽  
Vol 129 (2) ◽  
pp. 348-353 ◽  
Author(s):  
Guang Qiao ◽  
Liping Wang ◽  
Tiesheng Zheng
Keyword(s):  
Linear Stability ◽  
Degrees Of Freedom ◽  
Journal Bearing ◽  
Critical Mass ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Assembly Technique ◽  
The Stability ◽  
Tilting Pad Journal Bearing ◽  
Bearing System

This paper describes a mathematical model to study the linear stability of a tilting-pad journal bearing system. By employing the Newton-Raphson method and the pad assembly technique, the full dynamic coefficients involving the shaft degrees of freedom as well as the pad degrees of freedom are determined. Based on these dynamic coefficients, the perturbation equations including self-excited motion of the rotor and rotational motion of the pads are derived. The complex eigenvalues of the equations are computed and the pad critical mass identified by eigenvalues can be used to determine the stability zone of the system. The results show that some factors, such as the preload coefficient, the pivot position, and the rotor speed, significantly affect the stability of tilting-pad journal bearing system. Correctly adjusting those parameter values can enhance the stability of the system. Furthermore, various stability charts for the system can be plotted.

Evaluation of Dynamic Coefficients of a Two-Lobe Journal Bearing Using an Electrical Analogy Approach

1996 ◽  
Vol 118 (3) ◽  
pp. 657-662 ◽  
Author(s):  
Har Prashad
Keyword(s):  
Journal Bearing ◽  
Operating Conditions ◽  
Dynamic Coefficients ◽  
Electrical Analogy ◽  
Dimensional Parameters ◽  
Capacitive Reactance ◽  
Hydrodynamic Journal Bearing ◽  
The Stability ◽  
Stability Regime ◽  
Stiffness And Damping

A theoretical approach to evaluating capacitance, resistance, capacitive reactance, and impedance of the lower and upper lobes of a two-lobe elliptical hydrodynamic journal bearing under various operating conditions is developed. It is established that the change in capacitance and resistance with the change in eccentricity ratios is nonlinear. The capacitance and resistance, thus determined, are correlated with the dynamic coefficients of bearings using an electrical analogy. It is found that the stiffness and damping coefficients are higher for two-lobe bearings as compared to those of cylindrical bearings having identical dimensional parameters and operating under similar conditions. The analysis may have the potential to diagnose the stability regime of a bearing through the bearing’s electrical parameters. The electrical analogy may be a useful alternative to conventional techniques.

Comparison study of misalignment effect along two perpendicular directions on the stability of rigid rotor-aerostatic journal bearing system

2020 ◽  
Vol 234 (10) ◽  
pp. 1618-1634
Author(s):  
Jianbo Zhang ◽  
Han Zhao ◽  
Donglin Zou ◽  
Na Ta ◽  
Zhushi Rao
Keyword(s):  
Journal Bearing ◽  
Thickness Distribution ◽  
Vertical Direction ◽  
Inertial Force ◽  
Journal Bearings ◽  
Rigid Rotor ◽  
Stability Threshold ◽  
Dynamic Coefficients ◽  
The Stability ◽  
Bearing System

Under misalignment condition, the film thickness distribution of aerostatic journal bearings is changed comparing with condition without misalignment, which results in the change of performances of aerostatic journal bearings. In the paper, the effects of misalignment along two perpendicular directions (along the vertical direction θ y and along the horizontal direction θ x) on the dynamic coefficients and stability thresholds of both critical whirl ratio and critical inertial force calculated by the motion equation of rigid rotor-aerostatic journal bearing system are studied comparatively. The results indicate that the dynamic coefficients, critical whirl ratio, and critical inertial force are more sensitive to θ x compared with θ y. Moreover, the stability threshold of whirl ratio reduces with increasing the misalignment degree, while stability threshold of inertial force increases with increasing the misalignment degree.

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