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Title: Angular (pitch and yaw) vibration measurements directly from rotors using laser vibrometry
Authors: Halkon, Ben J.
Rothberg, Steve
Keywords: Laser vibrometry
Angular
Vibration measurement
Surface roughness
Misalignment
Pseudo-vibration
Issue Date: 2014
Publisher: © Elsevier Ltd.
Citation: HALKON, B.J. and ROTHBERG, S.J. (2014) Angular (pitch and yaw) vibration measurements directly from rotors using laser vibrometry. Mechanical Systems and Signal Processing, 46 (2), pp.344-360
Abstract: Parallel beam laser vibrometers offer direct measurement of pitch and yaw vibration directly from rotors. This paper, intended as an essential guide for the practical parallel beam laser vibrometer practioner, presents exact mathematical expressions for measured angular velocity in the presence of inevitable misalignments and estimates the likely measurement error levels due to such misalignments as well as to other sources of uncertainty through numerical simulation. Cross-sensitivity to the orthogonal vibration component, i.e. cross-sensitivity in a pitch measurement to yaw motion and vice-versa, is confirmed for rough rotors whereas it is shown not to be present when rotors are polished-circular. A complementary experimental investigation of the relationship between surface roughness and cross-sensitivity confirms the identification of two preferred measurement configurations: from the side of a polished-circular rotor and from the end face of a (rough) rotor coated in retro-reflective tape. Rotors with surface roughness up to 50 nm satisfy the former case provided the vibration displacement at the rotor surface does not exceed 20% beam diameter. For surfaces with roughness of 10 nm this can be extended to 50%. For rough rotor end face measurements, post-processing is required to resolve the inherent cross-sensitivity; the need for post-processing is justified quantitatively through numerical simulation. Further simulations incorporating typical levels of instrument misalignment and measurement noise are used to enable quantification of the likely errors in such angular vibration measurements. For measurements from the side of a polished-circular rotor, errors are around 1% for amplitude and 10 mrad at integer orders affected by pseudo-vibration and around one-third of these levels elsewhere. For measurements from a rough rotor end face, errors will be similar at integer orders (from 2). Errors in the rotational speed measurement, required for post-processing, must be minimised in order to limit errors up to 2nd order while misalignments determine errors at around 0.4% amplitude and 4 mrad phase at orders above 2 other than at the integer orders.
Description: NOTICE: this is the author’s version of a work that was accepted for publication in Mechanical Systems and Signal Processing [© Elsevier] Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Mechanical Systems and Signal Processing, 46 (2), pp.344-360, doi: 10.1016/j.ymssp.2014.01.013
Version: Accepted for publication
DOI: 10.1016/j.ymssp.2014.01.013
URI: https://dspace.lboro.ac.uk/2134/14186
Publisher Link: http://dx.doi.org/10.1016/j.ymssp.2014.01.013
ISSN: 0888-3270
Appears in Collections:Published Articles (Mechanical, Electrical and Manufacturing Engineering)

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pitch yaw vibration measurements on rotors submitted.pdfAccepted version3.35 MBAdobe PDFView/Open
pitch yaw vibration measurements on rotors submitted.pdfSubmitted version3.04 MBAdobe PDFView/Open

 

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