On the Transient Analysis of Rotor-Bearing Systems

1988 ◽  
Vol 110 (4) ◽  
pp. 515-520 ◽  
Author(s):  
R. Subbiah ◽  
N. F. Rieger
Keyword(s):  
Dynamic Systems ◽  
Transient Analysis ◽  
Element Model ◽  
Flexible Rotor ◽  
Rotor Systems ◽  
Response Data ◽  
Rotor Bearing ◽  
Time Marching ◽  
The Stability ◽  
The Given

The transient dynamic response of a flexible rotor in nonlinear supports has been investigated using time marching methods. Several marching techniques such as Newmark β, Wilson θ, and Houbolt have been utilized in this study of rotor-bearing dynamic systems, to examine the stability of the system, and the suitability of each technique for predicting the onset of instability. The given rotor system has been modeled both in space and time using the transfer matrix method and the Houbolt method. The transient orbital response data so obtained have been compared with those obtained by a finite element model. Differences in the order of 6 percent were found. A nonlinear representation of a finite bearing has been included in the transient matrix model and the stability characteristics of different rotor systems of varied complexity have been studied. The nonlinear results have been compared with earlier results obtained using linear bearing representations.

Coupling of Rotor-Gear-Casing Vibrations During Extreme Operating Events

1992 ◽  
Vol 114 (4) ◽  
pp. 464-471 ◽  
Author(s):  
F. K. Choy ◽  
J. Padovan ◽  
Y. F. Ruan
Keyword(s):  
Element Model ◽  
Operating Conditions ◽  
Transient Vibration ◽  
Rotor Systems ◽  
Power Plant Equipment ◽  
Modal Synthesis ◽  
Operating Environments ◽  
Rotor Bearing ◽  
The Matrix ◽  
Plant Equipment

During extreme operating environments (i.e., seismic events, base motion-induced vibrations, etc.), the coupled vibrations developed between the rotors, bearings, gears and enclosing structure of gear-driven rotating equipment can be quite substantial. Generally, such large vibrational amplitudes may lead to failures in both the rotor-gearing system and/or the casing structure. This paper simulates the dynamic behavior of rotor-bearing-gear system resulting from motion of the enclosed structure. The modal synthesis approach is used in this study to synthesize the dynamics of the rotor systems with the vibrations of their casing structure in modal coordinates. Modal characteristics of the rotor-bearing-gear systems are evaluated using the matrix transfer technique, while the modal parameters for the casing structure are developed through a finite element model using NASTRAN. The modal accelerations calculated are integrated through a numerical algorithm to generate modal transient vibration analysis. Vibration results are examined in both time and frequency domains to develop representations for the coupled dynamics generated during extreme operating conditions. Typical three-rotor bull gear-driven power plant equipment (compressors, pumps, etc.) is used as an example to demonstrate the procedure developed.

Updating Rotor-Bearing Finite Element Models

1997 ◽  
Author(s):  
Cristinel Mares ◽  
Cecilia Surace
Keyword(s):  
Finite Element ◽  
Element Model ◽  
Parameters Estimation ◽  
Flexible Rotor ◽  
Estimation Errors ◽  
Rotor Bearing ◽  
Bearing Stiffness ◽  
Measured Frequency Response ◽  
Stiffness And Damping ◽  
The Finite Element Model

Abstract In this paper, the possibility of updating the finite element model of a rotor-bearing system by estimating the bearing stiffness and damping coefficients from a few measured Frequency Response Functions using a Genetic Algorithm is investigated. The issues of identifiability and parameters estimation errors, computational costs and algorithm tuning are addressed. A simulated example of a flexible rotor supported by orthotropic bearings is used for illustrating the method.

Investigation on the stability of periodic motions of a flexible rotor-bearing system with two unbalanced disks

2014 ◽  
Vol 28 (7) ◽  
pp. 2561-2579 ◽  
Author(s):  
Chaofeng Li ◽  
Shihua Zhou ◽  
Shijie Jiang ◽  
Hexing Yu ◽  
Bangchun Wen
Keyword(s):  
Flexible Rotor ◽  
Periodic Motions ◽  
Rotor Bearing ◽  
The Stability ◽  
Bearing System

Use of dFRFs for Diagnosis of Asymmetric/Anisotropic Properties in Rotor-Bearing System

1996 ◽  
Vol 118 (1) ◽  
pp. 64-69 ◽  
Author(s):  
Chee-Young Joh ◽  
Chong-Won Lee
Keyword(s):  
Diagnostic Method ◽  
Experimental Results ◽  
Flexible Rotor ◽  
Coordinate Systems ◽  
Anisotropic Properties ◽  
Rotor Systems ◽  
Input And Output ◽  
Rotor Bearing ◽  
The Asymmetry ◽  
Bearing System

The diagnostic method, which utilizes the dFRFs defined in the stationary and rotating coordinate systems, is tested with a laboratory flexible rotor-bearing system, in order to verify its effectiveness in detection of the asymmetry in shaft and the anisotropy in stator. The experimental results indicate that the dFRFs can be effectively used for the diagnosis of anisotropy and/or asymmetry in rotor systems by the investigation of two kinds of dFRF estimates using the complex input and output signals defined in the stationary and rotating coordinate systems.

Effect of Flexible Damped Bearing-Supports on the Dynamic Stability of High-Speed Turbochargers

2013 ◽  
Author(s):  
A. Alsaeed ◽  
G. Kirk ◽  
S. Bashmal
Keyword(s):  
Dynamic Stability ◽  
Dynamic Characteristics ◽  
High Speed ◽  
Element Model ◽  
Dynamic Coefficients ◽  
Speed Range ◽  
Rotor Bearing ◽  
The Stability ◽  
The Finite Element Model ◽  
Bearing System

The aim of this study is to analytically design flexible damped bearing-supports in order to improve the dynamic characteristics of the rotor-bearing system. The finite-element model of the turbocharger rotor with linearized bearing dynamic coefficients is used to solve for the logarithmic decrements and hence the stability map. The design process attempts to find the optimum dynamic characteristics of the flexible damped bearing-support that would give best dynamic stability of the rotor-bearing system. The method is successful in greatly improving the dynamic stability of the turbocharger and may also lead to a total linear stability throughout the entire speed range when used besides the enhanced-performance hydrodynamic bearings.

Instability Due to Fluid Leakage of a Rotor System With Anisotropic Support

1989 ◽  
Vol 111 (1) ◽  
pp. 27-34
Author(s):  
J. H. Wang ◽  
M. T. Tsai
Keyword(s):  
Element Model ◽  
Point Of View ◽  
Simplified Model ◽  
Optimum Range ◽  
Fluid Leakage ◽  
Rotor Bearing ◽  
The Stability ◽  
Anisotropic Stiffness ◽  
The Finite Element Model ◽  
Bearing System

The instability caused by the fluid leakage leads to a limited performance of turbomachines. This instability may be improved by using flexible bearing supports with anisotropic stiffness. With a simplified model this effect is investigated including the influence of many parameters. The results show that the optimum range of anisotropy is strongly dependent on the parameters of rotor-bearing systems. In this paper an explanation from an energy point of view is presented to clarify the different stability behaviors with anisotropic bearing supports. Beside the simplified model, the stability of the complex rotor-bearing system with anisotropic bearing supports is investigated by the finite element model. An example of a typical 900 MW turbogenerator system is presented.

The Excitability of Flexible Rotors in Short Sleeve Bearings

1975 ◽  
Vol 97 (1) ◽  
pp. 105-115 ◽  
Author(s):  
E. J. Hahn
Keyword(s):  
Flexible Rotor ◽  
External Disturbances ◽  
Stability Threshold ◽  
Flexible Rotors ◽  
Rotor Bearing ◽  
Operating Regions ◽  
The Stability ◽  
Linearized Model ◽  
Lubricant Viscosity ◽  
Bearing System

Assuming the short bearing approximation and constant lubricant properties, the root loci of the pertinent characteristic function were obtained for the linearized model of a simple symmetric flexible rotor bearing system. Using these loci, design maps consisting of lines of constant damping and vibration frequency pertaining to the dominant roots are presented as a function of the equilibrium eccentricity ratio and a frequency parameter for relevant degrees of flexibility. These maps display undesirable operating regions where external disturbances such as shock or unbalance loading are likely to excite undesirable vibrations, as well as regions of instability. The maps may conveniently be used to determine the effect of changing journal speed, lubricant viscosity and/or bearing clearance. Increased flexibility is seen to reduce the stability threshold in a predictable manner and to reduce damping at the pin-pin critical speed. The approach is applicable to more complex rotor bearing systems. It is felt that the use of such maps will enhance the understanding of rotor bearing system behavior, particularly at operating regions close to the stability threshold.

Transient Response of Rotor-Bearing Systems

1974 ◽  
Vol 96 (2) ◽  
pp. 682-690 ◽  
Author(s):  
R. G. Kirk ◽  
E. J. Gunter
Keyword(s):  
Transient Response ◽  
Transient Analysis ◽  
Equations Of Motion ◽  
Present System ◽  
Flexible Rotor ◽  
Machine Performance ◽  
Extensive Evaluation ◽  
Rotor Bearing ◽  
Method Of Solution ◽  
Energy Principles

The equations of motion necessary to calculate the transient response of a multimass flexible rotor supported by nonlinear, damped bearings are derived from energy principles. Rotor excitation may be the result of imbalance, internal friction, rotor acceleration, nonlinear forces due to any number of bearing or seal stations, and gyroscopic couples developed from skewed disk effects. The method of solution for transient response simulation is discussed in detail and is based on extensive evaluation of numerical methods available for transient analysis. Examples of the application of transient response for the analysis of rotor bearing systems are presented and compared to actual machine performance. Recommendations for the use and extension of the present system simulation model are discussed.

Transient Analysis of an Asymmetric Rotor-Bearing System During Acceleration

1992 ◽  
Vol 114 (4) ◽  
pp. 465-475 ◽  
Author(s):  
An-Chen Lee ◽  
Yuan Kang ◽  
Kun-Lung Tsai ◽  
Kuo-Mo Hsiao
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Transient Analysis ◽  
Element Model ◽  
Dynamic Equations ◽  
Critical Speeds ◽  
Rotor Bearing ◽  
Asymmetric Rotor ◽  
The Finite Element Model ◽  
Bearing System

This paper deals with the transient vibration of asymmetric rotor systems during acceleration passing through several critical speeds at which synchronous or super-harmonic resonance occurs. The dynamic equations of the rotor-bearing system are formulated by the finite element model and the resulting dynamic equations are time-varying due to the effects of acceleration and asymmetry. In the formulation, a Timoshenko beam element is employed to simulate the rotating shaft and Eulerian angles are used to describe the orientations of the shaft element and disk. The numerical integration scheme for transient analysis is generated from the finite element model. Numerical examples are presented to illustrate (1) the effects of acceleration on peak amplitude and speed at which the peak occurs as the system passes through critical speeds, (2) the optimal acceleration process, which can be obtained by minimizing the peak response and the period of acceleration, (3) the speed regions where the transient instability exists.

scholarly journals On Using the Transfer Matrix Formulation for Transient Analysis of Nonlinear Rotor Bearing Systems

2004 ◽  
Vol 10 (6) ◽  
pp. 425-431 ◽  
Author(s):  
A. Liew ◽  
N. S. Feng ◽  
E. J. Hahn
Keyword(s):  
Steady State ◽  
Transfer Matrix ◽  
Transient Analysis ◽  
Vibration Response ◽  
Transient Solution ◽  
Matrix Formulation ◽  
Lumped Parameter ◽  
Deep Groove ◽  
Rotor Bearing ◽  
The Stability

For many years transfer matrices have been used to evaluate the steady-state vibration response of linear rotor bearing systems. More recently, they have been used to evaluate the steady-state periodic vibration response of nonlinear rotor bearing systems. For quasi-periodic and chaotic response, a transient solution is mandated and transient solution software can also be gainfully used to evaluate the stability of the above-mentioned periodic solutions. To date, transient solutions generally necessitate a different lumped parameter discretization of the rotor and involve solving simultaneously the differential equations for every degree of freedom. This article shows how transient analysis can be performed while maintaining the transfer matrix lumped parameter discretization. The technique is illustrated for a non symmetric unbalanced flexible rotor supported on hydrodynamic journal bearings or deep-groove ball bearings.

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