Summarizing Results for Scaling OMA Mode Shapes by the OMAH Technique

Anders Brandt, Marta Berardengo, Stefano Manzoni, Marcello Vanali, Alfredo Cigada

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

Abstract

Methods for scaling mode shapes determined by operational modal analysis (OMA) have been extensively investigated in the last years. A recent addition to the range of methods for scaling OMA mode shapes is the so-called OMAH technique, which is based on exciting the structure by harmonic forces applied by an actuator. By applying harmonic forces in at least one degree-of-freedom (DOF), and measuring the response in at least one response DOF, while using at least as many frequencies as the number of mode shapes to be scaled, the mode shape scaling (modal mass) of all modes of interest may be determined. In previous publications on the method the authors have proven that the technique is easy and robust to apply to both small scale and large scale structures. Also, it has been shown that the technique is capable of scaling highly coupled modes by using an extended multiple reference formulation. The present paper summarizes the theory of the OMAH method and gives recommendations of how to implement the method for best results. It is pointed out, as has been shown in previous papers, that the accuracy of the mode scaling is increased by using more than one response DOF, and by selecting DOFs with high mode shape coefficients. To determine the harmonic force and responses, it is recommended to use the three-parameter sine fit method. It is shown that by using this method, the measurement time can be kept short by using high sampling frequency and bandpass filtering whereas spectrum based methods require long measurement times. This means that even for structures with low natural frequencies, the extra measurement time for scaling the mode shapes can be kept relatively short.
Original languageEnglish
Title of host publicationRotating Machinery, Vibro-Acoustics & Laser Vibrometry : Proceedings of the 36th IMAC, A Conference and Exposition on Structural Dynamics, 2018
EditorsDario Di Maio
Volume7
PublisherSpringer
Publication date2019
Pages1-8
ISBN (Print)978-3-319-74692-0
ISBN (Electronic)978-3-319-74693-7
DOIs
Publication statusPublished - 2019
Event36th Conference and Exposition on Structural Dynamics, 2018 - Rosen Plaza Hotel, Orlando, United States
Duration: 12. Feb 201815. Feb 2018

Conference

Conference36th Conference and Exposition on Structural Dynamics, 2018
LocationRosen Plaza Hotel
Country/TerritoryUnited States
CityOrlando
Period12/02/201815/02/2018

Keywords

  • Mode shape scaling
  • OMA
  • OMAH
  • Operational modal analysis
  • Sine excitation

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