Abstract
The response of a linear time-invariant (LTI) system to harmonic input generates a harmonic output with constant frequency but varying magnitude and phase. Many structural dynamic systems have been modeled as linear time-varying periodic (LTP) systems. Previous studies have reported that the response of an LTP system to an exponential input establishes an infinite number of frequencies. These studies have presented a new, exponentially modulated periodic signal space and a corresponding harmonic transfer function as useful tools in the operational modal analysis of LTP systems. In consideration of this new approach, this study mainly identifies the frequencies of a typical LTP system, such as a beam that is subject to the intermittent passage of moving masses. Upon obtaining the harmonic transfer function for the beam-moving mass system, conventional frequency domain methods for LTI systems are used to derive the frequency characteristics of the LTP system from the system response. These methods include the peak-picking method. As expected in an LTP system, an infinite number of pseudo-natural frequencies resonate in the beam-moving mass system.
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Esmaeil Ghorbani was born in Iran in 1986. He received his B.S. degree in mechanical engineering from the University of Mazandaran in 2009 and his M.S. degree in mechanical engineering from Isfahan University of Technology, Isfahan, Iran in 2012. His research interests include experimental and operational modal analysis, condition monitoring and fault diagnosis using vibration data, and gas turbines. He works as a project manager in the design and construction of HRSG (Heat recovery steam generator) boilers in Iran.
Mehdi Keshmiri was born in Iran, Iran in 1961. He received his B.S. and M.S. degrees in mechanical engineering from Sharif University of Technology, Tehran, Iran, in 1986 and 1989, respectively. He finished his Ph.D. in mechanical engineering at McGill University, Montreal, Canada. He is currently an associate professor in the Department of Mechanical Engineering of Isfahan University of Technology (IUT), Isfahan, Iran. His research mainly focuses on system dynamics, control systems and dynamics, and the control of robotic systems. He has presented and published more than 100 papers in international conferences and journals and supervised more than 60 graduate students.
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Ghorbani, E., Keshmiri, M. Identification of pseudo-natural frequencies in a beam-moving mass system with periodic passages. J Mech Sci Technol 29, 2729–2734 (2015). https://doi.org/10.1007/s12206-015-0601-4
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DOI: https://doi.org/10.1007/s12206-015-0601-4