Prediction of Dry-Friction Whirl and Whip Between a Rotor and a Stator

2006 ◽  
Author(s):  
Dara W. Childs ◽  
Avijit Bhattacharya
Keyword(s):  
Friction Force ◽  
Dry Friction ◽  
Coulomb Force ◽  
Test Results ◽  
Jeffcott Rotor ◽  
Transient Simulations ◽  
Force Direction ◽  
Function Definition ◽  
Multi Mode ◽  
Coulomb Friction Force

This paper addresses recent test results for dry-friction whip and whirl. Authors of these publications suggest that predictions from Black’s 1968 paper are deficient in predicting their observed transition speeds from whirl to whip and the associated precession frequencies of whirl and whip motion. Predictions from Black’s simple Jeffcott-rotor/point-mass stator are cited. This model is extended here to a multi-mode rotor and stator model with an arbitrary axial location for rotor-stator rubbing. Predictions obtained from this new model are quite close to experimental observations in terms of the transition from whip to whirl and observed precession frequencies. Paradoxically, nonlinear numerical simulations using Black’s model fail to produce the whirl and whip solutions. The Coulomb friction force in Black’s model has a fixed direction, and Bartha showed in 2000 that by making the friction-force direction depend on the relative sliding velocity, nonlinear simulations would produce the predicted whirl solutions. He also showed that Black’s proposed whip solution at the upper precession-frequency transition from whirl to whip was unstable. Results presented here show that Black’s whirl solutions are unstable for all whirl precession frequencies, not just the whirl-whip transition frequency. The multi-mode extension of Black’s model predicts a complicated range of whirl and whip possibilities; however, nonlinear time-transient simulations (including the sgn function definition for the Coulomb force) only produce the initial whirl precession range, the initial whirl-whip transition, and the initial whip frequency. Simulation results for these values agree well with predictions. However, none of the predicted higher-frequency whirl results are obtained. Also, the initial whip frequency persists to quite high running speeds and does not (as predicted) transition to higher frequencies. Hence, despite its deficiencies, correct and very useful predictions are obtained from a reasonable extension of Black’s model.

Prediction of Dry-Friction Whirl and Whip Between a Rotor and a Stator

2007 ◽  
Vol 129 (3) ◽  
pp. 355-362 ◽  
Author(s):  
Dara W. Childs ◽  
Avijit Bhattacharya
Keyword(s):  
Friction Force ◽  
Dry Friction ◽  
Coulomb Friction ◽  
Coulomb Force ◽  
Test Results ◽  
Jeffcott Rotor ◽  
Transient Simulations ◽  
Force Direction ◽  
Function Definition ◽  
Coulomb Friction Force

This paper addresses recent test results for dry-friction whip and whirl. Authors of these publications suggest that predictions from Black’s 1968 paper (J. Mech. Eng. Sci., 10(1), pp. 1–12) are deficient in predicting their observed transition speeds from whirl to whip and the associated precession frequencies of whirl and whip motion. Predictions from Black’s simple Jeffcott-rotor/point-mass stator are cited. This model is extended here to a multimode rotor and stator model with an arbitrary axial location for rotor-stator rubbing. Predictions obtained from this new model are quite close to experimental observations in terms of the transition from whip to whirl and observed precession frequencies. Paradoxically, nonlinear numerical simulations using Black’s model fail to produce the whirl and whip solutions. The Coulomb friction force in Black’s model has a fixed direction, and Bartha showed in 2000 (“Dry Friction Backward Whirl of Rotors,” Dissertation, THE No. 13817, ETH Zurich) that by making the friction-force direction depend on the relative sliding velocity, nonlinear simulations would produce the predicted whirl solutions. He also showed that Black’s proposed whip solution at the upper precession-frequency transition from whirl to whip was unstable. The multimode extension of Black’s model predicts a complicated range of whirl and whip possibilities; however, nonlinear time-transient simulations (including the sgn function definition for the Coulomb force) only produce the initial whirl precession range, initial whirl-whip transition, and initial whip frequency. Simulation results for these values agree well with predictions. However, none of the predicted higher-frequency whirl results are obtained. Also, the initial whip frequency persists to quite high running speeds and does not (as predicted) transition to higher frequencies. Hence, despite its deficiencies, correct and very useful predictions are obtained from a reasonable extension of Black’s model.

Tribology research of the turned zirconium-dioxide ceramics

2012 ◽  
Vol 3 (3) ◽  
pp. 181-190
Author(s):  
G. Fledrich ◽  
R. Keresztes ◽  
L. Zsidai
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Dry Friction ◽  
Zirconium Dioxide ◽  
Steel Specimen ◽  
Friction Condition ◽  
Normal Direction ◽  
Basic Material ◽  
Series Production ◽  
Ceramic Specimen

The zirconium dioxide as basic material is suitable to machine by tool with regular edge derivingfrom lower ceramic hardness and from other characteristics so in case of piece production or small – andmedium series production, at quick prototype production can become potential material alike. The aims tocompare the arising frictional characteristics in case of dry friction condition in case of ceramic – steelsurface pairs machined with different sets. We have developed for an equipment to carry out tribologicaltests. During the test we pressure the steel counter face with determined normal direction force thecasing surface of the rotating ceramic specimen and in the meantime we measure the value of the frictionforce with force meter cell. We have calculated the friction coefficient characterizing the system from thenormal direction force and the friction force as well as we measured the wear of the steel specimen andits deformation.

A General Model for Two-Point Contact Dry-Friction Whip and Whirl: Further Advancements and Experimental Test Results

2015 ◽  
Author(s):  
Jason C. Wilkes ◽  
Tim Allison
Keyword(s):  
Experimental Test ◽  
General Model ◽  
Dry Friction ◽  
Point Contact ◽  
Current Work ◽  
Test Results ◽  
Air Bearings ◽  
Test Rig ◽  
Single Location ◽  
Arbitrary Phase

Numerous papers have investigated the behavior of dry-friction whip and whirl; most of them consider contact between a rotor and stator at a single location. For rotors running on multiple magnetic bearings, air bearings, or bushings, equipment failure may result in rub at more than one location. For these cases, it is important to have an analytical model that characterizes possible regions of two-point contact dry-friction whip and whirl. The current work presents a general model to predict possible whirl regions for multi-contact dry-friction whip and whirl, allowing for an arbitrary phase between contact locations. In theory this method can be applied to more than two contact locations; however, a two-point contact example case is developed and compared to results from an experimental test rig developed to demonstrate multi-contact dry-friction whip and whirl in the current work.

scholarly journals Students’ understanding level of friction force direction concept on rolling object

2019 ◽  
Vol 1153 ◽  
pp. 012150 ◽  
Author(s):  
C. Cari ◽  
Puspita Septim Wulandari ◽  
Nonoh Siti Aminah ◽  
Jeffry Handhika ◽  
Dewanta Arya Nugraha
Keyword(s):  
Friction Force ◽  
Force Direction

Forced Response Prediction of Blades With Loosely Assembled Dovetail Attachment by HBM

2009 ◽  
Author(s):  
Shangguan Bo ◽  
Zili Xu ◽  
Qilin Wu ◽  
XianDing Zhou ◽  
ShouHong Cao
Keyword(s):  
Friction Force ◽  
Centrifugal Force ◽  
Dry Friction ◽  
Harmonic Balance ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Balance Method ◽  
Force Model ◽  
Equivalent Stiffness ◽  
Equivalent Damping

To understand the mechanism of interfacial damping of axial loosely assembled dovetail to suppress blade vibration, a dry friction force model is presented by the Coulomb friction law and the macroslip model, and the mathematical expression of the friction force is derived. The nonlinear friction force is linearized as an equivalent stiffness and an equivalent damping through the one-term harmonic balance method. The effect of centrifugal force on the equivalent stiffness and the equivalent damping is studied. The forced response of one simplified blade with loosely assembled dovetail attachment is predicted by the harmonic balance method, in which the blade is described by the lumped mass and spring model, and the friction contact joints is simplified as a ideal friction damper. The results show that the equivalent stiffness of loosely assembled dovetail attachment increases with blade centrifugal force, gradually reaches a certain value, and there exists the maximum value for the equivalent stiffness. The equivalent damping increases at the beginning and then decreases with blade centrifugal force increasing, there exists a maximum too. The resonant frequency of blade rises with blade centrifugal force, but it no longer increases when the centrifugal force exceed a certain value. There exists a special centrifugal force on which the effect of dry friction damping is the best.

Investigation of Liquid Nitrogen Lubrication Effect in Cryogenic Machining

2005 ◽  
Author(s):  
Shane Y. Hong
Keyword(s):  
Low Temperature ◽  
Liquid Nitrogen ◽  
Friction Force ◽  
Low Carbon Steel ◽  
Hydrodynamic Effect ◽  
Test Results ◽  
Low Carbon ◽  
Cryogenic Machining ◽  
Carbide Insert ◽  
Lubrication Effect

In cryogenic machining, liquid nitrogen (LN2) is well recognized as an effective coolant due to its low temperature, however, its lubrication effect remains unknown. Our previous studies of the change in cutting forces, tool wear, chip microstructure, and friction coefficient indicate a possible lubrication effect by LN2. To verify proposed LN2 mechanisms and distinguish them, idealized disk-flat contact tests were performed. From the test results, the LN2 lubrication effect by altering material properties at low temperature was dependent on the material pairs. An uncoated carbide insert with a low carbon steel or titanium alloy disk test showed reduction of friction under LN2 cooling, but a coated insert increased the friction force. LN2 injection to form a physical barrier or hydrodynamic effect between two bodies is always effective to reduce friction force.

Review and comparison of dry friction force models

2015 ◽  
Vol 83 (4) ◽  
pp. 1785-1801 ◽  
Author(s):  
Ettore Pennestrì ◽  
Valerio Rossi ◽  
Pietro Salvini ◽  
Pier Paolo Valentini
Keyword(s):  
Friction Force ◽  
Dry Friction

Experimental Study on Multi-Mode Vibration Control of a Stay Cable with a Passive Magnetorheological Damper

2013 ◽  
Vol 361-363 ◽  
pp. 1402-1405
Author(s):  
Zhi Hao Wang
Keyword(s):  
Vibration Control ◽  
Mr Damper ◽  
Magnetorheological Damper ◽  
Test Results ◽  
Stay Cable ◽  
Mr Dampers ◽  
Stay Cables ◽  
Modal Damping ◽  
Mode Vibration ◽  
Multi Mode

Effective vibration control technology for stay cables is extremely critical to safe operations of cable-stayed bridges. For super-long cables, passive linear damper cannot provide sufficient damping since it can be only optimum for a given mode of cable, while a long cable may vibrate with several modes. This paper focuses on multi-mode vibration control of stay cables with passive magnetorheological (MR) dampers. Firstly, a 21.6m-long model cable was designed and established in the laboratory.Then, control performance of the cable with a passive MR damper was tested. The test results show that modal damping ratios of the cable in the first four modes can be improved significantly with the MR damper. It is further demonstrated that optimal tuned passively operated MR damper can outperform the passive viscous damper.

The Cutting Energy of Rubber Cutting by a Sharp Cutter

2007 ◽  
Vol 353-358 ◽  
pp. 3072-3075
Author(s):  
Ying Jin ◽  
Jian Hua Wu ◽  
Long Quan Liu ◽  
Zheng Qiang Yao
Keyword(s):  
Friction Force ◽  
Deformation Energy ◽  
Test Method ◽  
Test Results ◽  
Surface Fracture ◽  
Cutting Energy ◽  
Cutting Experiment ◽  
Punching Process ◽  
Different Thickness ◽  
Surface Fracture Energy

In order to obtain the total cutting energy and the ratios of the three parts of the total energy during cutting off the rubber, a test method was proposed and a test apparatus was constructed to perform the rubber cutting experiment. In the test, the friction force and the cutting force were obtained. Through the analysis of the test results, the friction work, the deformation energy, the surface fracture energy in cutting different thickness of the rubber were calculated. This work originally proposed a test method to acquire the friction force, the friction work between the cutter and workpiece during punching process.

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