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Content archived on 2024-04-19



The MARS project has developed a set of experimental and analytical techniques for measuring and predicting the dynamic behaviour of rotating machine structures, including flexible rotors, foundations and bearing elements.

An excitation system using Active Magnetic Bearings (AMBs) with integral Hall effect force sensors has been developed to supply a controlled sine wave force pattern in the vertical and horizontal directions at each bearing. They allow selective excitation of forward and backward modes of the rotating rotor. An identification algorithm for AMB machinery was developed. Controller design methodology for AMB machinery was further developed.

A shaft-synchronised scanning laser doppler vibrometer has been developed for response measurements enabling motion of a single point on a rotating disc to be measured. Measurements from an array of proximity probes have been used to determine the travelling wave information from a rotating shaft or disc and the wave motion may be displayed in a multi-directional form of Campbell diagram.

A pc based modal testing data acquisition and control package has been developed which will adjust the horizontal and vertical forces applied by the two AMBs to provide a set of four sine wave force patterns, even when the structure and excitation system are non-linear. The responses can be separated to determine the Frequency Response functions (FRFs) due to a single force. Accurate measurements can be made, even in the presence of noise from the transducers, or due to additional synchronous response in the rotor.

A new Finite Element programme LISA has been specifically developed for analysing rotor dynamics. The programme interfaces with other packages (NASTRAN, PATRAN & MATLAB), but allows easy modelling of specific rotor dynamics problems such as gyroscopic and centrifugal effects, and the modelling of bearings and seals. High quality graphical output is provided as spatial mode shape displays, frequency response functions or time responses.

A two-stage approach to Model Updating of the FE model, based on non-rotating and rotating FRFs has been developed which may be used to determine properties such as dynamic bearing stiffnesses, or the gyroscopic coupling. These measurement, analysis and modelling techniques have been demonstrated on a specially designed rotating machine model used to investigate a series of parameters: flexible rotors and stators, foundations and bearing elements, that have major influence on the dynamic properties of rotating machines.
The effective design of high-speed rotating machines requires a range of prediction and analysis tools which may be used with confidence to assess performance before manufacture. The accuracy of design assessments based on simple mathematical is often inadequate, especially with rotating components and a more reliable structural dynamic analysis modelling procedure than is currently available for predicting fatigue life, stability and vibration levels is now required.

This project focuses on the fundamental engineering principles involved in the dynamic modelling of rotating structures. The accuracy of this modelling will be checked by validation against measured data from a specially-designed rotating component test rig using new and innovative test methods. The project will explore and evaluate new vibration test methods using non-contacting excitation devices and non-contacting measurement transducers for the rotating elements. This will permit the comparison and updating of the theoretical predictions using the measured properties.

Overall, the project will improve the understanding of the modelling problems inherent in rotating machines, improve measurement techniques and increase the confidence with which FE models can be updated with accurate modal test data.

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