Stability-Optimized Clearance Configuration of Fluid-Film Bearings

2006 ◽  
Vol 129 (1) ◽  
pp. 106-111 ◽  
Author(s):  
Koichi Matsuda ◽  
Shinya Kijimoto ◽  
Yoichi Kanemitsu
Keyword(s):  
Fourier Series ◽  
Load Capacity ◽  
Fluid Film ◽  
Eccentricity Ratio ◽  
Rotating Speed ◽  
Fluid Film Bearings ◽  
Wide Range ◽  
Jeffcott Rotor ◽  
The Stability ◽  
Frequency Ratios

The whirl instability occurs at higher rotating speeds for a full circular fluid-film journal bearing, and many types of clearance configuration have been proposed to solve this instability problem. A clearance configuration of fluid-film journal bearings is optimized in a sense of enhancing the stability of the full circular bearing at high rotational speeds. A performance index is chosen as the sum of the squared whirl-frequency ratios over a wide range of eccentricity ratios, and a Fourier series is used to represent an arbitrary clearance configuration of fluid-film bearings. An optimization problem is then formulated to find the Fourier coefficients to minimize the index. The designed bearing has a clearance configuration similar to that of an offset two-lobe bearing for smaller length-to-diameter ratios. It is shown that the designed bearing cannot destabilize the Jeffcott rotor at any high rotating speed for a wide range of eccentricity ratio. The load capacity of the designed bearings is nearly in the same magnitude as that of the full circular bearing for smaller length-to-diameter ratios. The whirl-frequency ratios of the designed bearing are very sensitive to truncating higher terms of the Fourier series for some eccentricity ratio. The designed bearings successfully enhance the stability of a full circular bearing and are free from the whirl instability.

Stability-Optimized Clearance Configuration of Fluid-Film Journal Bearings

2005 ◽  
Author(s):  
Koichi Matsuda ◽  
Yoichi Kanemitsu ◽  
Shinya Kijimoto
Keyword(s):  
Optimization Problem ◽  
Journal Bearings ◽  
Fluid Film ◽  
Rotating Speed ◽  
Fluid Film Bearings ◽  
Arbitrary Configuration ◽  
Wide Range ◽  
Jeffcott Rotor ◽  
The Stability ◽  
Frequency Ratios

A clearance configuration of fluid-film journal bearings is optimized in a sense of enhancing the stability of a full circular bearing at high rotational speeds. A performance index is chosen as the sum of the squared whirl-frequency ratios over a wide range of eccentricity ratios, and a Fourier series is used to represent an arbitrary configuration of fluid-film bearings. An optimization problem is then formulated to find the Fourier coefficients to minimize the index. The whirl-frequency ratio is inversely proportional to the stability threshold speeds of a Jeffcott rotor. The short bearing approximation is used to simplify a mathematical model that describes a pressure distribution developed in a fluid-film bearing. The designed bearing cannot destabilize the Jeffcott rotor at any high rotating speed subject to the short-bearing assumption and significantly reduces the size of the unstable region for a finite-length bearing with a small length-to-diameter ratio.

scholarly journals Improvement of Tilting-Pad Journal Bearing Operating Characteristics by Application of Eddy Grooves

Lubricants ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 18
Author(s):  
Eckhard Schüler ◽  
Olaf Berner
Keyword(s):  
High Speed ◽  
Journal Bearing ◽  
Load Capacity ◽  
Fluid Film ◽  
Operating Characteristics ◽  
Fluid Film Bearings ◽  
Tilting Pad ◽  
Bearing Load ◽  
Bearing Loads ◽  
Tilting Pad Journal Bearing

In high speed, high load fluid-film bearings, the laminar-turbulent flow transition can lead to a considerable reduction of the maximum bearing temperatures, due to a homogenization of the fluid-film temperature in radial direction. Since this phenomenon only occurs significantly in large bearings or at very high sliding speeds, means to achieve the effect at lower speeds have been investigated in the past. This paper shows an experimental investigation of this effect and how it can be used for smaller bearings by optimized eddy grooves, machined into the bearing surface. The investigations were carried out on a Miba journal bearing test rig with Ø120 mm shaft diameter at speeds between 50 m/s–110 m/s and at specific bearing loads up to 4.0 MPa. To investigate the potential of this technology, additional temperature probes were installed at the crucial position directly in the sliding surface of an up-to-date tilting pad journal bearing. The results show that the achieved surface temperature reduction with the optimized eddy grooves is significant and represents a considerable enhancement of bearing load capacity. This increase in performance opens new options for the design of bearings and related turbomachinery applications.

The Lower Bound of the Stability Threshold Speed of a Flexible Rotor System in Fluid-Film Bearings

1989 ◽  
Vol 111 (3) ◽  
pp. 351-353
Author(s):  
Wen Zhang
Keyword(s):  
Lower Bound ◽  
Theoretical Foundation ◽  
Simple Approach ◽  
Rotor System ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Stability Threshold ◽  
Fluid Film Bearings ◽  
Single Disk ◽  
The Stability

The paper is devoted to the estimation of the lower bound of the stability threshold speed (STS) of a flexible rotor system supported in fluid-film bearings. It is proved theoretically that the STS of any multi-degree-of-freedom flexible rotor system is always higher than the STS of the corresponding equivalent single disk rotor. The conclusion offers us a simple approach to estimate the STS of any actual rotor system and provides a theoretical foundation for the approach.

Stability Analysis of a Simple Strut with Elastic Springs Through Sensitivity Surfaces and Gradients

2018 ◽  
Vol 18 (12) ◽  
pp. 1850161
Author(s):  
Mario Uroš ◽  
Damir Lazarević ◽  
Marija Demšić ◽  
Josip Atalić
Keyword(s):  
Load Capacity ◽  
Equilibrium Points ◽  
Elastic Stability ◽  
Initial Position ◽  
System Of Nonlinear Equations ◽  
Static System ◽  
Algebraic Equations ◽  
Wide Range ◽  
The Stability ◽  
Potential Energy Method

The global elastic stability of a strut supported by three inclined springs is studied using the exact displacement geometry. The discrete phenomenological model in the theory of stability, described by Thompson and Gaspar, exhibits different postbuckling behaviors, depending on the initial geometry for large imperfections, and this has various applications in engineering. Using the total potential energy method, a system of nonlinear algebraic equations is derived for the nondissipative system. The arc length method is adopted to solve the system of nonlinear equations, considering the stability of equilibrium points at each position, while detecting and traversing the critical points with the possibility of intervention. The characteristic equilibrium paths and their corresponding trajectories are shown and compared with the asymptotic solutions at the first critical point. A parametric analysis is performed, and sensitivity surfaces are constructed for several initial positions of the springs, represented by the initial angle in the horizontal plane. A wide range of independent imperfections with large amplitudes in two directions is considered. The concept of load capacity gradient functions of sensitivity surfaces is introduced and used to qualitatively and quantitatively analyze the stability behavior of the system located far away from the initial position. A few interesting observations and conclusions are obtained from the sensitivity analysis of a simple strut in the postcritical region. The critical combinations of imperfections for each static system are determined through analysis of the gradients. Further, the “stable” and “unstable” regions of the sensitivity surfaces are identified, with some observations made. Finally, the applications of load capacity gradient functions in structural optimization and form findings are reviewed.

Effect of Bearing Profile on the Stability of Statically Indeterminate Rotor Bearing Systems

2007 ◽  
Author(s):  
N. S. Feng ◽  
E. J. Hahn
Keyword(s):  
Dynamic Characteristics ◽  
Rotating Machinery ◽  
Fluid Film ◽  
System Stability ◽  
Fluid Film Bearings ◽  
Flexible Rotors ◽  
Rotor Bearing ◽  
The Stability

The stability of rotating machinery consisting of flexible rotors supported by fluid film bearings is significantly affected by the dynamic characteristics of the bearings and in particular, the bearing profiles as well as the bearing reaction loads, which, in statically indeterminate systems, are in turn strongly influenced by the relative transverse alignment of the bearings. Using a simple four bearing statically indeterminate model, it is shown that relatively simple variants of the circular bearings, viz. elliptic and 2-pad offset bearings display better system stability characteristics systems in aligned situations and are also more likely to be stable in misaligned situations.

Development of a High Speed Gas Bearing Test Rig to Measure Rotordynamic Force Coefficients

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
J. Jeffrey Moore ◽  
Andrew Lerche ◽  
Timothy Allison ◽  
David L. Ransom ◽  
Daniel Lubell
Keyword(s):  
High Speed ◽  
High Amplitude ◽  
Fluid Film ◽  
Test Rig ◽  
Force Coefficient ◽  
Gas Bearings ◽  
Foil Bearings ◽  
Fluid Film Bearings ◽  
Wide Range ◽  
Gas Bearing

The use of gas bearings has increased over the past several decades to include microturbines, air cycle machines, and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional bearings, such as rolling element or oil lubricated fluid film bearings, including longer life, ability to use the process fluid, no contamination of the process with lubricants, accommodating high shaft speeds, and operation over a wide range of temperatures. Unlike fluid film bearings that utilize oil, gas lubricated bearings generate very little damping from the gas itself. Therefore, successful bearing designs such as foil bearings utilize damping features on the bearing to improve the damping generated. Similar to oil bearings, gas bearing designers strive to develop gas bearings with good rotordynamic stability. Gas bearings are challenging to design, requiring a fully coupled thermo-elastic, hydrodynamic analysis including complex nonlinear mechanisms such as Coulomb friction. There is a surprisingly low amount of rotordynamic force coefficient measurement in the literature despite the need to verify the model predictions and the stability of the bearing. This paper describes the development and testing of a 60,000 rpm gas bearing test rig and presents measured stiffness and damping coefficients for a 57 mm foil type bearing. The design of the rig overcomes many challenges in making this measurement by developing a patented, high-frequency, high-amplitude shaker system, resulting in excitation over most of the subsynchronous range.

Development of a High Speed Gas Bearing Test Rig to Measure Rotordynamic Force Coefficients

2010 ◽  
Author(s):  
J. Jeffrey Moore ◽  
Andrew Lerche ◽  
Timothy Allison ◽  
David L. Ransom ◽  
Daniel Lubell
Keyword(s):  
High Speed ◽  
High Amplitude ◽  
Fluid Film ◽  
Test Rig ◽  
Force Coefficient ◽  
Gas Bearings ◽  
Foil Bearings ◽  
Fluid Film Bearings ◽  
Wide Range ◽  
Gas Bearing

The use of gas bearings has increased over the last several decades to include microturbines, air cycle machines, and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional bearings, such as rolling element or oil lubricated fluid film bearings, including longer life, ability to use the process fluid, no contamination of the process with lubricants, accommodating high shaft speeds, and operation over a wide range of temperatures. Unlike fluid film bearings that utilize oil, gas lubricated bearings generate very little damping from the gas itself. Therefore, successful bearing designs such as foil bearings utilize damping features on the bearing to improve the damping generated. Similar to oil bearings, gas bearing designers strive to develop gas bearings with good rotordynamic stability. Gas bearings are challenging to design requiring a fully coupled thermo-elastic, hydrodynamic analysis including complex non-linear mechanisms such as Coulomb friction. There is a surprisingly low amount of rotordynamic force coefficient measurement in the literature despite the need to verify the model predictions and the stability of the bearing. This paper describes the development and testing of a 60,000 rpm gas bearing test rig and presents measured stiffness and damping coefficients for a 57 mm foil type bearing. The design of the rig overcomes many challenges in making this measurement by developing a patented, high-frequency, high-amplitude shaker system resulting in excitation over most of the subsynchronous range.

Reliability Improvement of Rotor Supports by Combining Rolling-Element Bearings and Fluid-Film Bearings

2014 ◽  
Vol 630 ◽  
pp. 188-198 ◽  
Author(s):  
Roman Polyakov ◽  
Leonid Savin ◽  
Denis Shutin
Keyword(s):  
Load Capacity ◽  
Life Time ◽  
Performance Characteristics ◽  
Fluid Film ◽  
Rolling Element Bearing ◽  
Rolling Element Bearings ◽  
Advantages And Disadvantages ◽  
Fluid Film Bearings ◽  
Rolling Element ◽  
Unit Increase

Reliability of rotating machinery is determined to a considerable degree by the bearing units. For several applications the requirements in rotation speed, bearing load and maximal vibration level are so extreme that neither rolling-element bearings nor fluid-film bearings could provide necessary performance characteristics during all regimes of operation. Hybrid bearings, which are a combination of rolling-element and fluid-film bearings, can improve performance characteristics and reliability of the rotor-bearing systems. The aim of this work is to analyze the advantages and disadvantages of the hybrid bearings. Known real applications of hybrid bearings are discussed. Analysis shows that depending on the application different hybrid bearing types could improve dynamic characteristics and life time of the bearing unit, increase load capacity and DN limit of the rolling-element bearing.

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