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Title: New developments in experimental analysis of torsional vibration for rotating shaft systems
Authors: Miles, Toby J.
Issue Date: 1997
Publisher: © Toby Miles
Abstract: The torsional vibration of rotating shafts contributes significantly to machinery vibration and noise but is notoriously difficult to study experimentally. New developments are reported which address the need for appropriate measurement tools, through improved understanding of the laser torsional vibrometer (LTV) and the application of modal analysis techniques. The LTV was developed previously for non-contact measurement of torsional oscillation. This thesis describes comprehensive theory to account for the sensitivity of its measurements to shaft motion in all degrees of freedom. The significance of this sensitivity is compared with the instrument noise floor and typical torsional and lateral vibration levels. Optimum instrument alignments are thereby specified to ensure immunity to all lateral motion. A new technique is proposed permitting unambiguous measurement in situations where conventional use of an LTV shows unavoidable lateral vibration sensitivity. Simultaneously, a previously unattained measurement of shaft bending vibration is derived. Practical application is demonstrated with measurements from an engine crankshaft, with identification of the first bending mode and estimation of its bending vibration amplitude. Experimental torsional modal analysis on rotating systems has had limited progression due to the absence of a versatile means to apply an instrumented torque. A novel device has been developed to provide a controllable and measurable torsional excitation, based on the principle of eddy current braking. Together with an LTV to measure response, estimation of the torque input permits frequency response functions to be obtained without modification to the system under test. This system achieves full modal analysis from a rotating shaft using conventional techniques for data processing, with derivation of natural frequencies, mode shapes and damping factors. Results from simple shaft systems consider the variation of modal parameters under rotating conditions. Application of this technology is clearly demonstrated in studying the behaviour of a centrifugal pendulum vibration absorber (CPV A) used to control the resonant modes of a shaft system. Accurate measurement of each individual pendulum tuning is achieved. with examination of other effects related to successful absorber design. These results are complemented by novel use of the LTV to study the actual pendulum motion. The depth of information obtained underlines the analysis potential made possible by these advances in torsional vibration measurement.
Description: A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/10635
Appears in Collections:PhD Theses (Mechanical, Electrical and Manufacturing Engineering)

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