The Effect of Variable Viscosity on the Stability of Plain Journal Bearings and Floating-Ring Journal Bearings

1973 ◽  
Vol 95 (4) ◽  
pp. 447-456 ◽  
Author(s):  
J. L. Nikolajsen
Keyword(s):  
Variable Viscosity ◽  
Practical Interest ◽  
Correct Choice ◽  
Journal Bearings ◽  
Linear Perturbation ◽  
Clearance Ratio ◽  
Design Data ◽  
Oil Whip ◽  
The Stability ◽  
Bearing Behavior

A theoretical analysis including linear perturbation is presented, investigating the stability against fractional frequency whirl (“oil whip”) for a symmetrical rotor supported in plain journal bearings or in floating-ring journal bearings operating with an incompressible lubricant under laminar fluid film flow conditions. In order to improve the conventional theoretical model of the bearing behavior, emphasis is put on the effect on stability of the considerable viscosity gradient which can arise in the bearing film due to film friction. The results are presented in the form of design data diagrams for the two bearing types. In the area of practical interest, the average effect on stability arising from the consideration of the viscosity gradient can be characterized as moderate. Concerning the floating-ring bearing superior stability characteristics are obtained primarily from correct choice of clearance ratio.

Stability of Flexibly Supported Oil Journal Bearings Using Non-Newtonian Lubricants: Linear Perturbation Analysis

2000 ◽  
Vol 123 (3) ◽  
pp. 651-654 ◽  
Author(s):  
K. Raghunandana ◽  
B. C. Majumdar, and ◽  
R. Maiti
Keyword(s):  
Power Law ◽  
Perturbation Analysis ◽  
Perturbation Technique ◽  
Stability Margin ◽  
Journal Bearings ◽  
Diameter Ratio ◽  
Linear Perturbation ◽  
Flexible Support ◽  
The Stability ◽  
Power Law Index

The purpose of this paper is to study the effect of non-Newtonian lubricant on the stability of oil film journal bearings mounted on flexible support using linear perturbation technique. The model of non-Newtonian lubricant developed by Dien and Elrod is taken into consideration. The dynamic co-coefficients are calculated for different values of power law index and length to diameter ratio. These are then used to find stability margin for different support parameters to study the effect of the non-Newtonian lubricant.

Study on the performance of gas foil journal bearings with bump-type shim foil

2020 ◽  
pp. 135065012096900
Author(s):  
Hongyang Hu ◽  
Ming Feng ◽  
Tianming Ren
Keyword(s):  
Dynamic Stability ◽  
Load Capacity ◽  
Practical Interest ◽  
Journal Bearings ◽  
Working Environment ◽  
Foil Thickness ◽  
The Novel ◽  
Improvement Potential ◽  
Stiffness Model ◽  
The Stability

The upscaling of turbomachinery using gas foil journal bearings (GFJBs) is limited because of their limited load capacity and dynamic stability. The improvement potential of shim foil inserted under the bump foil of such bearings is investigated in terms of better bearing performance. The arch height difference Δ hb between the shim foil and bump foil can be zero or not to attain the different effect. By considering the local hardening structural stiffness and an Initial installation clearance due to the shim foil, the static and dynamic characteristics of the novel bearing were calculated through the finite difference method (FDM) and perturbation method, respectively. In the analysis, a modified bump stiffness model considering the variable foil thickness was established, and a 2 D thick plate model was adopted for the top foil. The characteristics of novel GFJB with and without preload were compared with the traditional bearing. The results indicate that the load capacity and direct stiffness of the novel GFJB with shim foil can be increased largely, especially when there is a preload (Δ hb≠0). And the improvement is reinforced as the increment of Δ hb. Moreover, the stability threshold speed ( STS) of rotor supported by the novel GFJBs is enhanced by the preload, which means better stability. In addition, an air compressor test has also been conducted to verify the improved supporting performance of novel bearings. Based on this study it is convinced that the addition of shim foil under a GFJB's bump foil can be of practical interest in the quest of enhanced load capacity and dynamic stability. Moreover, the installation of shim foil is not affected by the working environment and could even be retrofited on the existing GFJBs.

scholarly journals Experiments on the Stability of Various Water-Lubricated Fixed Geometry Hydrodynamic Journal Bearings at Zero Load

1973 ◽  
Vol 95 (4) ◽  
pp. 434-445 ◽  
Author(s):  
F. T. Schuller
Keyword(s):  
Journal Bearings ◽  
Shaft Speed ◽  
Clearance Ratio ◽  
Fractional Frequency ◽  
Trailing Edges ◽  
Minimum Film Thickness ◽  
Maximum Stability ◽  
The Stability ◽  
The One ◽  
Offset Factor

Stability tests were conducted with 3.8 centimeter-(1.5 in.-) diameter, 3.8 centimeter-(1.5 in.-) long, fixed geometry hydrodynamic journal bearings in water at 300 K (80 deg F) with zero load. Five fixed geometry bearings were rated in order of diminishing stability as follows: (1) three-tilted-lobe bearing (offset factor of 1.0), (2) herring-bone-groove bearing, (3) one-segment, three-pad, shrouded Rayleigh-step bearing, (4) three-tilted-lobe journal with axial grooves (offset factor of 1.0) mated with a plain bearing, and (5) three-centrally-lobed bearing with axial grooves (offset factor of 0.5). Maximum stability in lobed bearings and journals is achieved when the lobes are tilted so that the points of minimum film thickness occur near the trailing edges. The herringbone-groove journals had a maximum stability (maximum fractional frequency whirl onset speed) when the groove to ridge clearance ratio was closest to 2.1, as predicted by incompressible flow theory. The one-segment, three-pad shrouded Rayleigh-step bearing configuration was the most stable of the four step-bearing configurations tested. The tilted-lobe journals mated with plain bearings were unique in that, in some tests, the bearings could be run to a shaft speed twice the shaft speed at which initial fractional frequency whirl occurred before any sign of bearing distress was observed.

scholarly journals Experiments on an Ultrastable Gas Journal Bearing

1967 ◽  
Vol 89 (4) ◽  
pp. 433-438 ◽  
Author(s):  
S. B. Malanoski
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Design Data ◽  
Attitude Angle ◽  
Angle Data ◽  
The Stability ◽  
Data Design ◽  
Gas Journal Bearing

Shallow grooving in a herringbone pattern has been proposed to enhance the stability of both gas and liquid-lubricated journal bearings. It has been shown theoretically that this possibility is particularly advantageous for unloaded journal bearings. This paper describes corroborating experiments. The experiments included the running of an unloaded bearing up to speeds of 60,000 rpm and the collection of steady-state load-displacement, attitude angle data at intermediate speeds up to and including 60,000 rpm. No sign of bearing whirl instability was detected. There was good correlation between theoretical and experimental data. Design data for the partially grooved journal bearing is included for future designs.

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.

The Influence of Oil-Film Journal Bearings on the Stability of Rotating Machines

1946 ◽  
Vol 13 (3) ◽  
pp. A211-A220
Author(s):  
A. C. Hagg
Keyword(s):  
Rotational Frequency ◽  
Journal Bearings ◽  
The Self ◽  
Stability Criteria ◽  
Oil Film ◽  
Oil Whip ◽  
Upper Limit ◽  
Excited Vibration ◽  
Tilting Pad ◽  
The Stability

Abstract The self-excited vibration caused by the lubricating films of journal bearings and commonly called oil-film whirl or oil whip is discussed. The upper limit of whirling frequency has been found to be one-half rotational frequency in the general case; actually the phenomenon will manifest itself at a frequency which is invariably below this limit. Stability criteria have been developed for certain common systems in terms of bearing and rotor parameters. The tilting-pad bearing of Michell has been established as a so-called “stable” or “nonwhirling” bearing. This bearing and related types are probably the only oil-film journal bearings which are incapable of exciting oil whip, regardless of the system to which they are applied. Qualitatively the results of the paper appear to be in agreement with observations. In certain cases, results have been substantiated experimentally.

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.

Effect of fluid inertia on the dynamic coefficients and stability of journal bearings

2000 ◽  
Vol 214 (3) ◽  
pp. 229-240 ◽  
Author(s):  
S. K. Kakoty ◽  
B. C. Majumdar
Keyword(s):  
Reynolds Number ◽  
Journal Bearing ◽  
Perturbation Technique ◽  
Journal Bearings ◽  
Linear Perturbation ◽  
Fluid Inertia ◽  
Viscous Forces ◽  
A Value ◽  
The Stability ◽  
Negligible Contribution

In the analysis of hydrodynamic journal bearings the effect of fluid inertia is generally neglected in view of its negligible contribution compared with viscous forces. However, there is a necessity to evaluate its effect at moderate values of the modified Reynolds number. An attempt is made to study the effect of fluid inertia on the stability of journal bearing for a flow in the laminar regime, i.e. for a value of the modified Reynolds number of the order of one. A linear perturbation technique is used to find the dynamic characteristics and stability of a finite journal bearing.

Inertia and Turbulence Effects on Dynamic Characteristics and Stability of Rotor-Bearings Systems

1991 ◽  
Vol 113 (1) ◽  
pp. 58-64 ◽  
Author(s):  
Giuseppe Capone ◽  
Michele Russo ◽  
Riccardo Russo
Keyword(s):  
Reynolds Number ◽  
Dynamic Characteristics ◽  
Stability Limit ◽  
Reynolds Numbers ◽  
Journal Bearings ◽  
Clearance Ratio ◽  
Oil Film ◽  
Turbulence Effects ◽  
The Stability ◽  
Rotor Bearings

The influence of turbulence and inertia of oil film on the dynamic characteristics and stability of rotor-bearings systems is theoretically analyzed for various Reynolds number values. The rotor is assumed to be rigid, symmetrical, balanced, and supported in two identical aligned journal bearings. The fluid film forces are evaluated under the short bearing assumption. Stiffness, damping, and acceleration coefficients, and the stability limit curves are reported versus modified Sommerfeld number for various Reynolds numbers and for radius-clearance ratio R/C = 500.

scholarly journals Steady-state $$\dot{V}{\text{O}}_{2}$$ above MLSS: evidence that critical speed better represents maximal metabolic steady state in well-trained runners

2021 ◽  
Author(s):  
Rebekah J. Nixon ◽  
Sascha H. Kranen ◽  
Anni Vanhatalo ◽  
Andrew M. Jones
Keyword(s):  
Steady State ◽  
Critical Speed ◽  
Lactate Concentration ◽  
Practical Interest ◽  
Blood Lactate Concentration ◽  
Distance Runners ◽  
Severe Intensity ◽  
The Stability ◽  
Trained Runners ◽  
Over Time

AbstractThe metabolic boundary separating the heavy-intensity and severe-intensity exercise domains is of scientific and practical interest but there is controversy concerning whether the maximal lactate steady state (MLSS) or critical power (synonymous with critical speed, CS) better represents this boundary. We measured the running speeds at MLSS and CS and investigated their ability to discriminate speeds at which $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 was stable over time from speeds at which a steady-state $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 could not be established. Ten well-trained male distance runners completed 9–12 constant-speed treadmill tests, including 3–5 runs of up to 30-min duration for the assessment of MLSS and at least 4 runs performed to the limit of tolerance for assessment of CS. The running speeds at CS and MLSS were significantly different (16.4 ± 1.3 vs. 15.2 ± 0.9 km/h, respectively; P < 0.001). Blood lactate concentration was higher and increased with time at a speed 0.5 km/h higher than MLSS compared to MLSS (P < 0.01); however, pulmonary $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 did not change significantly between 10 and 30 min at either MLSS or MLSS + 0.5 km/h. In contrast, $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 increased significantly over time and reached $$\dot{V}{\text{O}}_{2\,\,\max }$$ V ˙ O 2 max at end-exercise at a speed ~ 0.4 km/h above CS (P < 0.05) but remained stable at a speed ~ 0.5 km/h below CS. The stability of $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 at a speed exceeding MLSS suggests that MLSS underestimates the maximal metabolic steady state. These results indicate that CS more closely represents the maximal metabolic steady state when the latter is appropriately defined according to the ability to stabilise pulmonary $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 .

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