In Situ Determination of Rolling Bearing Stiffness and Damping by Modal Analysis

1987 ◽  
Vol 109 (3) ◽  
pp. 235-240 ◽  
Author(s):  
J. Kraus ◽  
J. J. Blech ◽  
S. G. Braun
Keyword(s):  
Modal Analysis ◽  
Rolling Bearing ◽  
Operating Conditions ◽  
Rolling Bearings ◽  
Outer Race ◽  
Bearing Stiffness ◽  
Rotor Bearings ◽  
Stiffness And Damping

A method is presented for the extraction of rolling bearings characteristics (stiffness and damping) under operating conditions. The method is based on experimental modal analysis combined with a mathematical model of the rotor-bearings-support system. The method has been applied for the investigation of the effect of speed, preload, and free outer race bearings on system stiffness and damping. The method proves to be very accurate for stiffness determination and reasonably so for damping.

Traction Behavior of Some Lubricants Used for Rolling Bearings in Spacecraft Applications: Experiments and Thermal Model Based on Primary Laboratory Data

2001 ◽  
Vol 124 (1) ◽  
pp. 72-81 ◽  
Author(s):  
Daniel Ne´lias ◽  
Eric Legrand ◽  
Philippe Vergne ◽  
Jean-Bernard Mondier
Keyword(s):  
Thermal Model ◽  
Laboratory Data ◽  
Rolling Bearing ◽  
Operating Conditions ◽  
Model Parameters ◽  
Rolling Bearings ◽  
Traction Coefficient ◽  
Shear Heating ◽  
Rheological Experiments

Three synthetic oils used in spacecraft mechanisms (Pennzane SHF X2000, Nye 186 A, and Fomblin Z25) have been studied. Rheological tests were performed in order to characterize the behavior of each fluid versus pressure, temperature and shear rate. That includes the determination of the WLF viscosity model parameters. Tribological tests were carried out to measure the traction coefficient for operating conditions representative of spacecraft applications. Experimental results were compared with theoretical ones obtained using a non-newtonian thermal model. The modeling of traction in EHL contact is based on the Johnson and Tevaarwerk’s model modified to account for the shear heating of the fluid. The variations of the lubricant thermal conductivity with respect to temperature and pressure are also considered. In this model, input data comes directly from rheological experiments or are derived from other measurements through physical relationships. These rheological and tribological characterizations are essential to better describe the behavior of a lubricated rolling bearing.

scholarly journals Experimental Estimation of Journal Bearing Stiffness for Damage Detection in Large Hydrogenerators

2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Geraldo Carvalho Brito ◽  
Roberto Dalledone Machado ◽  
Anselmo Chaves Neto
Keyword(s):  
Damage Detection ◽  
Journal Bearing ◽  
Turbine Rotor ◽  
Journal Bearings ◽  
Operating Conditions ◽  
Tilting Pad ◽  
Theoretical Predictions ◽  
Bearing Stiffness ◽  
Stiffness And Damping

Based on experimental pieces of evidence collected in a set of twenty healthy large hydrogenerators, this article shows that the operating conditions of the tilting pad journal bearings of these machines may have unpredictable and significant changes. This behavior prevents the theoretical determination of bearing stiffness and damping coefficients with an adequate accuracy and makes damage detection difficult. Considering that dynamic coefficients have similar sensitivity to damage and considering that it is easier to monitor bearing stiffness than bearing damping, this article discusses a method to estimate experimentally the effective stiffness coefficients of hydrogenerators journal bearings, using only the usually monitored vibrations, with damage detection purposes. Validated using vibration signals synthesized by a simplified mathematical model that simulates the dynamic behavior of large hydrogenerators, the method was applied to a journal bearing of a 700 MW hydrogenerator, using two different excitations, the generator rotor unbalance and the vortices formed in the turbine rotor when this machine operates at partial loads. The experimental bearing stiffnesses obtained using both excitations were similar, but they were also much lower than the theoretical predictions. The article briefly discusses the causes of these discrepancies, the method’s uncertainties, and the possible improvements in its application.

Identification of Bearing Coefficients of Flexible Rotor-Bearing Systems

2000 ◽  
Author(s):  
Tachung Yang ◽  
Wei-Ching Chaung
Keyword(s):  
Industrial Applications ◽  
Operating Conditions ◽  
Least Square ◽  
Flexible Rotor ◽  
Fem Modeling ◽  
Identification Method ◽  
Reaction Forces ◽  
Manufacturing Assembly ◽  
Stiffness And Damping

The accuracy of stiffness and damping coefficients of bearings is critical for the rotordynamic analysis of rotating machinery. However, the influence of bearings depends on the design, manufacturing, assembly, and operating conditions of the bearings. Uncertainties occur quite often in manufacturing and assembly, which causes the inaccuracy of bearing predictions. An accurate and reliable in-situ identification method for the bearing coefficients is valuable to both analyses and industrial applications. The identification method developed in this research used the receptance matrices of flexible shafts from FEM modeling and the unbalance forces of trial masses to derive the displacements and reaction forces at bearing locations. Eight bearing coefficients are identified through a Total Least Square (TLS) procedure, which can handle noise effectively. A special feature of this method is that it can identify bearing coefficients at a specific operating speed, which make it suitable for the measurement of speed-dependent bearings, like hydrodynamic bearings. Numerical validation of this method is presented. The configurations of unbalance mass arrangements are discussed.

Experimental and Theoretical Rotordynamic Characteristics of a Hybrid Journal Bearing

1997 ◽  
Vol 119 (1) ◽  
pp. 132-141 ◽  
Author(s):  
J. T. Sawicki ◽  
R. J. Capaldi ◽  
M. L. Adams
Keyword(s):  
Journal Bearing ◽  
Operating Conditions ◽  
Dynamic Force ◽  
Test Results ◽  
Force Measurements ◽  
Lubrication Equation ◽  
Load Cells ◽  
Theoretical Predictions ◽  
Stiffness And Damping

This paper describes an experimental and theoretical investigation of a four-pocket, oil-fed, orifice-compensated hydrostatic bearing including the hybrid effects of journal rotation. The test apparatus incorporates a double-spool-shaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular orbit, for both forward and backward whirling. This configuration yields data that enables determination of the full linear anisotropic rotordynamic model. The dynamic force measurements were made simultaneously with two independent systems, one with piezoelectric load cells and the other with strain gage load cells. Theoretical predictions are made for the same configuration and operating conditions as the test matrix using a finite-difference solver of Reynolds lubrication equation. The computational results agree well with test results, theoretical predictions of stiffness and damping coefficients are typically within thirty percent of the experimental results.

Performance Analysis of Gas-Expanded Lubricants in a Hybrid Bearing Using Computational Fluid Dynamics

2015 ◽  
Author(s):  
Brian K. Weaver ◽  
Gen Fu ◽  
Andres F. Clarens ◽  
Alexandrina Untaroiu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Phase Behavior ◽  
Ambient Pressure ◽  
Operating Conditions ◽  
Full Potential ◽  
Dissolved Carbon ◽  
Bearing Stiffness ◽  
Multi Phase ◽  
Stiffness And Damping

Gas-expanded lubricants (GELs), tunable mixtures of synthetic oil and dissolved carbon dioxide, have been previously shown to potentially increase bearing efficiency, rotordynamic control, and long-term reliability in flooded journal bearings by controlling the properties of the lubricant in real time. Previous experimental work has established the properties of these mixtures and multiple numerical studies have predicted that GELs stand to increase the performance of flooded bearings by reducing bearing power losses and operating temperatures while also providing control over bearing stiffness and damping properties. However, to date all previous analytical studies have utilized Reynolds equation-based approaches while assuming a single-phase mixture under high-ambient pressure conditions. The potential implications of multi-phase behavior could be significant to bearing performance, therefore a more detailed study of alternative operating conditions that may include multi-phase behavior is necessary to better understanding the full potential of GELs and their effects on bearing performance. In this work, the performance of GELs in a fixed geometry journal bearing were evaluated to examine the effects of these lubricants on the fluid and bearing dynamics of the system under varying operating conditions. The bearing considered for this study was a hybrid hydrodynamic-hydrostatic bearing to allow for the study of various lubricant supply and operating conditions. A computational fluid dynamics (CFD)-based approach allowed for a detailed evaluation of the lubricant injection pathway, the flow of fluid throughout the bearing geometry, thermal behavior, and the collection of the lubricant as it exits the bearing. This also allowed for the study of the effects of the lubricant behavior on overall bearing performance.

scholarly journals On the Determination of Loop Nature in the Tem

1996 ◽  
Vol 439 ◽  
Author(s):  
M. L. Jenkins ◽  
H. Fukushima ◽  
M. A. Kirk
Keyword(s):  
Ion Irradiation ◽  
Large Fraction ◽  
Reciprocal Lattice ◽  
Direct Methods ◽  
Heavy Ion ◽  
Operating Conditions ◽  
Contrast Analysis ◽  
Small Clusters

AbstractWe have carried out systematic experiments to explore the range of applicability of the two direct methods which are available for the determination of the nature of small clusters. Experiments in heavy-ion irradiated silver and copper, including direct comparisons with the results of Black-White contrast analysis (B-W), forced us to the conclusion that use of the 21/2D technique for the analysis of faulted loops is effectively impossible because of reciprocal-lattice spike and other effects. We used B-W analysis to investigate the nature of the clusters produced by room-temperature heavy-ion irradiation of copper. In-situ irradiations were performed in the Argonne HVEM-Tandem Facility using 40keV and 80keV Kr+ ions. Nearly all of the analysable first-layer loops were found to be vacancy in nature. Some deeper clusters were also certainly vacancy. There is no unequivocal evidence for interstitial loops under these conditions. The near impossibility of establishing that interstitial loops are not present is shown by the fact that a large fraction of loops - over 50% - could not be analysed either because they did not display clear B-W contrast under any condition or sufficiently consistent B-W contrast under several different operating conditions.

Vibration Analysis of Statically Indeterminate Rotors With Hydrodynamic Bearings

1998 ◽  
Vol 120 (4) ◽  
pp. 781-788 ◽  
Author(s):  
N. S. Feng ◽  
E. J. Hahn
Keyword(s):  
Vibration Analysis ◽  
Operating Conditions ◽  
System Stability ◽  
Hydrodynamic Bearings ◽  
Hydrodynamic Bearing ◽  
Unbalance Response ◽  
Tilting Pad ◽  
The Stability ◽  
Rotor Bearings ◽  
Stiffness And Damping

In statically indeterminate rotor bearings systems, where the rotor is supported by one or more hydrodynamic bearings, the reactions at each hydrodynamic bearing, and hence its stiffness and damping properties depend not only on the bearing type, the operating conditions and the bearing dimensions but also on the relative lateral alignment between the journal and the bearing housing; the alignment, therefore, has a significant influence on the system stability and unbalance response. Additional complications arise if nonsymmetric bearing types such as elliptic or tilting pad bearings are present. An iterative procedure is outlined which enables the bearing reactions to be determined at any speed, thereby enabling even large systems such as turbomachinery to be rapidly analyzed in conjunction with existing linear rotor bearing vibration analysis software. Sample numerical examples show how misalignment and bearing type can affect the natural frequencies, the stability threshold, and the unbalance response of such statically indeterminate systems.

Transient Analysis of Gas-Expanded Lubrication and Rotordynamic Performance in a Centrifugal Compressor

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Brian K. Weaver ◽  
Jason A. Kaplan ◽  
Andres F. Clarens ◽  
Alexandrina Untaroiu
Keyword(s):  
Carbon Dioxide ◽  
High Speed ◽  
Operating Conditions ◽  
Damping Coefficients ◽  
Rotating Machine ◽  
Rapid Changes ◽  
Fluid Properties ◽  
Bearing Stiffness ◽  
Stiffness And Damping ◽  
Bearing Dynamics

Gas-expanded lubricants (GELs) have the potential to increase bearing energy efficiency, long-term reliability, and provide for a degree of control over the rotordynamics of high-speed rotating machines. Previous work has shown that these tunable mixtures of synthetic oil and dissolved carbon dioxide could be used to maximize the stability margin of a machine during startup by controlling bearing stiffness and damping. This allows the user to then modify the fluid properties after reaching a steady operating speed to minimize bearing power loss and reduce operating temperatures. However, it is unknown how a typical machine would respond to rapid changes in bearing stiffness and damping due to changes in the fluid properties once the machine has completed startup. In this work, the time-transient behavior of a high-speed compressor was evaluated numerically to examine the effects of rapidly changing bearing dynamics on rotordynamic performance. Two cases were evaluated for an eight-stage centrifugal compressor: an assessment under stable operating conditions as well as a study of the instability threshold. These case studies presented two contrasting sets of transient operating conditions to evaluate, the first being critical to the viability of using GELs in high-speed rotating machinery. The fluid transitions studied for machine performance were between that of a polyol ester (POE) synthetic lubricant and a GEL with a 20% carbon dioxide content. The performance simulations were carried out using a steady-state thermoelastohydrodynamic (TEHD) bearing model, which provided bearing stiffness and damping coefficients as inputs to a time-transient rotordynamic model using Timoshenko beam finite elements. The displacements and velocities of each node were solved for using a fourth-order Runge–Kutta method and provided information on the response of the rotating machine due to rapid changes in bearing stiffness and damping coefficients. These changes were assumed to be rapid due to (1) the short lubricant residence times calculated for the bearings and (2) rapid mixing due to high shear rates in the machine bearings causing sudden changes in the fluid properties. This operating condition was also considered to be a worst-case scenario as an abrupt change in the bearing dynamics would likely solicit a more extreme rotordynamic response than a more gradual change, making this analysis quite important. The results of this study provide critical insight into the nature of operating a rotating machine and controlling its behavior using GELs, which will be vital to the implementation of this technology.

A Multi-Fault Diagnosis Method of Rolling Bearing Based on Wavelet-PCA and Fuzzy K-Nearest Neighbor

2010 ◽  
Vol 29-32 ◽  
pp. 1602-1607 ◽  
Author(s):  
Xiang Shun Chen ◽  
Hu Biao Zeng ◽  
Zhi Xiong Li
Keyword(s):  
Fault Diagnosis ◽  
Nearest Neighbor ◽  
Rolling Bearing ◽  
Fault Detection And Diagnosis ◽  
Operating Conditions ◽  
K Nearest Neighbor ◽  
Rolling Bearings ◽  
Classification Rate ◽  
Wavelet Pca ◽  
Original Feature

Rolling bearings are widely used in various areas including aircraft, mining, manufacturing, and agriculture, etc. The breakdowns of the rotational machinery resulted from the rolling bearing failures account for 30%. It is therefore imperative to monitor the rolling bearing conditions in time in order to prevent the malfunctions of the plants. In the present paper is described a fault detection and diagnosis technique for rolling bearing multi-faults based on wavelet-principle component analysis (PCA) and fuzzy k-nearest neighbor (FKNN). In the diagnosis process, the wavelet analysis was firstly employed to decompose the vibration data of the rolling bearings under eight different operating conditions, and for each sample its energy of each sub-band was calculated to obtain the original feature space. Then, the PCA was used to reduce the dimensionality of the original feature vector and hence the most important features could be gotten. Lastly, the FKNN algorithm was employed in the pattern recognition to identify the conditions of the bearings of interest. The experimental results suggest that the sensitive fault features can be extracted efficiently after the wavelet-PCA processing, and the proposed diagnostic system is effective for the rolling bearing multi-fault diagnosis. In addition, the proposed method can achieve higher performance than that without PCA with respect to the classification rate.

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