Modal Response of a Flexible Rotor in Fluid-Film Bearings

1974 ◽  
Vol 96 (2) ◽  
pp. 525-533 ◽  
Author(s):  
J. W. Lund
Keyword(s):  
Fluid Film ◽  
Mode Shapes ◽  
Flexible Rotor ◽  
First Order ◽  
Fluid Film Bearings ◽  
Modal Response ◽  
Governing System ◽  
System Equations ◽  
Multistage Compressor ◽  
Modal Method

An analysis is presented for calculating the response of a general flexible rotor in fluid-film bearings to forced and transient excitation. It is a modal method where the governing system equations are transformed by means of normal coordinates into a set of decoupled, first-order equations which can be solved in closed form. The transformation is based on the orthogonal complex modal functions (“mode shapes”) associated with the eigenvalues of the system. The method has been applied to an industrial multistage compressor. Numerical results are given for the response to selected unbalance distributions and, also, the transient response to a shock pulse.

Stability and Damped Critical Speeds of a Flexible Rotor in Fluid-Film Bearings

1974 ◽  
Vol 96 (2) ◽  
pp. 509-517 ◽  
Author(s):  
J. W. Lund
Keyword(s):  
Dynamic Properties ◽  
Fluid Film ◽  
Internal Damping ◽  
Flexible Rotor ◽  
Critical Speeds ◽  
Damping Coefficients ◽  
Fluid Film Bearings ◽  
Multistage Compressor ◽  
Stiffness And Damping ◽  
Rotor Model

A method is described for calculating the threshold speed of instability and the damped critical speeds of a general flexible rotor in fluid-film journal bearings. It is analogous to the Myklestad-Prohl method for calculating critical speeds and is readily programmed for numerical computation. The rotor model can simulate any practical shaft geometry and support configuration. The bearings are represented by their linearized dynamic properties, also known as the stiffness and damping coefficients of the bearing, and the calculation includes hysteretic internal damping in the shaft and destabilizing aerodynamic forces. To demonstrate the application of the method, results are shown for an industrial, multistage compressor.

Identification of Bearing Force Coefficients From Measurements of Imbalance Response of a Flexible Rotor

2004 ◽  
Author(s):  
Luis San Andre´s ◽  
Oscar C. De Santiago
Keyword(s):  
High Performance ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Simple Method ◽  
Force Coefficients ◽  
Fluid Film Bearings ◽  
Support Force ◽  
Bearing Force ◽  
Rotor Structure ◽  
Motion Amplitude

Field identification of fluid film bearing parameters is critical for adequate interpretation of rotating machinery performance and necessary to validate or calibrate predictions from restrictive computational fluid film bearing models. This paper presents a simple method for estimating bearing support force coefficients in flexible rotor-bearing systems. The method requires two independent tests with known mass imbalance distributions and the measurement of the rotor motion (amplitude and phase) at locations close to the supports. The procedure relies on the modeling of the rotor structure and finds the bearing transmitted forces as a function of observable quantities (rotor vibrations at bearing locations). Imbalance response measurements conducted with a two-disk flexible rotor supported on two-lobe fluid film bearings allow validation of the identification method estimations. Predicted (linearized) bearing force coefficients agree reasonably well with the parameters derived from the test data. The method advanced neither adds mathematical complexity nor requires additional instrumentation beyond that already available in most high performance turbomachinery.

The Lower Bound of the Stability Threshold Speed of a Flexible Rotor System in Fluid-Film Bearings

1989 ◽  
Vol 111 (3) ◽  
pp. 351-353
Author(s):  
Wen Zhang
Keyword(s):  
Lower Bound ◽  
Theoretical Foundation ◽  
Simple Approach ◽  
Rotor System ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Stability Threshold ◽  
Fluid Film Bearings ◽  
Single Disk ◽  
The Stability

The paper is devoted to the estimation of the lower bound of the stability threshold speed (STS) of a flexible rotor system supported in fluid-film bearings. It is proved theoretically that the STS of any multi-degree-of-freedom flexible rotor system is always higher than the STS of the corresponding equivalent single disk rotor. The conclusion offers us a simple approach to estimate the STS of any actual rotor system and provides a theoretical foundation for the approach.

On the vibration and control of a flexible rotor mounted on fluid film bearings

1997 ◽  
Vol 65 (6) ◽  
pp. 849-856 ◽  
Author(s):  
Z. Abduljabbar ◽  
M.M. ElMadany ◽  
E. Al-Bahkali
Keyword(s):  
Fluid Film ◽  
Flexible Rotor ◽  
Fluid Film Bearings ◽  
And Control

Field Identification of Stiffness and Damping Characteristics of Fluid Film Bearings

2008 ◽  
Author(s):  
Sameh H. Tawfick ◽  
Aly El-Shafei ◽  
M. O. A. Mokhtar
Keyword(s):  
Journal Bearings ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Test Rig ◽  
Vibration Data ◽  
Damping Characteristics ◽  
Fluid Film Bearings ◽  
Field Identification ◽  
Modal Mass ◽  
Stiffness And Damping

A method for field identification of stiffness and damping characteristics of fluid film bearings FFB is derived. The method relies on measuring both the shaft and the housing’s vibration response. Two independent unbalance runs are performed and the synchronous response is recorded. Using the housing vibration data, the amount of unbalance acting on the bearing, as well as the flexible shafts’ “modal mass” can be experimentally determined. Thus, with this method, field engineers can identify the bearings impedance in flexible rotor-bearing systems. A test rig comprising a flexible shaft supported on two cylindrical journal bearings is used to verify the proposed method. The amount of uncertainty in the derived coefficients is calculated.

Jorgen W. Lund: Theories Versus Tests

2001 ◽  
Author(s):  
Jorgen Tonnesen
Keyword(s):  
Thermal Properties ◽  
Experimental Work ◽  
Rotor Dynamics ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Late Professor ◽  
Fluid Film Bearings ◽  
Condensed Form ◽  
Flexible Rotors ◽  
Rotor Balancing

Abstract The contribution of the late Professor Jorgen W. Lund in the field of rotor dynamics and fluid film bearings is presented in a condensed form with the emphasis on the experimental work and results that confirm and support many of Dr. Lund’s theories and analyses. Included are subjects of rotor balancing by the influence method, unbalance response of a flexible rotor, damped critical speeds of flexible rotors and fluid film bearing’s static, dynamic and thermal properties.

Unbalance Response of an Elastic Rotor in Damped Flexible Bearings at Supercritical Speeds

1971 ◽  
Vol 93 (2) ◽  
pp. 265-275 ◽  
Author(s):  
Neville F. Rieger
Keyword(s):  
Critical Speed ◽  
Mode Shapes ◽  
Rotor Speed ◽  
Flexible Rotor ◽  
Relative Stiffness ◽  
Unbalance Response ◽  
Fluid Film Bearings ◽  
Transmitted Force ◽  
Rotor Mass ◽  
Bearing System

The unbalance response of a uniform flexible rotor in fluid-film bearings has been analyzed for speeds up to 20 times the lowest rigid-bearing critical speed. Rotor mass and elasticity are distributed uniformly along the length of the rotor. A single radial speed-dependent force is used to represent the rotor unbalance. The rotor is assumed to operate in stable plain cylindrical bearings which are represented by direct and cross-coupled spring and damping forces. The influence of rotor speed, bearing operating eccentricity, relative stiffness of rotor and bearings, and unbalance location along rotor on the performance of the rotor-bearing system has been determined. Results are presented as charts of rotor maximum whirl amplitude and of bearing maximum whirl transmitted force for wide ranges of the foregoing parameters. Mode shapes at critical speeds are also included.

scholarly journals Uncertainty analysis of a flexible rotor supported by fluid film bearings

2015 ◽  
Vol 12 (8) ◽  
pp. 1487-1504 ◽  
Author(s):  
Aldemir Ap Cavalini Jr. ◽  
Fabian Andres Lara-Molina ◽  
Thiago de Paula Sales ◽  
Edson Hideki Koroishi ◽  
Valder Steffen Jr.
Keyword(s):  
Uncertainty Analysis ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Fluid Film Bearings
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