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Detection and Frequency Estimation of Nonlinear Systems using Step Relaxation Technique

Sabesan, Vaidhyanathan
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1505203318448279

Abstract Details

2017, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
This thesis deals with detection and analysis of nonlinearity in a physical MDOF system. One of the ways to characterize the non-linearity present in the system is to track the variation of frequency with time. The first part of the thesis deals with the excitation of the system. Two types of excitations are considered in this thesis: Shaker excitation and step relaxation. The results from both excitations are compared. The second part of the thesis deals with the analysis of the measured data and estimation of the variation of natural frequency in the system. A plot of frequency variation with amplitude from a shaker excitation is relatively straight forward whereas, the data generated from step relaxation needs the usage of time varying frequency estimation methods. Various commonly used methods for detecting time varying frequency are implemented – Least squares method, Short Time Fourier Transform (STFT), Wavelets and Hilbert transform. The pros and cons of each of these methods are discussed in Sections 2 and 4. A new method for frequency estimation from wavelets and STFT is implemented. The current research focuses on analysis methods to be used specifically for SDOF systems, whereas all practical systems are MDOF, containing more than 1 frequency in the range of consideration. Thus, the ability of analyzing MDOF data for each of the methods is evaluated. A common limitation in the usage of wavelets is the decrease in frequency resolution with increase in frequency of the signal. The creation of `artificial aliasing’ is proposed to counteract this effect. The experimental data obtained for a clearance non-linearity and a stiffness non-linearity are used to generate the results.
Randall Allemang, Ph.D. (Committee Chair)
Allyn Phillips, Ph.D. (Committee Member)
David Thompson, Ph.D. (Committee Member)
82 p.
Mechanical Engineering
wavelet; nonlinear; vibration; transient; time varying; detection

Recommended Citations

Citations

  • Sabesan, V. (2017). Detection and Frequency Estimation of Nonlinear Systems using Step Relaxation Technique [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1505203318448279

    APA Style (7th edition)

  • Sabesan, Vaidhyanathan. Detection and Frequency Estimation of Nonlinear Systems using Step Relaxation Technique. 2017. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1505203318448279.

    MLA Style (8th edition)

  • Sabesan, Vaidhyanathan. "Detection and Frequency Estimation of Nonlinear Systems using Step Relaxation Technique." Master's thesis, University of Cincinnati, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1505203318448279

    Chicago Manual of Style (17th edition)

ucin1505203318448279
449
© 2017, some rights reserved.Creative Commons License Detection and Frequency Estimation of Nonlinear Systems using Step Relaxation Technique by Vaidhyanathan Sabesan is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.