In this paper, we present a review of the experimental identification of dynamic parameters of bearings in a rotating machine. Major emphasis is given to vibration-based identification methods and the review encompasses descriptions of experimental measurement techniques, mathematical modeling, parameter extraction algorithms and uncertainty in the estimates applied to a variety of bearings. The parameter extraction algorithms include the descriptions of governing equations of the rotor-bearing system and identification methods in both time and frequency domains. The identification techniques have been classified based on methods used to excite the system. The review includes a variety of bearings and similar components, which play an active link between the rotating and stationary parts of a machine. Based on the state of the art in bearing identification, conclusions are made and future directions are suggested.

Identification of Dynamic Bearing Parameters: A Review

Fluid film journal bearings (FFBs) are used to support high-speed rotors in turbomachinery which often operate above the rotor first bending critical speed. The FFBs provide both lateral support and dynamic coefficients: stiffness, damping, and mass terms, related to machine vibrations. Detailed numerical values of the bearing dynamic characteristics are necessary for proper design and operation of rotating machinery. The methods of the identification of fluid film journal bearing static and dynamic characteristics, particularly the bearing stiffness, damping, and mass coefficients, from measured data, obtained from different measurement systems, is reviewed. Many bearing tests have been performed to validate a number of different theoretical models, including the classical Reynolds isoviscous model. More advanced bearing models include the thermohydrodynamic (THD), and thermoelastohydrodynamic (TEHD) approaches. The advanced models also include turbulence effects which are important as rotor speeds continue to increase. The range of measured bearing data no longer includes current operational conditions. The various approaches to the bearing identification problem are discussed, including the different force excitation methods of incremental loading, sinusoidal, pseudorandom, impulse, known/additional unbalance, and non-contact excitation. Also bearing excitation and rotor excitation approaches are discussed. Data processing methods in the time and frequency domains are presented. Methods of evaluating the effects of measurement uncertainty on overall bearing coefficient confidence levels are reviewed. In this review, the relative strengths and weaknesses of bearing identification methods are presented, and developments and trends in improving bearing measurements are documented. Future trends in journal bearing identification improvement are discussed.

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Identification methods and test results for tilting pad and fixed geometry journal bearing dynamic coefficients – A review

The thermal analysis of flexure-pivot tilting-pad hybrid (combination hydrostatic-hydrodynamic) bearings for cryogenic turbopumps is presented. The advantages of this type of bearing for high speed operation are discussed. Turbulent bulk-flow, variable properties, momentum and energy transport equations of motion govern the flow in the bearing pads. Zeroth-order equations for the flow field at a journal equilibrium position render the bearing flow rate, load capacity, drag torque, and temperature rise. First-order equations for perturbed flow fields due to small amplitude journal motions provide rotordynamic force coefficients. A method to determine the tilting-pad moment coefficients from the force displacement coefficients is outlined. Numerical predictions correlate well with experimental measurements for tilting-pad hydrodynamic bearings. The design of a liquid oxygen, flexure-pad hybrid bearing shows a reduced whirl frequency ratio and without loss in load capacity or reduction in direct stiffness and damping coefficients.

Turbulent Flow, Flexure-Pivot Hybrid Bearings for Cryogenic Applications

Propeller induced structural vibration through the thrust bearing is an important source for low frequency shipboard noise and underwater sound radiation from a submarine hull. Such vibration is investigated using a scaled experimental model. This research concentrates on the experimental characterization of propeller force, hydrodynamic force of the thrust bearing and vibration transmission through a thrust bearing into the supporting structure. The results of laboratory measurement of the propeller force and the complex hydrodynamic stiffness of the thrust bearing are presented in this paper. The response of the shaft axial vibration and flexural vibration of the supporting structure is also analyzed.

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Propeller induced structural vibration through the thrust bearing

This paper presents measured results for the eccentricity ratios for two tilting-pad journal bearing. Comparison between a bearing with spherical seated ball and socket pad pivots and one with line contact rocker-back pad pivots is made. The bearings have a length to diameter ratio of 0.75, offset ratios of 0.50, preloads of about 0.320, a journal diameter of 70 mm and a radial machined pad clearance of 113.0 μm. Measurements were made for a range of speed-load conditions encompassing a Sommerfeld number range of 0.1 to 2.0. Comparison of the eccentricity magnitude for the two bearing agreed within uncertainty levels. For the bearing with rocker-back pad pivots, the journal attitude angle with respect to the applied load direction is nearly zero. Attitude angles range from 13° to 33° for the bearing with spherical seated ball and socket pad pivots. The deviation from zero attitude angle for this bearing increased with increasing speed. A hypothesis for larger pad pivot friction in the ball and socket pivo...

This paper presents measured and calculated characteristics of a tilting pad journal bearing suitable for high speed machinery. Descriptions are given of the experimental techniques used with this variety of bearing and the theoretical model for predicting performance. Measured values of pad temperature, eccentricity, attitude angle, and the four stiffness coefficients are given for a range of loads and rotational speeds. Data are given for both load on pad and between pad configurations, the two principal loading arrangements. Comparisons are made between the measured and predicted bearing temperatures and stiffness coefficients over a wide range of values. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Diego, California, October 19–21, 1992

D. Horner

Papers

Tilting Pad Journal Bearings — Measured and Predicted Stiffness Coefficients