Active Self-Excited Vibration Elimination of Rotating Machine With an Electromagnetic Exciter

2009 ◽  
Author(s):  
Chen-Chao Fan ◽  
Min-Chun Pan
Keyword(s):  
Journal Bearings ◽  
Rotor System ◽  
Stable Method ◽  
Rotating Machine ◽  
Oil Whip ◽  
Control Scheme ◽  
Oil Whirl ◽  
Excited Vibration ◽  
Load Carrying ◽  
Auxiliary Device

Journal bearings are commonly used in large rotary machineries because they have excellent mechanical and geometric properties as well as large load-carrying capacities. Nevertheless, the oil whirl and oil whip instabilities limit their applications due to their insufficient stiffness at high running speeds. This paper presents a method to increase the stiffness of a rotating machine using an electromagnetic exciter (EE), which can raise the threshold of instability of the rotating machine and eliminate fluid-induced instability. The EE is a controllable auxiliary device that can provide additional stiffness to the bearings to increase the operating ranges of a rotating machine, while the journal bearings act as load-carrying devices. Together, the EE complements the JB to stiffen the rotor system and raise the threshold of instability. A simple control scheme is used to calculate the amount of supplemental stiffness supplied by the EE. The experimental results demonstrate that the oil whirl and oil whip instabilities of the rotating machine can be eliminated effectively, even at higher running speeds. The advantage of the EE is to offer a faster, more stable method to eliminate fluid-induced instability.

Controlling Journal Bearing Instability Using Active Magnetic Bearings

2007 ◽  
Author(s):  
A. El-Shafei ◽  
A. S. Dimitri
Keyword(s):  
Journal Bearing ◽  
Magnetic Bearing ◽  
Journal Bearings ◽  
Active Magnetic Bearing ◽  
Rotating Speed ◽  
Damping Characteristics ◽  
Oil Whip ◽  
Novel Approach ◽  
Oil Whirl ◽  
Load Carrying

Journal Bearings are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, Journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the Journal bearing (JB) instability. An Active Magnetic Bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the Journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device, and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.

Controlling Journal Bearing Instability Using Active Magnetic Bearings

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
A. El-Shafei ◽  
A. S. Dimitri
Keyword(s):  
Journal Bearing ◽  
Magnetic Bearing ◽  
Journal Bearings ◽  
Active Magnetic Bearing ◽  
Rotating Speed ◽  
Damping Characteristics ◽  
Oil Whip ◽  
Novel Approach ◽  
Oil Whirl ◽  
Load Carrying

Journal bearings (JBs) are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the journal bearing instability. An active magnetic bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: Rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.

Some Experiments on Oil Whirl and Oil Whip

2004 ◽  
Author(s):  
A. El-Shafei ◽  
S. H. Tawfick ◽  
M. S. Raafat ◽  
G. M. Aziz
Keyword(s):  
Twentieth Century ◽  
Critical Speed ◽  
Journal Bearings ◽  
Flexible Rotor ◽  
Angular Misalignment ◽  
Oil Whip ◽  
Early Twentieth Century ◽  
Oil Whirl

The oil whirl and oil whip phenomena are well known since the early twentieth century. However, there is a lot of confusion on the parameters that affect the onset of instability. In this study, we investigate the onset of instability on a flexible rotor mounted on two plain cylindrical journal bearings. The rotor is run through the first critical speed, the instability, and the second critical speed. Tests are conducted at various unbalance levels, pressures, and misalignment conditions on the coupling. It is shown that, by far, the misalignment of the coupling is the parameter that is most effective on the onset of instability. In particular angular misalignment resulted in the smoothest rotor response.

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.

Stabilizing Hydrodynamic Bearing Oil Whip With μ-Synthesis Control of an Active Magnetic Bearing

2015 ◽  
Author(s):  
Alexander H. Pesch ◽  
Jerzy T. Sawicki
Keyword(s):  
Rotation Speed ◽  
Stability Limit ◽  
Magnetic Bearing ◽  
Active Magnetic Bearing ◽  
Related Phenomenon ◽  
Test Rig ◽  
Hydrodynamic Bearing ◽  
Oil Whip ◽  
Oil Whirl ◽  
Excited Vibration

Oil whip is a self-excited vibration in a hydrodynamic bearing which occurs when the rotation speed is above approximately twice the first natural frequency. Because of this, the oil whip phenomenon limits the operational speed of a rotor system on hydrodynamic bearings. Below the oil whip threshold, the related phenomenon of oil whirl can cause large vibrations at frequencies below half the rotation speed. A method is presented for stabilizing oil whip and oil whirl in a hydrodynamic bearing with an active magnetic bearing (AMB). The AMB controller is designed with μ-synthesis model-based robust control utilizing the Bently-Muszynska fluid film bearing model, which predicts the unstable phenomena. Therefore, the resulting AMB controller stabilizes the natural instability in the hydrodynamic bearing. Rotor speed is taken into account by use of a parametric uncertainty such that the method is robust to changes in running speed. The proposed method is demonstrated on an experimental hydrodynamic bearing test rig. Details of the test rig and implementation of the AMB controller design are presented. Waterfall plots for the controlled and uncontrolled system are presented which demonstrate the improved stability limit.

Experimental Investigation of the Effect of Angular Misalignment on the Instability of Plain Journal Bearings

2009 ◽  
Author(s):  
Aly El-Shafei ◽  
Sameh H. Tawfick ◽  
Mokhtar O. A. Mokhtar
Keyword(s):  
Journal Bearings ◽  
Displacement Sensor ◽  
Maximum Speed ◽  
Test Rig ◽  
Angular Misalignment ◽  
Vibration Displacement ◽  
Oil Whip ◽  
Fluid Film Bearings ◽  
Oil Whirl ◽  
Overall Stability

The effect of angular misalignment of plain journal bearings on the oil whirl and oil whip phenomena was investigated using a test rig comprising a flexible one inch diameter shaft supported on two cylindrical fluid film bearings. A matrix of experiments was designed where a precisely controlled angular misalignment between the shaft and the drive end, the non-drive end, or both bearings was induced. In each case we measure the onset of oil whirl and/or the onset of oil whip and the maximum speed that the test rig can reach before reaching a maximum vibration displacement of 1 mm at the location of the displacement sensor. The results show clearly that the angular misalignment of the bearings with respect to the shaft help delay the onset of oil whip from 3200 rpm to 4500 rpm in some cases. An interesting and new observation was the effect of the configuration of the misalignment on the overall stability characteristics. In particular, when the two bearings were misaligned in the same direction such that the two misaligned bearing planes were parallel to each other the onset of instability was more delayed and the overall operation was smoother.

Numerical and experimental analysis of the rotor—bearing—seal system

2008 ◽  
Vol 222 (8) ◽  
pp. 1435-1441 ◽  
Author(s):  
X Y Shen ◽  
J H Jia ◽  
M Zhao ◽  
J P Jing
Keyword(s):  
Finite Element ◽  
Labyrinth Seal ◽  
Rotor System ◽  
Equivalent Model ◽  
Stable Region ◽  
The Finite Element Method ◽  
Oil Whip ◽  
Oil Whirl ◽  
Rotor Bearing ◽  
Set Up

The rotor—bearing—seal system is simulated by a model consisting of the rotor, the bearing, the foundation, and the labyrinth seal. Governing equations are set up theoretically using the finite-element method. The equivalent model of the bearing—foundation support system is analysed. Forces from the bearing—foundation support and gas-excited forces in the labyrinth seal are imposed in the finite-element equations. Then an experimental rotor—bearing—seal device is designed and many tests are carried out. The Bode, orbit, and waterfall plots are all constructed from the experimental data. An experimental rotor system is studied using the developed equations. Theoretical results from the developed model are in agreement with the ones from the experiment. Analysis proves that although the gas-excited force in the labyrinth seal can improve the stable region of the rotor—bearing—seal system, it makes the rotor vibrate more violently and initiates destructive impacts within the rotor system when the rotor running speed reaches a certain level. Oil whirl and oil whip of journal bearings are found in both the theoretical calculation and the experiment.

Self-Excited Vibration of Statically Unloaded Pads in Tilting-Pad Journal Bearings

1983 ◽  
Vol 105 (3) ◽  
pp. 377-383 ◽  
Author(s):  
M. L. Adams ◽  
S. Payandeh
Keyword(s):  
Journal Bearing ◽  
Nonlinear Dynamic Analysis ◽  
Journal Bearings ◽  
Practical Significance ◽  
Oil Whip ◽  
Excited Vibration ◽  
Tilting Pad ◽  
Close Relationship ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings

A time-transient nonlinear dynamic analysis is presented to study the motion of statically unloaded journal-bearing tilting pads. The major finding is that unloaded pads can exhibit a strong sub-synchronous self-excited vibration. The frequency of this periodic motion is somewhat below half the rotational speed and bears a close relationship to self-excited oil-whip vibration of rotors on lightly loaded non-tilting pad journal bearings. The identification of this type of self-excited pad vibration has practical significance to the solution of problems in applications involving damage to unloaded pads. A comprehensive parametric study is presented and shows which tilting-pad journal bearing parameters are significant to self-excited pad vibration and its elimination.

Some Experiments on Oil Whirl and Oil Whip

2004 ◽  
Vol 129 (1) ◽  
pp. 144-153 ◽  
Author(s):  
A. El-Shafei ◽  
S. H. Tawfick ◽  
M. S. Raafat ◽  
G. M. Aziz
Keyword(s):  
Twentieth Century ◽  
Critical Speed ◽  
Journal Bearings ◽  
Flexible Rotor ◽  
Angular Misalignment ◽  
Oil Whip ◽  
Early Twentieth Century ◽  
Oil Whirl

The oil whirl and oil whip phenomena have been well known since the early twentieth century. However, there is a lot of confusion on the parameters that affect the onset of instability. In this study, we investigate the onset of instability on a flexible rotor mounted on two plain cylindrical journal bearings. The rotor is run through the first critical speed, the instability, and the second critical speed. Tests are conducted at various unbalance levels, pressures, and misalignment conditions on the coupling. It is shown that, by far, the misalignment of the coupling is the parameter that is most effective on the onset of instability. In particular angular misalignment resulted in the smoothest rotor response.

scholarly journals Frequency Enhancement of Oil Whip and Oil Whirl in a Ferrofluid–Lubricated Hydrodynamic Bearing–Rotor System by Magnetic Field with Permanent Magnets

2018 ◽  
Vol 8 (9) ◽  
pp. 1687
Author(s):  
Liao-Yong Luo ◽  
Yi-Hua Fan ◽  
Jyh-Haw Tang ◽  
Ting-Yu Chen ◽  
Nai-Rong Zhong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Permanent Magnets ◽  
Journal Bearing ◽  
Rotor System ◽  
Hydrodynamic Bearing ◽  
System A ◽  
Oil Whip ◽  
Oil Whirl ◽  
Hydrodynamic Journal Bearing ◽  
Whirl Speed

The article describes the effect of a magnetic field applied to a ferrofluid–lubricated hydrodynamic journal bearing–rotor system. A rotor with a single journal bearing in one end was built to be the test rig. The experimental results showed that 3 to 8 permanent magnets, arranged by different methods, can all increase the instability threshold of the oil bearing. Especially, the magnetic field formed by eight magnets has the optimal effect. The whirl speed and the whip speed can be increased from 3024 rpm to 4480 rpm, and from 3184 rpm to 5268 rpm.

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