Articles de revues sur le sujet « Rotor dynamics, Tilting Pad Journal Bearing, Turbomachinery »
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1
Dimond, T. W., P. N. Sheth, P. E. Allaire et M. He. « Identification Methods and Test Results for Tilting Pad and Fixed Geometry Journal Bearing Dynamic Coefficients – A Review ». Shock and Vibration 16, no 1 (2009) : 13–43. http://dx.doi.org/10.1155/2009/708363.
Texte intégralRésumé :
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.
2
Ciulli, Enrico, Paola Forte, Flavio Antonelli, Roberto Minelli et Daniele Panara. « Tilting Pad Journal Bearing Ball and Socket Pivots : Experimental Determination of Stiffness ». Machines 10, no 2 (23 janvier 2022) : 81. http://dx.doi.org/10.3390/machines10020081.
Texte intégralRésumé :
Tilting pad journal bearings (TPJB) are used in turbomachinery for their stability at high speeds. For design purposes, it is necessary to preliminarily investigate the turbomachine rotor dynamic behavior by simulation. The dynamic characteristics of all components must be known as precisely as possible and experimental validation of each single model is required. While a lot of work has been carried out on bearings, the ball-and-socket stiffness is still estimated by means of Hertzian formulas. Recently, some authors have used the finite element method, but it seems that nothing has been done experimentally to date. This paper describes the test rig designed to determine the stiffness of a TPJB ball-and-socket pivot by equipping the grippers of a tensile universal testing machine with specifically designed interfaces. A methodology for evaluating the stiffness from the experimental results is reported. Preliminary compression results are presented and compared with the analytical ones obtained using Hertz’s formula showing significant differences for the ball-and-socket conformal contact.
3
Chan, D. S. H. « Nonlinear Analysis of Rotordynamic Instabilities in High-Speed Turbomachinery ». Journal of Engineering for Gas Turbines and Power 118, no 1 (1 janvier 1996) : 122–29. http://dx.doi.org/10.1115/1.2816527.
Texte intégralRésumé :
A nonlinear approach based on the method of averaging has been developed to study unstable lateral vibrations of rotors in high-speed turbomachinery. The method makes use of an extended concept of bearing dynamic coefficients, which are defined by applying small perturbations to the dynamic equilibrium positions. The approach has been applied to determine the stability threshold of flexible rotors supported on short and tilting-pad journal bearings, respectively. Stability performance of systems supported on short journal bearings is improved by the presence of mass unbalance. However, for flexible rotors supported on tilting-pad journal bearings, increased unbalance can lead to lower rotordynamic stability margins. This has the significant implication that stability estimates from linear analysis are not always conservative. The present method provides a computationally more efficient way to understand the nonlinear vibration behavior of high-speed turbomachinery.
4
Ying, Jiayang, Yinghou Jiao et Zhaobo Chen. « Nonlinear Dynamics Analysis of Tilting Pad Journal Bearing-Rotor System ». Shock and Vibration 18, no 1-2 (2011) : 45–52. http://dx.doi.org/10.1155/2011/213742.
Texte intégralRésumé :
The nonlinear dynamics theory is increasingly applied in the dynamics analysis of tilting pad journal bearing-rotor system. However, extensive work on system dynamics done previously neglects the influence caused by the moment of inertia of the pad. In this paper, a comparison is made between the responses of the rotor in the bearings with and without pad inertia effect. Taking the Jeffcott rotor system as an example, the characteristics of bearing-rotor system, such as bifurcation diagram, cycle response, frequency spectrum, phase trajectories, and Poincaré maps, were attained within a certain rotation rate range. The pivotal oil-film force of tilting pad journal bearing was calculated by database method. The results directly demonstrate that considering the influence of the pad moment of inertia, system dynamics characteristics are found more complicated when rotor-bearing system works around natural frequency and system bifurcation is observed forward when rotor-bearing system works on high-speed range.
5
Kirk, R. G., et S. W. Reedy. « Evaluation of Pivot Stiffness for Typical Tilting-Pad Journal Bearing Designs ». Journal of Vibration and Acoustics 110, no 2 (1 avril 1988) : 165–71. http://dx.doi.org/10.1115/1.3269494.
Texte intégralRésumé :
The manufacturers of high speed turbomachinery are concerned with the accurate prediction of rotor response and stability. One major factor in the placement of system critical speeds and amplification factors is the stiffness and damping of both the fluid-film bearing and support structure. Typical calculated results for tilting-pad fluid-film bearings have neglected the influence of the point or line contact of the pivot support for the individual pads. This paper will review the equations developed considering the Hertzian contact stress and deformation theory and present the equations for pivot stiffness necessary for inclusion in tilting pad bearing computer programs. In addition, the influence of various standard pivot designs will be compared for typical fluid-film bearing stiffness and damping characteristics.
6
Brancati, Renato, Stefano Pagano, Ernesto Rocca, Michele Russo et Riccardo Russo. « Experimental Investigations on Tilting Pad Journal Bearings ». International Journal of Rotating Machinery 5, no 3 (1999) : 181–91. http://dx.doi.org/10.1155/s1023621x99000160.
Texte intégralRésumé :
The results of a survey conducted on an experimental system consisting of a rigid rotor supported on two radial bearings each with five tilting pads is presented. In particular, the system was set up in order to assess the dynamic behaviour of the bearing in unusual operating conditions. The response of the bearing to different unbalance values was determined after acquiring and analysing the orbits described by the journal axis for assigned unbalance values in different operating conditions. Analysis of the results shows some particular operating features that were not entirely predicted by the theoretical model and which may give rise to malfunctions in the rotor-tilting pad bearings system. The tests were carried out in the rotor dynamics laboratory of the Dipartimento di Ingegneria Meccanica per l'Energetica at the University of Naples.
7
Vázquez, J. A., et L. E. Barrett. « Modeling of Tilting-Pad Journal Bearings with Transfer Functions ». International Journal of Rotating Machinery 7, no 1 (2001) : 1–10. http://dx.doi.org/10.1155/s1023621x0100001x.
Texte intégralRésumé :
Tilting-pad journal bearings are widely used to promote stability in modern rotating machinery. However, the dynamics associated with pad motion alters this stabilizing capacity depending on the operating speed of the machine and the bearing geometric parameters, particularly the bearing preload. In modeling the dynamics of the entire rotor-bearing system, the rotor is augmented with a model of the bearings. This model may explicitly include the pad degrees of freedom or may implicitly include them by using dynamic matrix reduction methods. The dynamic reduction models may be represented as a set of polynomials in the eigenvalues of the system used to determine stability. All tilting-pad bearings can then be represented by a fixed size matrix with polynomial elements interacting with the rotor. This paper presents a procedure to calculate the coefficients of polynomials for implicit bearing models. The order of the polynomials changes to reflect the number of pads in the bearings. This results in a very compact and computationally efficient method for fully including the dynamics of tilting-pad bearings or other multiple degrees of freedom components that interact with rotors. The fixed size of the dynamic reduction matrices permits the method to be easily incorporated into rotor dynamic stability codes. A recursive algorithm is developed and presented for calculating the coefficients of the polynomials. The method is applied to stability calculations for a model of a typical industrial compressor.
8
Feng, N. S., et E. J. Hahn. « Vibration Analysis of Statically Indeterminate Rotors With Hydrodynamic Bearings ». Journal of Tribology 120, no 4 (1 octobre 1998) : 781–88. http://dx.doi.org/10.1115/1.2833779.
Texte intégralRésumé :
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.
9
Ma, Hui, Zhao Hui Ren, Ji Shuang Dai et Bang Chun Wen. « Research on Dynamics of Rotor Systems in Large Centrifugal Compressor ». Key Engineering Materials 419-420 (octobre 2009) : 121–24. http://dx.doi.org/10.4028/www.scientific.net/kem.419-420.121.
Texte intégralRésumé :
It is important to study system vibration characteristics for improving product quality and ensuring safety operation of units. In this paper, some dynamics of rotor systems are studied in large centrifugal compressor. The models of diaphragm coupling and tilting pad bearing are established by appropriate simplification. The finite element model of rotors with bearing and coupling is set up by taking interrelation of these subsystems into account. The unbalance responses of journal are computed based on the relative standard. The effect of bearing parameters (length-diameter ratio, clearance ratio and lubricating oil number) to journal vibration of rotor systems is analyzed. Finally test results and theoretical results are compared and errors are analyzed. The research results will provide theoretical basis for improving the bearing design of compressor rotor systems.
10
Abu-Mahfouz, Issam, et Maurice L. Adams. « Numerical Study of Some Nonlinear Dynamics of a Rotor Supported on a Three-Pad Tilting Pad Journal Bearing (TPJB) ». Journal of Vibration and Acoustics 127, no 3 (1 juin 2005) : 262–72. http://dx.doi.org/10.1115/1.1888593.
Texte intégralRésumé :
The use of tilting pad journal bearings (TPJBs) has increased in the recent past due to their stabilizing effects on the rotor bearing system. However, in this paper two mechanisms capable of producing instabilities in terms of subharmonic and chaotic motions are suggested. The first one is that of a centrally loaded pad with rotor unbalance excitations. The second one represents a concentric rotor (or a vertical rotor) acted upon by centering sprigs and large unbalance excitations. Extensive numerical experimentation shows, for certain parameters, subharmonic, quasi-periodic, and chaotic motions. The pad state space trajectory, in many cases, resembles that of the two-well potential case as in Duffing’s oscillator. Time trajectories, Poincare maps, fast Fourier transform (FFT) plots, and the max Lyapunov exponent are utilized to examine the periodicity (order) of the nonsynchronous rotor orbits and pad trajectories. The TPJB problem belongs to a family of nonlinear rotor-dynamical phenomena that are potentially of a considerable value as diagnostic tools in assessing rotating machinery condition monitoring.
11
Lü, Yan-jun, Yong-fang Zhang, Yang-bing Yu et Lie Yu. « Nonlinear dynamics of flexible rotor system supported on fixed-tilting pad combination journal bearing ». Journal of Central South University 18, no 3 (juin 2011) : 610–17. http://dx.doi.org/10.1007/s11771-011-0738-y.
Texte intégral
12
Teo, C. J., et Z. S. Spakovszky. « Analysis of Tilting Effects and Geometric Nonuniformities in Micro-hydrostatic Gas Thrust Bearings ». Journal of Turbomachinery 128, no 4 (1 février 2005) : 606–15. http://dx.doi.org/10.1115/1.2219761.
Texte intégralRésumé :
The Massachusetts Institute of Technology (MIT) microengine rotors are supported by hydrostatic gas journal and hydrostatic gas thrust bearings. Due to the low length-to-diameter ratio of the devices, the thrust bearings play an important role in providing sufficient tilting stiffness to resist any tilting motion about the spinning axis of the rotor. The performance of the thrust bearings can be influenced by geometric nonuniformities such as thrust-bearing clearances and orifice diameters, and profiles which arise in the process of micro-fabrication. To enable stable high speed operation of the micro-devices, it is important to quantify these effects. Furthermore, a thrust-bearing analysis tool needs to be developed that is able to explore different thrust-bearing arrangements and configurations. In this work, an analytical model is established for analyzing the effects of rotor tilt and geometric nonuniformities in micro-hydrostatic gas thrust bearings for application to micro-turbomachinery. A previously developed model (Teo and Spakovszky, 2006, “Modeling and Experimental Investigation of Micro-hydrostatic Gas Thrust Bearings for Micro-turbomachines,” ASME J. Turbomach., 128, pp. 597–605) is generalized and extended for application to thrust bearings with orifices arranged in nonaxisymmetric configurations. As a consequence of rotor tilt or geometric nonuniformities, the flow through individual orifices of the thrust bearing becomes nonuniform. The orifice flows are in turn coupled to the hydrostatic pressure field in the thrust-bearing pad, and a Green’s function approach is adopted to solve the coupled system. The hydrodynamic thrust-bearing forces induced by the pumping action of the rotor rotation are determined by solving the Reynolds equation. The model is able to predict thrust-bearing tilting stiffness and variations in the thrust-bearing mass flow rates as a function of rotor tilting angle for a variety of orifice arrangements. The model can be applied to analyze the effects of nonuniformities in orifice diameter and the presence of clogged orifices on tilting and the concomitant reduction in tilting stiffness. In addition, the effects of orifice taper are analyzed using an influence-coefficient method for one-dimensional compressible, viscous flows. Results obtained for various taper ratios are presented and discussed. The model serves as a useful tool for specifying design tolerances during the fabrication of micro-hydrostatic gas thrust bearings and is used in the experiments to estimate the tilting angle of the rotor during operation.
13
Benti, Gudeta Berhanu, Rolf Gustavsson et Jan-Olov Aidanpää. « Speed-Dependent Bearing Models for Dynamic Simulations of Vertical Rotors ». Machines 10, no 7 (10 juillet 2022) : 556. http://dx.doi.org/10.3390/machines10070556.
Texte intégralRésumé :
Many dynamic simulations of a rotor with a journal bearing employ non-linear fluid-film lubrication models and calculate the bearing coefficients at each time step. However, calculating such a simulation is tedious and computationally expensive. This paper presents a simplified dynamic simulation model of a vertical rotor with tilting pad journal bearings under constant and variable (transient) rotor spin speed. The dynamics of a four-shoes tilting pad journal bearing are predefined using polynomial equations prior to the unbalance response simulations of the rotor-bearing system. The Navier–Stokes lubrication model is solved numerically, with the bearing coefficients calculated for six different rotor speeds and nine different eccentricity amplitudes. Using a MATLAB inbuilt function (poly53), the stiffness and damping coefficients are fitted by a two-dimensional polynomial regression and the model is qualitatively evaluated for goodness-of-fit. The percentage relative error (RMSE%) is less than 10%, and the adjusted R-square (Radj2) is greater than 0.99. Prior to the unbalance response simulations, the bearing parameters are defined as a function of rotor speed and journal location. The simulation models are validated with an experiment based on the displacements of the rotor and the forces acting on the bearings. Similar patterns have been observed for both simulated and measured orbits and forces. The resultant response amplitudes increase with the rotor speed and unbalanced magnitude. Both simulation and experimental results follow a similar trend, and the amplitudes agree with slight deviations. The frequency content of the responses from the simulations is similar to those from the experiments. Amplitude peaks, which are associated with the unbalance force (1 × Ω) and the number of pads (3 × Ω and 5 × Ω), appeared in the responses from both simulations and experiments. Furthermore, the suggested simulation model is found to be at least three times faster than a classical simulation procedure that used FEM to solve the Reynolds equation at each time step.
14
da Silva, Danilo Alvaro, Gregory Bregion Daniel et Katia Lucchesi Cavalca. « Development of a Robust Test Rig for Tilting Pad Journal Bearing Validation ». Machines 10, no 3 (5 mars 2022) : 189. http://dx.doi.org/10.3390/machines10030189.
Texte intégralRésumé :
Several theoretical models for predicting the performance of tilting pad journal bearings (TPJB) have been developed by the scientific community over the years. However, reliable validation of the predictions based on the theoretical models, taking into account the complexity of TPJBs, demands robustness in the design and assembly of an improved test rig. Test bench designs for testing hydrodynamic bearings must carefully consider construction details as much as possible to observe the effect from the journal bearing and, consequently, improve the predictability of its dynamical behavior. In this context, there are still relatively few test rigs in the specific literature devoted to isolating the dynamic effects from hydrodynamic bearings for analysis purposes. Therefore, a novel test rig project is described in this work, also involving the design versatility characterized by measurement feasibility in rolling-element bearings and fixed-geometry, hydrodynamic journal bearings. This test rig aims to reproduce the most diverse operating conditions in order to measure the involved physical responses and validate the different models applied to the bearings. Therefore, the bearing performance can be properly evaluated, especially when operating under critical operating conditions, thus providing important contributions to the area of lubrication and rotor dynamics.
15
Parovay, E. F. « Influence of pad geometry and method of oil supply on the thermal state of GTE rotor tilting-pad journal bearing ». VESTNIK of Samara University. Aerospace and Mechanical Engineering 21, no 2 (7 juillet 2022) : 80–92. http://dx.doi.org/10.18287/2541-7533-2022-21-2-80-92.
Texte intégralRésumé :
High heat generation in the hydrodynamic wedge is one of the main factors limiting application of pad journal bearings as bearings for rotors of aircraft gas turbine engines. The goal of the research is to study the influence of the oil supply method on the bearing thermal state and to determine the design factors reducing the bearing temperature. The study was carried out with the use of bearings with diameters of 100320 mm with different design of the oil supply: through oil dispensing grooves in the pads, through oil nozzles in the inter-pad space, using lead-in chamfers for the pads, with oil bypass channels. The tasks posed were solved by using volumetric geometric models with the tools of computational fluid dynamics in the ANSYS CFX package in which differential equations describing the model are solved by the finite element method. The patterns of temperature and pressure distribution over the surface of the lower, most loaded bearing pad were obtained for various options of oil supply and different geometry of bearing pads; values of the bearing load carrying capacity, maximum pressure in the working gap, the oil mass flow through the elements of the oil supply; dependences of the bearing static performance on the distance between the shaft and nozzles. Oil supply through oil dispensing grooves made in pads is a factor that negatively affects the bearing thermal state, which is associated with so-called locking of the working gap. It is shown that implementation of oil supply through the space between the pads is more efficient. The use of a lead-in chamfer with plain inserts simplifies oil supply to the working gap. The design solutions described make it possible to reduce the maximum oil temperature in the bearing by 36 degrees Celsius.
16
Mehdi, Syed Muntazir, et Tae Ho Kim. « Computational Model Development for Hybrid Tilting Pad Journal Bearings Lubricated with Supercritical Carbon Dioxide ». Applied Sciences 12, no 3 (26 janvier 2022) : 1320. http://dx.doi.org/10.3390/app12031320.
Texte intégralRésumé :
Fluid film bearings lubricated with supercritical carbon dioxide (sCO2) eliminate the infrastructural requirement for oil lubricant supply and sealing in turbomachinery for sCO2 power systems. However, sCO2’s thermohydrodynamic properties, which depend on pressure and temperature, pose a challenge, particularly with computational model development for such bearings. This study develops a computational model for analyzing sCO2-lubricated tilting pad journal bearings (TPJBs) with external pressurization. Treating sCO2 as a real gas, the Reynolds equation for compressible turbulent flows solves the pressure distribution using the finite element method, and the Newton−Raphson method determines the static equilibrium position by simultaneously calculating forces, moments, flow rates of externally pressurized sCO2, and pressure drop due to flow inertia. The finite difference method solves the energy equation for temperature distribution. The density and viscosity of sCO2 are converged using the successive substitution method. The obtained predictions agree with the previous and authors’ computational fluid dynamics predictions, thus validating the developed model. Hybrid lubrication increases the minimum film thickness and stiffness up to 80% and 65%, respectively, and decreases the eccentricity ratio by up to 65% compared to those of pure hydrodynamic TPJB, indicating significant improvement in the load capacity. The bearing performance is further improved with increasing sCO2 supply pressure.
17
Ferfecki, Petr, Jaroslav Zapoměl, Marek Gebauer, Václav Polreich et Jiří Křenek. « A computational fluid dynamics investigation of the segmented integral squeeze film damper ». MATEC Web of Conferences 254 (2019) : 08005. http://dx.doi.org/10.1051/matecconf/201925408005.
Texte intégralRésumé :
Rotor vibration attenuation is achieved with damping devices which work on different, often mutually coupled, physical principles. Squeeze film dampers are damping devices that have been widely used in rotordynamic applications. A new concept of a 5-segmented integral squeeze film damper, in which a flexure pivot tilting pad journal bearing is integrated, was investigated. The damper is studied for the eccentric position between the outer and inner ring of the squeeze film land. The ANSYS CFX software was used for solving the pressure and velocity distribution. The development of the complex three-dimensional computational fluid dynamics model of the squeeze film damper, learning more about the effect of the forces in the damper, and the knowledge about the behaviour of the flow are the principal contributions of this article.
18
Santos, I. F., et A. Scalabrin. « Control System Design for Active Lubrication With Theoretical and Experimental Examples ». Journal of Engineering for Gas Turbines and Power 125, no 1 (27 décembre 2002) : 75–80. http://dx.doi.org/10.1115/1.1451757.
Texte intégralRésumé :
This work focuses on the theoretical and experimental behavior of rigid rotors controlled by tilting-pad journal bearings with active oil injection. Initially the mathematical model of the active bearing is presented: The equations that describe the dynamics of hydraulic actuators are introduced into the equations of the lubricant, resulting in a new form of Reynolds’ equation for active lubrication. The global model of the system is obtained by coupling the equation of motion of the rigid rotor with the stiffness and damping of the active oil film. This global model is then used to design the control system of the active bearing based on root locus curves. The active system stability is analyzed by calculating its eigenvalues and frequency response curves. The theoretical and experimental results show that this kind of bearing can significantly reduce the vibration level of rotating machinery.
19
Li, Mengxuan, Chaohua Gu, Xiaohong Pan, Shuiying Zheng et Qiang Li. « A new dynamic mesh algorithm for studying the 3D transient flow field of tilting pad journal bearings ». Proceedings of the Institution of Mechanical Engineers, Part J : Journal of Engineering Tribology 230, no 12 (5 août 2016) : 1470–82. http://dx.doi.org/10.1177/1350650116638610.
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A new dynamic mesh algorithm is developed in this paper to realize the three-dimensional (3D) computational fluid dynamics (CFD) method for studying the small clearance transient flow field of tilting pad journal bearings (TPJBs). It is based on a structured grid, ensuring that the total number and the topology relationship of the grid nodes remain unchanged during the dynamic mesh updating process. The displacements of the grid nodes can be precisely recalculated at every time step. The updated mesh maintains high quality and is suitable for transient calculation of large journal displacement in FLUENT. The calculation results, such as the static equilibrium position and the dynamic characteristic coefficients, are consistent with the two-dimensional (2D) solution of the Reynolds equation. Furthermore, in the process of transient analysis, under conditions in which the journal is away from the static equilibrium position, evident differences appear between linearized and transient oil film forces, indicating that the nonlinear transient calculation is more suitable for studying the rotor-bearing system.
20
Zemella, Philipp, Thomas Hagemann, Bastian Pfau et Hubert Schwarze. « Identification of Dynamic Coefficients of a Five-Pad Tilting Pad Journal Bearing Up to Highest Surface Speeds ». Journal of Engineering for Gas Turbines and Power 143, no 8 (31 mars 2021). http://dx.doi.org/10.1115/1.4049664.
Texte intégralRésumé :
Abstract Tilting-pad journal bearings are widely used in turbomachinery industry due to their positive dynamic properties at high rotor speeds. However, the exact description of this dynamic behavior is still part of current research. This paper presents the measurement results for a five-pad tilting-pad journal bearing in load between pivot configurations. The bearing is characterized by a nominal diameter of 100 mm, a length of 90 mm, and a pivot offset of 0.6. Investigations include the results for surface speeds between 25 and 120 m/s and specific bearing loads ranging from 0.0 to 3.0 MPa. The results of theoretical predictions are commonly derived from perturbation of stationary operation under static load. Therefore, experimental results for stationary operation including pad deflection under static load are presented first to characterize the investigated bearing. Measured results indicate considerable nonlaminar flow in the upper region of the investigated range of rotor speeds. Second, dynamic excitation tests are performed with excitation frequencies up to 400 Hz to evaluate dynamic coefficients of a stiffness (K) and damping (C) KC model, and additionally, a KCM model using additional virtual mass (M) coefficients. KCM coefficients are obtained by fitting frequency dependent KC-characteristics to the KCM model structure using least square approach. The wide range of rotating and excitation frequencies leads to subsynchronous as well as supersynchronous vibrations. Excitation forces are applied with multisinus and single-sinus characteristics. The latter one allows evaluation of KC coefficients at the particular frequency ratio in the time domain. Here, frequency and time domain evaluation algorithms for dynamic coefficients are used in order to assess their special properties and quality. The impact of surface speed, bearing load, and oil flow rate on measured and predicted KCM coefficients is investigated. Measured and predicted results can be well fitted to a KCM model and show a significant influence of the ratio between fluid film and pivot support stiffness on the speed dependent characteristic of bearing stiffness coefficients. However, the impact of this ratio on damping coefficients is considerably lower. Further investigations on the impact of oil flow rates indicate that a significant decrease of direct damping coefficients exists below a certain level of starvation. Above this limit, direct damping coefficients are nearly independent of oil flow rate. Results are analyzed in detail and demands on improvements for predictions are derived.
21
Weaver, Brian K., Ya Zhang, Andres F. Clarens et Alexandrina Untaroiu. « Nonlinear Analysis of Rub Impact in a Three-Disk Rotor and Correction Via Bearing and Lubricant Adjustment ». Journal of Engineering for Gas Turbines and Power 137, no 9 (1 septembre 2015). http://dx.doi.org/10.1115/1.4029778.
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Rubbing between rotating and stationary surfaces in turbomachinery can result in catastrophic failures if not caught quickly. Removing the rub impact can then often require time consuming and expensive solutions including field balancing or magnetic bearing systems. However, simple changes in bearing dynamics via bearing and lubricant adjustment could provide for a faster and cheaper alternative. In this work, a three-disk rotor was examined analytically for nonlinear rotordynamic behavior due to an unbalance-driven rub. The rotordynamic solution was obtained using nonlinear and steady state finite element models to demonstrate the effect of the rub impact on the dynamic response of the machine. A thermoelastohydrodynamic (TEHD) model of tilting pad journal bearing performance was also used to study the possible removal of the rub impact by making minor adjustments to bearing parameters including preload, clearance, pad orientation, and lubricant properties. Gas-expanded lubricants (GELs), tunable mixtures of synthetic oil and carbon dioxide that have been proposed as a means to provide control in bearing-rotor systems, were also considered for their possible role in controlling the rub. The TEHD model provided a range of bearing inputs to the rotor models in the form of stiffness and damping coefficients. Results from the rotordynamic analyses included an assessment of critical speeds, peak rotor displacements, and vibration characteristics. Individual bearing parameter adjustments were found to have smaller, though still significant effects on the response of the machine. Overall, it was found that by adjusting a combination of these bearing parameters, the peak displacement of the rotor could be reduced by large enough amounts to remove the rub impact in the machine, hence providing a simple approach to solving rub impact problems in rotating machinery caused by excessive vibration.
22
Griffini, Duccio, Simone Salvadori, Enrico Meli, Simone Panconi, Alessandro Ridolfi, Andrea Rindi, Francesco Martelli, Daniele Panara et Leonardo Baldassarre. « An Efficient Iterative Coupled Model for the Study of the Insurgence of the Morton Effect in Tilting Pad Journal Bearings ». Journal of Engineering for Gas Turbines and Power 141, no 5 (19 décembre 2018). http://dx.doi.org/10.1115/1.4041107.
Texte intégralRésumé :
The introduction of the tilting pad journal bearing (TPJB) technology has allowed the achievement of important goals regarding turbomachinery efficiency in terms of high peripheral speed, enhanced power density, higher efficiency, and tolerated loads. That kind of technology overcomes the typical dynamic instability problem that affects fixed geometry bearings but, under certain working conditions, can be subjected to thermal instability phenomena, which are particularly significant at high peripheral speeds. In this work, the authors propose an innovative iterative procedure to forecast the thermal instability onset by using two coupled models, a thermo-structural one and a fluid dynamic one. The first one calculates the vibrations and the deformations due both to the external forces and to the temperature distribution applied on the rotor. The fluid dynamic model calculates the temperature profile by using as inputs the characteristics of the rotor, of the bearing and of the orbits, obtained by the thermos-structural code. After a general description of the iterative procedure is given, details of each tool are provided. Code validation is presented by means of comparison with available experimental and numerical data. Finally, the results of the iterative procedure are shown to prove its potential in forecasting instability thresholds. The model has shown a good trade-off between accuracy and efficiency, which is very critical when dealing with the extended time windows characterizing thermal instabilities. This research activity is in cooperation with the industrial partner Baker Hughes, a GE company, which provided the experimental data obtained thorough a dedicated experimental campaign.
23
Mermertas, Ümit, Thomas Hagemann et Clément Brichart. « Optimization of a 900 mm Tilting-Pad Journal Bearing in Large Steam Turbines by Advanced Modeling and Validation ». Journal of Engineering for Gas Turbines and Power 141, no 2 (29 octobre 2018). http://dx.doi.org/10.1115/1.4041116.
Texte intégralRésumé :
Modernization of steam turbine components can extend power plant lifetime, decrease maintenance costs, increase service intervals, and improve operational flexibility. However, this can also lead to challenging demands for existing components such as bearings, e.g., due to increased rotor weights. Therefore, a careful design and evaluation process of bearings is of major importance. This paper describes the applied advanced modeling methods and performed validation for the optimization of a novel 900 mm three-pad tilting pad journal bearing that showed high temperature sensitivity to the fresh oil supply temperature. The bearing was developed to cope with increased rotor weights within the low pressure (LP) steam turbine modernization at two 1000 MW nuclear power plants. With a static load of 2.7 MN at a speed of 1500 rpm, it represents one of the highest loaded applications for tilting pad bearings in turbomachinery worldwide. After identification of the reasons for the sensitivity, advanced modeling methods were applied to optimize the bearing. For this purpose, a more comprehensive bearing model was developed considering the direct lubrication at the leading pad edge and pad deformation. The results of the entire analyses indicated modifications of bearing clearances, pad length, thickness, and pivot position. The optimized bearing was then implemented on both units and proved its excellent operational behavior at increased fresh oil supply temperatures of up to 55 °C. In conclusion, the application of advanced modeling methods proved to be the key success factor in the optimization of this bearing, which represents an optimal solution for turbomachinery.
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Andrés, Luis San, et Yingkun Li. « Effect of Pad Flexibility on the Performance of Tilting Pad Journal Bearings—Benchmarking a Predictive Model ». Journal of Engineering for Gas Turbines and Power 137, no 12 (16 septembre 2015). http://dx.doi.org/10.1115/1.4031344.
Texte intégralRésumé :
Tilting pad journal bearings (TPJBs) supporting high-performance turbomachinery rotors have undergone steady design improvements to satisfy ever stringent operating conditions that include large specific loads, due to smaller footprints, and high surface speeds that promote flow turbulence and hence larger drag power losses. Simultaneously, predictive models continuously evolve to include minute details on bearing geometry, pads and pivots' configurations, oil delivery systems, etc. In general, predicted TPJB rotordynamic force coefficients correlate well with experimental data for operation with small to moderately large unit loads (1.7 MPa). Experiments also demonstrate bearing dynamic stiffnesses are frequency dependent, best fitted with a stiffness-mass like model whereas damping coefficients are adequately represented as of viscous type. However, for operation with large specific loads (>1.7 MPa), poor correlation of predictions to measured force coefficients is common. Recently, an experimental effort (Gaines, J., 2014, “Examining the Impact of Pad Flexibility on the Rotordynamic Coefficients of Rocker-Pivot-Pad Tiling-Pad Journal Bearings,” M.S. thesis, Mechanical Engineering, Texas A&M University, College Station, TX) produced test data for three TPJB sets, each having three pads of unequal thickness, to quantify the effect of pad flexibility on the bearings' force coefficients, in particular damping, over a range of load and rotational speed conditions. This paper introduces a fluid film flow model accounting for both pivot and pad flexibility to predict the bearing journal eccentricity, drag power loss, lubricant temperature rise, and force coefficients of typical TPJBs. A finite element (FE) pad structural model including the Babbitt layer is coupled to the thin film flow model to determine the mechanical deformation of the pad surface. Predictions correlate favorably with test data, also demonstrating that pad flexibility produces a reduction of up to 34% in damping for the bearing with the thinnest pads relative to that with the thickest pads. A parametric study follows to quantify the influence of pad thickness on the rotordynamic force coefficients of a sample TPJB with three pads of increasing preload, r¯p = 0, 0.25 (baseline) and 0.5. The bearing pads are either rigid or flexible by varying their thickness. For design considerations, dimensionless static and dynamic characteristics of the bearings are presented versus the Sommerfeld number (S). Pad flexibility shows a more pronounced effect on the journal eccentricity and the force coefficients of a TPJB with null pad preload than for the bearings with larger pad preloads (0.25 and 0.5), in particular for operation with a small load or at a high surface speed (S > 0.8).
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Li, Ming, Xingxing Liu, Rui Zhu, Xiaohu Wang, Huiyu Bai, Fucai Li, Hongguang Li et Guang Meng. « Rotor Dynamics Behavior of Tilting Pad Bearing Supported Turbo-Expander Considering Temperature Gradient ». Journal of Computational and Nonlinear Dynamics 11, no 2 (26 août 2015). http://dx.doi.org/10.1115/1.4030831.
Texte intégralRésumé :
This paper dedicates on the rotor dynamics behavior analysis on a tilting pad bearing supported turbo-expander rotor system considering temperature gradient. Both numerical and experimental investigations are conducted intensively. The influence of the temperature gradient is modeled as the change of the lubrication oil viscosity and the length variation of the clearance due to the cryogenic thermal expansion of the journal. The analytical expressions of the tilting pad bearing oil-film force are then amended and substitute into the lumped parameter model of the turbo-expander rotor dynamics. Linear analysis based on this model indicates that the existence of the temperature gradient can stabilize the turbo-expander rotor system to an extent, while the nonlinear analyses reveal that the temperature gradient will advance the occurrence of the quasi-periodic motion and break the equilibrium of the vibration between the expander side and the compressor side. Furthermore, an experimental system is established and the experimental results show that the temperature of the tilting pad bearing is influenced by the environment temperature greatly; the spectrum of the displacement of the rotor is dominated by the synchronous frequency of the impellers and bearings. The experiment results also observe the vibration amplitude decreases when the environment temperature gets down and grows when the rotating speed increases. At the same time, the sensitivity of the vibration amplitude versus rotating speed decreases as the environment temperature rises, and vice versa.
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Shin, Dongil, Alan B. Palazzolo et Xiaomeng Tong. « Squeeze Film Damper Suppression of Thermal Bow-Morton Effect Instability ». Journal of Engineering for Gas Turbines and Power 142, no 12 (1 décembre 2020). http://dx.doi.org/10.1115/1.4048602.
Texte intégralRésumé :
Abstract The Morton effect (ME) is a synchronous vibration problem in turbomachinery caused by the nonuniform viscous heating around the journal circumference, and its resultant thermal bow (TB) and ensuing synchronous vibration. This paper treats the unconventional application of the SFD for the mitigation of ME-induced vibration. Installing a properly designed squeeze film damper (SFD) may change the rotor's critical speed location, damping, and deflection shape, and thereby suppress the vibration caused by the ME. The effectiveness of the SFD on suppressing the ME is tested via linear and nonlinear simulation studies employing a three-dimensional (3D) thermohydrodynamic (THD) tilting pad journal bearing (TJPB), and a flexible, Euler beam rotor model. The example rotor model is for a compressor that experimentally exhibited an unacceptable vibration level along with significant journal differential heating near 8000 rpm. The SFD model includes fluid inertia and is installed on the nondrive end bearing location where the asymmetric viscous heating of the journal is highest. The influence of SFD cage stiffness is evaluated.
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Benti, Gudeta Berhanu, David Rondon, Rolf Gustavsson et Jan-Olov Aidanpää. « Numerical and Experimental Study on the Dynamic Bearing Properties of a Four-Pad and Eight-Pad Tilting Pad Journal Bearings in a Vertical Rotor ». Journal of Energy Resources Technology 144, no 1 (24 août 2021). http://dx.doi.org/10.1115/1.4052032.
Texte intégralRésumé :
Abstract In this paper, the dynamics of tilting pad journal bearings (TPJB) with four and eight pads are studied and compared experimentally and numerically. The experiments are performed on a rigid vertical rotor supported by two identical bearings. Two sets of experiments are carried out under a similar test setup. One set is performed on a rigid rotor with two four-pad bearings, while the other is on a rigid rotor with two eight-pad bearings. The dynamic properties of the two bearing types are compared with each other by studying the unbalance response of the system at different rotor speeds. Numerically, the test rig is modeled as a rigid rotor and the bearing coefficients are calculated based on Navier–Stokes equation. A nonlinear bearing model is developed and used in the steady-state response simulation. The measured and simulated displacement and force orbits show similar patterns for both bearing types. Compared to the measurement, the simulated mean value and range (peak-to-peak amplitude) of the bearing force deviate with a maximum of 16% and 38%, respectively. It is concluded that, unlike the eight-pad TPJB, the four-pad TPJB excites the system at the third- and fifth-order frequencies, which are due to the number of pads, and the amplitudes of these frequencies increase with the rotor speed.
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Varela, Alejandro Cerda, et Ilmar Ferreira Santos. « Tilting-Pad Journal Bearings With Active Lubrication Applied as Calibrated Shakers : Theory and Experiment ». Journal of Vibration and Acoustics 136, no 6 (24 septembre 2014). http://dx.doi.org/10.1115/1.4028452.
Texte intégralRésumé :
In recent years, a continuous research effort has transformed the conventional tilting-pad journal bearing (TPJB) into a mechatronic machine element. The addition of electromechanical elements provides the possibility of generating controllable forces over the rotor as a function of a suitable control signal. Such forces can be applied in order to perform parameter identification procedures “in situ,” which enables evaluation of the mechanical condition of the machine in a noninvasive way. The usage of a controllable bearing as a calibrated shaker requires obtaining the bearing specific frequency dependent calibration function, i.e., the transfer function between control signal and force over the rotor. This work presents a theoretical model of the calibration function for a TPJB with active lubrication. The bearing generates controllable forces by injecting pressurized oil directly into the bearing clearance. The injected flow is controlled by means of a servovalve. The theoretical model includes the dynamics of the hydraulic system using a lumped parameter approach, which is coupled with the bearing oil film using a modified form of the Reynolds equation. The oil film model is formulated considering an elastothermohydrodynamic lubrication regime. New contributions to the mathematical modeling are presented, such as the inclusion of the dynamics of the hydraulic pipelines and the obtention of the bearing calibration function by means of harmonic analysis of a linearized form of the controllable bearing constitutive equations. The mathematical model is used to study the relevance and effects of different parameters on the calibration function, aiming at providing general guidelines for the active bearing design. Finally, experimental results regarding the calibration function and the usage of the studied bearing as a calibrated shaker provide insight into the possibilities of application of this technology.
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Ryu, Keun, et Zachary Ashton. « Bump-Type Foil Bearings and Flexure Pivot Tilting Pad Bearings for Oil-Free Automotive Turbochargers : Highlights in Rotordynamic Performance ». Journal of Engineering for Gas Turbines and Power 138, no 4 (13 octobre 2015). http://dx.doi.org/10.1115/1.4031440.
Texte intégralRésumé :
Oil-free turbochargers (TCs) require gas bearings in compact units of enhanced rotordynamic stability, mechanical efficiency, and improved reliability with reduced maintenance costs compared with oil-lubricated bearings. Implementation of gas bearings into automotive TCs requires careful thermal management with accurate measurements verifying model predictions. Gas foil bearings (GFBs) are customarily used in oil-free microturbomachinery because of their distinct advantages including tolerance to shaft misalignment and centrifugal/thermal growth, and large damping and load capacity compared with rigid surface gas bearings. Flexure pivot tilting pad bearings (FPTPBs) are widely used in high-performance turbomachinery since they offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability. The paper details the rotordynamic performance and temperature characteristics of two prototype oil-free TCs; one supported on foil journal and thrust bearings and the other one is supported on FPTP journal bearings and foil thrust bearings of identical sizes (outer diameter (OD) and inner diameter (ID)) with the same aerodynamic components. The tests of the oil-free TCs, each consisting of a hollow rotor (∼0.4 kg and ∼23 mm in OD at the bearing locations), are performed for various imbalances in noise, vibration, and harshness (NVH; i.e., cold air driven rotordynamics rig) and gas stand test facilities up to 130 krpm. No forced cooling air flow streams are supplied to the test bearings and rotor. The measurements demonstrate the stable performance of the rotor–gas bearing systems in an ambient NVH test cell with cold forced air into the turbine inlet. Post-test inspection of the test FPTPGBs after the hot gas stand tests evidences seizure of the hottest bearing, thereby revealing a notable reduction in bearing clearance as the rotor temperature increases. The compliant FPTPGBs offer a sound solution for stable rotor support only at an ambient temperature condition while demonstrating less tolerance for shaft growth, centrifugal, and thermal, beyond its clearance. The current measurements give confidence in the present GFB technology for ready application into automotive TCs for passenger car and commercial vehicle applications with increased reliability.
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G. Salazar, Jorge, et Ilmar F. Santos. « On the Controllability and Observability of Actively Lubricated Journal Bearings With Pads Featuring Different Nozzle-Pivot Configurations ». Journal of Tribology 139, no 3 (10 octobre 2016). http://dx.doi.org/10.1115/1.4033053.
Texte intégralRésumé :
The fundamental properties of an actively lubricated bearing (ALB) from a control viewpoint are investigated, i.e., the stability, controllability and observability. The ALB involves the addition of an oil injection system to the standard tilting-pad journal bearing (TPJB) to introduce constantly and/or actively high pressurized oil into the rotor-pad gap through, commonly, a single radial nozzle. For the work goal, a four degrees-of-freedom (DOFs) ALB system linking the mechanical with the hydraulic dynamics is presented and studied, comprising: (i) the vertical journal movement, (ii) the pad tilt angle, (iii) the vertical pad movement—due to the pivot flexibility, and (iv) the controllable force as the hydraulic DOF. The test rig consists of a rigid rotor supported by a single rocker-pivoted rigid pad. A thorough parametric study is carried out by investigating the effects of: (a) nozzle-pivot offset, (b) pivot flexibility, and (c) bearing loading on these control basics in order to determine the pad with the best control characteristics. Different nozzle-pivot offsets can be set by varying the positioning of either the injection nozzle or the pivot line. The influence of the pivot compliance on the bearing dynamics is assessed by benchmarking the results obtained with the flexible pivot against the rigid pivot. Three different bearing loads are studied. According to the results, the proposed configurations, especially the offset-pivot pad with slight offsets, improve the bearing control characteristics by introducing an extra mechanism to access the system states. The loading condition modifies the stability, controllability, and observability, while the pivot flexibility highly affects the ALB dynamics.
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Rindi, A., L. Baldassarre, D. Panara, E. Meli, A. Ridolfi, A. Frilli, D. Nocciolini et S. Panconi. « An Efficient Iterative Approach for the Analysis of Thermal Instabilities in Rotating Machines ». Journal of Vibration and Acoustics 139, no 6 (17 août 2017). http://dx.doi.org/10.1115/1.4037143.
Texte intégralRésumé :
Most of the technological developments achieved in the turbomachinery field during the last years have been obtained through the introduction of fluid dynamic bearings, in particular tilting pad journal bearings (TPJBs). However, even those bearings can be affected by thermal instability phenomena as the Morton effect at high peripheral speeds. In this work, the authors propose a new iterative finite element method (FEM) approach for the analysis of those thermal–structural phenomena: the proposed model, based on the coupling between the rotor dynamic and the thermal behavior of the system, is able to accurately reproduce the onset of thermal instabilities. The authors developed two versions of the model, one in the frequency domain and the other in the time domain; both models are able to assure a good tradeoff between numerical efficiency and accuracy. The computational efficiency is critical when dealing with the typical long times of thermal instability. The research activity has been carried out in cooperation with General Electric Nuovo Pignone SPA, which provided both the technical and experimental data needed for the model development and validation.
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Dimond, Timothy W., Amir A. Younan et Paul Allaire. « Comparison of Tilting-Pad Journal Bearing Dynamic Full Coefficient and Reduced Order Models Using Modal Analysis (GT2009-60269) ». Journal of Vibration and Acoustics 132, no 5 (26 août 2010). http://dx.doi.org/10.1115/1.4001507.
Texte intégralRésumé :
There is a significant disagreement in the literature concerning the proper evaluation of the experimental identification and frequency response of tilting-pad journal bearings (TPJBs) due to shaft excitations. Two linear models for the frequency dependence of TPJBs have been proposed. The first model, the full coefficient or stiffness-damping (KC) model, considers Np tilting pads and two rotor radial motions for Np+2 degrees of freedom. The dynamic reduction of the KC model results in eight frequency-dependent stiffness and damping coefficients. The second model, based on bearing system identification experimental results, employs 12 frequency-independent stiffness, damping, and mass (KCM) coefficients; pad degrees of freedom are not considered explicitly. Experimental data have been presented to support both models. There are major differences in the two approaches. The present analysis takes a new approach of considering pad dynamics explicitly in a state-space modal analysis. TPJB shaft and bearing pad stiffness and damping coefficients are calculated using a well known laminar, isothermal analysis and a pad assembly method. The TPJB rotor and pad KC model eigenvalues and eigenvectors are then evaluated using state-space methods, with rotor and bearing pad inertias included explicitly in the model. The KC model results are also nonsynchronously reduced to the eight stiffness and damping coefficients and are expressed as shaft complex impedances. The system identification method is then applied to these complex impedances, and the state-space modal analysis is applied to the resulting KCM model. The damping ratios, natural frequencies, and mode shapes from the two bearing representations are compared. Two sample TPJB cases are examined in detail. The analysis indicated that four underdamped modes, two forward and two backward, dominate the rotor response over excitation frequencies from 0 to approximately running speed. The KC model predicts additional nearly critically damped modes primarily involving pad degrees of freedom, which do not exist in the identified KCM model. The KCM model results in natural frequencies that are 63–65% higher than the KC model. The difference in modal damping ratio estimates depends on the TPJB considered; the KCM estimate was 7–17% higher than the KC model. The results indicate that the KCM system identification method results in a reduced order model of TPBJ dynamic behavior, which may not capture physically justifiable results. Additionally, the differences in the calculated system natural frequency and modal damping have potential implications for rotordynamic analyses of flexible rotors.
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Jensen, Kenneth M., et Ilmar F. Santos. « Design of actively-controlled oil lubrication to reduce rotor-bearing-foundation coupled vibrations - theory & ; experiment ». Proceedings of the Institution of Mechanical Engineers, Part J : Journal of Engineering Tribology, 30 mai 2022, 135065012211006. http://dx.doi.org/10.1177/13506501221100615.
Texte intégralRésumé :
This paper gives theoretical and experimental contributions to the field of tribotronics, linking i) tribology of fluid film bearings, ii) flexible rotor and flexible foundation dynamics, iii) sensing systems, iv) fluid power and hydraulic actuator dynamics, and v) control theory in a holistic way. Based on a multi-physical modelling approach, a mathematical model (digital twin) is derived coupling the subsystems from i) till v). The digital twin is employed to design and optimize the feedback control system of an actively-controlled tilting pad journal bearing with the aim of attenuating vibration levels of the rotor-bearing-foundation system. The feedback control system is experimentally implemented and tested on a test rig. Significant reduction of the rotor-bearing-foundation vibrations is achieved in the frequency range of 20 until 250 Hz. Very good agreement between theory and experiment is achieved at the low rotor angular velocity used. The theoretical and experimental outcomes of the paper suggest that vi) the thermal domain needs to be included in the multi-physical modelling approach to accurately represent the bearing properties under thermoelastohydrodynamic conditions and expand the theoretical and experimental approaches to higher angular velocities.
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Luneno, Jean-Claude, Jan-Olov Aidanpää et Rolf Gustavsson. « Model Based Analysis of Coupled Vibrations Due to the Combi-Bearing in Vertical Hydroturbogenerator Rotors ». Journal of Vibration and Acoustics 133, no 6 (28 novembre 2011). http://dx.doi.org/10.1115/1.4005002.
Texte intégralRésumé :
The studies presented in this paper focus on analyzing how the combined thrust-journal bearing (commonly called combi-bearing) influences the dynamics of hydropower rotors. Thrust bearing is a component used in vertical rotating machinery and shafts designed to transmit thrust. The total axial load is carried by the single thrust bearing. Any design, manufacture, or assembly error in this component (thrust bearing) would certainly influence the functionality of the entire machine. The analyzed combi-bearing is an existing machine component used in the hydropower unit Porjus U9 situated in northern Sweden. This combi-bearing is a fluid-film lubricated tilting-pad thrust and journal bearings combined together. Only linear fluid-film stiffness was taken into account in the model while fluid-film damping and pads inertia effects were not taken into account. The linearized model shows that the combi-bearing couples the rotor’s lateral and angular motions. However, if the thrust bearing’s pads arrangement is not symmetrical or if all the pads are not angularly equidistant the rotor axial and angular motions are also coupled. This last case of coupling will also occur if the thrust bearing equivalent total stiffness is not evenly distributed over the thrust bearing. A defective pad or unequal hydrodynamic pressure distribution on the pads’ surfaces may be the cause. The Porjus U9’s simulation results show that the combi-bearing influences the dynamic behavior of the machine. The rotor motions’ coupling due to combi-bearing changes the system’s natural frequencies and vibration modes.
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Avendano, Raul D., et Dara W. Childs. « One Explanation for Two-Times Running Speed Response Due to Misalignment in Rotors Connected by Flexible Couplings ». Journal of Engineering for Gas Turbines and Power 135, no 6 (20 mai 2013). http://dx.doi.org/10.1115/1.4023232.
Texte intégralRésumé :
Misalignment in turbomachinery is commonly thought to produce two-times running-speed (2N) response. The source of 2N vibration response was investigated, starting with the development of finite-element models for three flexible disk-pack couplings (four-bolt, six-bolt, and eight-bolt couplings). Parallel and angular misalignments were analyzed. The resultant lateral stiffness terms had 1N, 2N, and 3N harmonic components versus the shaft rotation angle. The four-bolt coupling had large 1N stiffness components under angular and parallel misalignment. The six-bolt coupling had only a 1N reaction component under angular misalignment, while parallel misalignment showed a strong 2N reaction component, larger than either the 1N or 3N components. Under angular misalignment, the eight-bolt model produced large 1N reaction components. Under parallel misalignment, it produced 1N, 2N, and 3N components that were similar in magnitude. All the couplings behaved linearly in the range studied. Some experts attribute observed 2N response to nonlinear bearing forces produced by bearings at high unit loads. Static tests for a five-pad tilting-pad journal bearing with unit loads up to 34.5 bars produced small 2N motion components that did not grow with increasing unit load. A Jeffcott-rotor model with shaft stiffness orthotropy and a fixed-direction side load predicts that 2N response depends on three related factors: (1) the degree of orthotropy (the 1N stiffness variation magnitude), (2) the magnitude of the side load, and (3) the relative ratio of running speed to rotor first natural frequency, (ω/ωn). The 2N response magnitude is largest when ω is close to ωn/2. The side load is required to create 2N response due to shaft stiffness orthotropy. Misaligned couplings create precisely the same (very old) physical model as a two-pole turbogenerator rotor with a gravity side load (gravity critical speed). The response of a two-rotor/coupling system with parallel and angular misalignment was simulated using a time-transient code. When the frequency ratio was 0.5, the system response with the four-bolt and six-bolt coupling had a synchronous 1N component as well as a significant 2N component. Parallel misalignment at a coupling produces stiffness orthotropy and a fixed-direction side load. For ranges of running speed near ωn/2, these two elements can combine to produce 2N response.