Rotordynamics

The modelling of rotors and their associated support structures has been developed to a high degree of sophistication over the past twenty years especially by the use of finite element analysis. Accurate models are invaluable in the resolution of a wide variety of rotor dynamic problems and are often required in connection with computerised monitoring for the detection and diagnosis of faults. The validation of these models is performed by comparing numerical eigendata with the natural frequencies, mode shapes and critical speeds acquired from vibration tests of a physical structure. Alternatively measured run-down data, i.e. the response of the system as the speed of the rotor is reduced, may be compared to numerical predictions.

There is considerable interest in improving the correlation between numerical and test results. The shaft can usually be modelled accurately and speed dependent bearing stiffness and damping coefficients may also be estimated. The foundation is often a complex steel framework, the modelling of which is time consuming and difficult. A well tuned model would add significantly to the speed and efficiency of the resolution of in-service problems. However, a number of instances have occurred in which current models have been insufficiently accurate to be used to reliably isolate the source of a problem. These instances have occurred when the machine foundations have played a significant role in the dynamics of the machine.

The present day requirement for ever-increasing reliability in the field of rotor dynamics is now more important than ever before and continues to grow constantly. Advances are continually being made in this area, due largely to the consistent demand from the power-generation and transportation industries. Because of progress made in engineering and materials science, rotating machinery is becoming both faster and lighter, as well as being required to run for longer periods of time. All of these factors mean that the detection, location and analysis of faults play a vital role in the field of rotor dynamics.

One of the major areas of interest in the modern-day condition monitoring of rotating machinery is that of vibration. If a fault develops and goes undetected, then, at best, the problem will not be too serious and can be remedied quickly and cheaply; at worst, it may result in expensive damage and down-time, injury, or even loss of life. By measurement and analysis of the vibration of rotating machinery, it is possible to detect and locate important faults such as mass unbalance, shaft bow, rub and cracked shafts.

Selected References

Identification of Foundation and Bearing Models

R Tiwari, AW Lees & MI Friswell, Identification of Bearing Dynamic Parameters: A Review. Shock and Vibration Digest, 36(2), March 2004, 99-124.

R Tiwari, AW Lees & MI Friswell, Identification of Speed-Dependent Bearing Parameters. Journal of Sound and Vibration, 254(5), July 2002, 967-986.

MG Smart, MI Friswell & AW Lees, Estimating Turbogenerator Foundation Parameters - Model Selection and Regularisation. Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences, 456, No. 1999, July 2000, 1583-1607.

MG Smart, MI Friswell, AW Lees & U Prells, Estimating Turbo-Generator Foundation Parameters. IMechE Journal of Engineering Science, 212(C8), 1998, 653-665.

Fault Diagnosis

AW Lees & MI Friswell, Where Next for Condition Monitoring of Rotating Machinery? Advances in Vibration Engineering, 5(4), 2006, 263-277.

JK Sinha, AW Lees & MI Friswell, Estimating Unbalance and Misalignment of a Flexible Rotating Machine from a Single Run-Down. Journal of Sound and Vibration, 272(3-5), May 2004, 967-989.

AW Lees, JK Sinha & MI Friswell, The Identification of the Unbalance of a Flexible Rotating Machine from a Single Run-Down. ASME Journal of Engineering for Gas Turbines & Power, 126(2), April 2004, 416-421.

JK Sinha, MI Friswell & AW Lees, The Identification of the Unbalance and the Foundation Model of a Flexible Rotating Machine from a Single Run-Down. Mechanical Systems and Signal Processing,16(2-3), March 2002, 255-271

S Edwards, AW Lees & MI Friswell, Experimental Identification of Excitation and Support Parameters of a Flexible Rotor-Bearings-Foundation System from a Single Run-Down. Journal of Sound and Vibration, 232(5), May 2000, 963-992.

S Edwards, AW Lees & MI Friswell, The Influence of Torsion on Rotor-Stator Contact in Rotating Machinery. Journal of Sound and Vibration, 225(4), August 1999, 767-778.

S Edwards, AW Lees & MI Friswell, Fault Diagnosis of Rotating Machinery. Shock and Vibration Digest, 30(1), January 1998, 4-13.

AW Lees & MI Friswell, The Evaluation of Rotor Imbalance in Flexibly Mounted Machines. Journal of Sound and Vibration, 208(5), December 1997, 671-683.

General Analysis of Rotating Machinery

MI Friswell, JT Sawicki, DJ Inman & AW Lees, The Response of Rotating Machines on Viscoelastic Supports. International Review of Mechanical Engineering, 1(1), January 2007, 32-40.

SD Garvey, MI Friswell, EJ Williams, AW Lees & I Care, Robust Balancing for Rotating Machines. IMechE Journal of Engineering Science, 216(11), November 2002, 1117-1130.

MI Friswell, JET Penny, SD Garvey & AW Lees, Damping Ratio and Natural Frequency Bifurcations in Rotating Systems. Journal of Sound and Vibration, 245(5), August 2001, 960-967.

MI Friswell, SD Garvey, JET Penny & MG Smart, Computing Critical Speeds for Rotating Machines with Speed-Dependent Bearing Properties. Journal of Sound and Vibration, 213(1), May 1998, 139-158.


Last updated February 2009 by M I Friswell