Abstract
Cepstral methods of modal analysis offer two advantages with respect to conventional methods. The first is that they give both poles and zeros of the transfer function, and thus most of the information about the relative scaling of the residues of adjacent modes. Fully scaled modes can be obtained using a minimum of extraneous information, which can be provided for example by a finite element (FE) model of the structure, which does not have to be very accurate. The other advantage is that for single input, multiple output (SIMO) systems, the cepstrum of the responses is the sum of the cepstra of the forcing and transfer functions, and provided the spectrum of the force is reasonably smooth (on a log scale) the corresponding cepstrum is very short and the higher quefrency part of the cepstrum is completely dominated by the transfer function and can be curve-fitted for its poles and zeros. This is a much weaker restriction than the assumption of most techniques that the excitation is white. The above properties of the cepstrum apply only to SIMO systems and in the normal MIMO situation one possibility is to separate the responses to a single input at each measurement point. The methods available for this include blind source separation (BSS) techniques, for convolutively mixed systems. An exciting possibility is where there is just one second order cyclostationary source with a particular cyclic frequency such as with a diesel railcar. The responses to this single source can be separated in the cepstrum of the spectral correlation function. A very recent development is the possibility of performing editing of time signals using the real cepstrum instead of the complex cepstrum. The latter contains all information about the phase, but only if it can be unwrapped to a continuous function of frequency, and this is not possible for stationary forcing or response functions. For many applications, the original phase can be combined with the edited amplitude information from the real cepstrum, even for general stationary responses.
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References
Bogert BP, Healy MJR, Tukey JW (1963) The quefrency alanysis of time series for echoes: cepstrum, pseudo-autocovariance, cross-cepstrum, and saphe cracking. In: Rosenblatt M (ed) Proceedings of the symposium on time series analysis, Wiley, pp 209–243
Childers DG, Skinner DP, Kemerait RC (1977) The cepstrum: a guide to processing. Proc IEEE 65(10):1428–1443
Oppenheim AV, Schafer RW (1989) Discrete time signal processing. Prentice-Hall, New Jersey
Polydoros A, Fam AT (1981) The differential cepstrum: definitions and properties. In: Proceedings of the IEEE international symposium on circuits systems, Chicago, pp 77–80
Antoni J, Guillet F, Danière J (2000) Identification of non-minimum phase transfer functions from output-only measurements. In: ISMA25 conference, KUL, Leuven
Ibrahim SR (1984) A modal identification algorithm for higher accuracy requirements. In: AIAA proceedings of the 25th structures, structural dynamics and materials conference paper 84–098, pp 117–122
Gao Y, Randall RB (1996) Determination of frequency response functions from response measurements. Part I: extraction of poles and zeros from response cepstra. Mech Syst Signal Process 10(3):293–317
Gao Y, Randall RB (1996) Determination of frequency response functions from response measurements. Part II: regeneration of frequency response functions from poles and zeros. Mech Syst Signal Process 10(3):319–340
Antoni J, Braun S (eds) (2005) Special issue: blind source separation. Mech Syst Signal Process 19(6): 1163–1380
Hanson D (2006) Operational modal analysis and model updating with a cyclostationary input. Ph.D. Thesis, UNSW, Sydney. Available through UNSW Library. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-UN20070508.134919/index.html
Hanson D, Randall RB, Antoni J, Thompson DJ, Waters TP, Ford RAJ (2007) Cyclostationarity and the cepstrum for operational modal analysis of mimo systems—part I: modal parameter identification. Mech Syst Signal Process 21(6):2441–2458
Hanson D, Randall RB, Antoni J, Thompson DJ, Waters TP, Ford RAJ (2007) Cyclostationarity and the cepstrum for operational modal analysis of mimo systems— part II: obtaining scaled mode shapes through finite element model updating. Mech Syst Signal Process 21(6):2459–2473
Randall RB (2001) Cepstrum analysis. In: Ewins D, Rao SS, Braun S (eds) Encyclopedia of vibration. Academic, London
Randall RB, Sawalhi N (2011) Use of the cepstrum to remove selected discrete frequency components from a time signal. In: IMAC XXIX, Jacksonville
Randall RB (2009) Cepstral methods of operational modal analysis, Chap 45. In: Encyclopedia of structural health monitoring, Wiley, Chichester, UK
Acknowledgements
This research was partly supported by the Defence Science and Technology Organisation (DSTO) through the Centre of Expertise in Helicopter Structures and Diagnostics at UNSW.
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© 2012 The Society for Experimental Mechanics, Inc. 2012
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Randall, R.B. (2012). Updated Cepstral Methods for Operational Modal Analysis. In: Allemang, R., De Clerck, J., Niezrecki, C., Blough, J. (eds) Topics in Modal Analysis I, Volume 5. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-2425-3_18
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