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Type of Document	Dissertation
Author	Bradford, Samuel Case
URN	etd-11292006-214839
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-11292006-214839
Title	Time-frequency analysis of systems with changing dynamic properties
Degree	PhD
Option	Civil Engineering
Advisory Committee	Advisor Name Title John F. Hall Committee Chair J.L. Beck Committee Member Monica D. Kohler Committee Member Robert W. Clayton Committee Member Thomas H. Heaton Committee Member
Keywords	structural health monitoring Wigner-Ville Distribution damage detection wavelets spectrogram Millikan Library
Date of Defense	2006-07-19
Availability	unrestricted
Abstract The Wigner-Ville Distribution, and related refinements, represent a class of advanced time-frequency analysis tools that are distinguished from Fourier and wavelet methods by an increase in resolution in the time frequency plane. Time-frequency analysis provides a set of exploratory tools for analyzing changing frequency content in a signal, which can then be correlated with damage patterns in a structure. For systems of interest to engineers, investigating the changing properties of a system is typically performed by analyzing vibration data from the system, rather than direct inspection of each component. Nonlinear elastic behavior in the force-displacement relationship can decrease the apparent natural frequencies of the system - these changes typically occur over fractions of a second in moderate to strong excitation and the system gradually recovers to pre-event levels. Structures can also suffer permanent damage (e.g., plastic deformation or fracture), permanently decreasing the observed natural frequencies as the system loses stiffness. Advanced time-frequency representations provide a set of exploratory tools for analyzing changing frequency content in a signal, which can then be correlated with damage patterns in a structure. Modern building instrumentation allows for an unprecedented investigation into the changing dynamic properties of structures: a framework for using time-frequency analysis methods for instantaneous system identification is discussed.
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