Structural Modal Parameter Identification And Damage Analysis Based On Vibration Signal

Modal parameter identification of vibration is required by structural vibration characteristics analysis, damage diagnosis, and optimization design of structural dynamics characteristics. This paper is based on the application of wavelet analysis and Hilbert-Huang transform in structural modal parameter identification, and the structural damage is also analyzed.1. The modal parameter identification of structural vibration by Morlet wavelet transform is studied. The free vibration response signal is analyzed by Morlet wavelet transform. The instantaneous frequency and amplitude are recognized by the scale and the wavelet coefficient of the ridge, so the inherence frequency and damping ratios are estimated. The signal of free vibration response is analyzed between 2 and 20 of wavelet factor N by the relation of wavelet factor and wavelet center frequency. If wavelet factor N is larger, it will be better in Modal parameter identification. But it is instead of reducing the resolution in time. The parameter of N is applied to solve the contradiction of resolution between in time and in frequency making both of them better. Modal parameter identification of vibration in noisy environment based on correlation function is researched. For identification the vibration signal which is added white noise signal, the method is proposed, which is based on the theory that the wavelet transform coefficient of noise signal is very small and the main vibration signal is low-frequency signal. The identification error is controlled in permitted range.2. Modal parameter identification of vibration based on EMD is researched. And the identification error is less in five percent. For three degree of freedom structure, the method of HHT is bad. The signal based on band pass filter before it is processed by HHT. And the identification error is also small using this method. The method based on the combing of Morlet wavelet and EMD is proposed for parameter identification. The vibration signal which is decomposed by EMD is transformed by wavelet. The identification error is controlled in eight percent. The noised signal of structural vibration is analyzed. For identification the vibration signal which is added white noise signal, the method of HHT is proposed. The identification error is bigger for the bad decomposed by EMD.3. Structural damage is studied by the methods of Modal parameter identification and wavelet energy. The former is based on the change of Modal parameter in the damaged structure. For the ratio of attenuation factor may be large in the structural, multiplied by the smallest inverse index method is proposed in the damaged modal. The latter is based on change of the signal energy in each band frequency in damaged modal, which is decomposed by the wavelet packet.