Modal parameter identification using the log decrement method and band-pass filters

• Published in: Journal of sound and vibration Vol. 330; no. 21; pp. 5014 - 5023
• Main Authors: Liao, Yabin, Wells, Valana
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 10-10-2011; Elsevier
• Subjects: Bandpass filters; Damping; Exact sciences and technology; Frequency ranges; Fundamental areas of phenomenology (including applications); Least squares method; Measurement and testing methods; Parameter identification; Physics; Polymethyl methacrylates; Solid mechanics; Sound; Structural and continuum mechanics; Vibration; Measurement; Parameter estimation; Modal analysis; Methyl methacrylate polymer; Vibration test; Experimental study; Test bar; Dynamic test; Vibration damping; Time domain method; Least squares method; Band pass filter; System identification
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/j.jsv.2011.05.017

This paper presents a time-domain technique for identifying modal parameters of test specimens based on the log-decrement method. For lightly damped multidegree-of-freedom or continuous systems, the conventional method is usually restricted to identification of fundamental-mode parameters only. Implementation of band-pass filters makes it possible for the proposed technique to extract modal information of higher modes. The method has been applied to a polymethyl methacrylate (PMMA) beam for complex modulus identification in the frequency range 10–1100
Hz. Results compare well with those obtained using the Least Squares method, and with those previously published in literature. Then the accuracy of the proposed method has been further verified by experiments performed on a QuietSteel specimen with very low damping. The method is simple and fast. It can be used for a quick estimation of the modal parameters, or as a complementary approach for validation purposes.
► The paper presents a method to identify the modal frequencies and damping ratios of MDOF and continuous systems. ► The method applies the log decrement technique to frequency components isolated by band-pass filters. ► The method is simple to implement and its accuracy has been verified through simulations and experiments. ► The effects of the band-pass filtering, sampling, and measurement noise on the estimation accuracy are discussed.