Hostname: page-component-78c5997874-j824f Total loading time: 0 Render date: 2024-11-10T15:22:20.352Z Has data issue: false hasContentIssue false
  • English
  • Français

Harmonic and modal frequency discrimination in time domainoperational modal analysis

Published online by Cambridge University Press:  06 February 2014

V.H. Vu ,
M. Thomas  and
F. Lafleur
V.H. Vu
Affiliation:
École de Technologie Supérieure, 1100 Notre Dame West, Montréal, Qc, H3C 1K3, Canada
M. Thomas*
Affiliation:
École de Technologie Supérieure, 1100 Notre Dame West, Montréal, Qc, H3C 1K3, Canada
F. Lafleur
Affiliation:
Institut de recherche d’Hydro Québec, 1800 Bl. Lionel-Boulet, Varennes, J3X 1S1, Canada
*
a Corresponding author: marc.thomas@etsmtl.ca
Get access

Abstract

An algorithm of operational modal analysis in time domain is presented for thediscrimination between structural modes, harmonic excitations and spurious modes. Aclassification factor is developed and based on the construction of the damped signal- to-noise ratio which separates the physical modes from the numerical ones. The harmonicexcitations are then recognized at very high power indexes and zero damping. Furthermore, after the modal discrimination, the harmonic spectrum and the estimated frequency responsefunction can be derived. The method can be updated in the time domain either by a shorttime sliding window or a recursive technique to provide the modal monitoring in bothstationary and non-stationary process. An industrial application on a hydro-electricalgenerator is discussed to identify the machine frequencies under operational workingconditions.

Keywords

Modal identificationmode separationrecursive analysisshort-time modelingnon-stationary vibrationhydro-electric generator
Type
Research Article
Information
Mechanics & Industry , Volume 15 , Issue 1 , 2014 , pp. 29 - 37
Copyright
© AFM, EDP Sciences 2014

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

R. Brincker, P. Andersen, N. Møller, An Indicator for Separation of Structural and Harmonic Modes in Output-Only modal Testing, IMAC XVIII, 2000, 8p
N.J. Jacobsen, Eliminating the Influence of Harmonic Components in Operational Modal Analysis, IMAC XXV, 2007, 11 p
D.L. Brown, R.J. Allemang, R. Zimmerman, M. Mergeay, Parameter Estimation Techniques for Modal Analysis, 7th International Seminar on Modal Analysis, Katholieke Universiteit Leuven, Belgium, 1985
Ibrahim, S.R., Mikulcik, E.C., A method for Direct Identification of Vibration Parameters from the Free Response, The Shock and Vibration Bulletin 47 (1977) 183−198 Google Scholar
Mohanty, P., Rixen, D.J., Operational modal analysis in the presence of harmonic excitation, J. Sound Vib. 270 (2004) 93−109 CrossRefGoogle Scholar
Vu, V.H.., Thomas, M.., Lakis, A.A.., Marcouiller, L.., Operational modal analysis by updating autoregressive model, Mechanical systems and signal processing (MSSP), Elsevier, 25 (2011) 1028−1044 Google Scholar
Vu, V.H., Thomas, M., Lafleur, F., Marcouiller, L.., Towards an automatic spectral and modal identification from operational modal analysis. J. Sound Vib. Elsevier. 332 (2013) 213−227 CrossRefGoogle Scholar
S.M. Pandit, 1991, Modal and spectrum analysis: data dependent systems in state space. New York, J. Wiley and Sons, 415 p.
F. Lafleur, V.H. Vu, M. Thomas, Oct 2011, Case study of operational modal analysis of a large hydroelectric generator, Proceedings of the 29th Seminar on machinery vibration, Canadian Machinery Vibration Association, St John (NB, Canada), 11 pages
V.H. Vu, M. Thomas, F. Lafleur, Oct 2011, Operational Modal Monitoring of High Power Hydro-electrical Generators. Proceedings of Surveillance 6, Compiègne, paper 5. 12 p.
V.H. Vu, M. Thomas, F. Lafleur, May 2011, Operational Modal Monitoring of High Power Hydro-electrical Generators, Proceedings of IOMAC, Istanbul, paper 410 8 p
V.H. Vu, M. Thomas, A.A. Lakis, L. Marcouiller, Short-Time Autoregressive (STAR) Modeling for Operational Modal Analysis of Non-stationary Vibration. Chapter 3 on book: Vibration and structural acoustic analysis, Springer, 2011, pp. 59−77
Vu V.H., M. Thomas, A.A. Lakis and L. Marcouiller, 2010, On line Time-Modal monitoring of non stationary systems, Revue Internationale sur l’Ingénierie des Risques Industriels (JI-IRI), 3, pp. 45−65
V.H. Vu, M. Thomas, 28 Août 2013, Uncertainties on Modal Parameters by Operational Modal Analysis, Congrès Français de la Mécanique, Bordeaux, 6 p