Structural Condition Monitoring by Cumulative Harmonic Analysis of Random Vibration

Figure 3

Examples of CHA and spectrograms for random record of single-degree-of-freedom (SDOF) system. (a) CHA magnitude and (b) spectrogram using STFT conditions are frame length, that is, 0.18 with zero padding under conditions where total Fourier-transform length is 91 and frame hop size is 1/10 frame length. Time intervals are normalized by impulse response record length (1000 points). (c) Moving averaged spectrogram using averaging STFT, (b) frame-by-frame, (d) random record to be analyzed, and (e) impulse response record of vibration system where length is defined by reverberation time. (f) Magnitude response and normalized frequency, (g) close up of CHA magnitude in (a) at final observation instant accumulation time of 1, and (h) pole plot of transfer function for impulse response in (e).