Extracting instantaneous phase features for structural health monitoring
A general time-frequency data analysis method, the Empirical Mode Decomposition (EMD) and Hubert Spectrum, in conjunction with a wave-mechanics-based methodology is developed for structural health monitoring. Sets of simple basis function components, known as Intrinsic Mode Functions (IMF), are extracted adaptively from the measured structural response time series. These MFs are amplitude and phase modulated signals, and can be used to define time-dependent amplitudes, phases, and frequencies for modeling nonlinear and non-stationary processes. Damage features are extracted based on a fundamental relationship connecting the instantaneous phases of a measured time series to the structural mass and stiffness parameters. Damage detection applications are investigated for various degrees of preload loss in a bolted connection between a composite beam and steel plates. The beam is excited by a low dimensional deterministic chaotic force. The time series output at a variety of locations on the beam and plate are then analyzed with the method. The time-frequency features and instantaneous phase relationships are extracted and examined for changes which may occur due to damage. These results are compared to results from other newly developed detection algorithms based on the geometric properties of a chaotic attractor.
