Nonlinear Structural Identification Based On Hilbert-Huang Transform

Many lifeline critical and infrastructure projects are currently under construction in China due to the rapid development of China’s economy. Under the combined effects of long-term loading, fatigue and other factors, catastrophic incidents appear more commonly. Therefore, the structural health status detection and the assessment of structural safety, reliability, serviceability and durability, has become a hot issue in the field of civil engineering, disaster prevention and mitigation. Structural parameter identification is one of the most critical aspects in structural health monitoring with a very important theoretical and practical significance. This dissertation introduces the Hilbert-Huang Transform method. HHT is an adaptive and efficient method for handling of non-linear and non-stationary data. This dissertation attempts to deal with non-linear properties demonstrated by structures with HHT.The Hilbert transform in the second part along with the empirical mode decomposition and the ensemble empirical mode decomposition. The intriguing issues of the signal envelope computation are discussed. The advantages and disadvantages of various envelope processing methods are demonstrated with examples.The non-linear categories and the corresponding engineering examples are presented in the third part. Based on traditional linear vibration theory, the inverse Fourier transform of the frequency response function of a structure is a signal having a causal relationship with the frequency response function itself. The criterion to determine whether a structure is falling in the nonlinear state using Hilbert Transform is derived in this part. The difference between the amplitudes of structural frequency response function and its Hilbert transform is found to be a measure of structural nonlinear degree. First, a single degree of freedom vibration system under seismic excitation is used to verify the effectiveness of the method. Then, linear and nonlinear experimental data with white noise excitation are processed and analyzed separately. Comparative results showed the effectiveness of the method.The parameters of time-varying damping system and nonlinear vibration system such as Duffing vibration system and Van der Pol vibration system are identified by Hilbert-Huang transform in the fourth part of the dissertation. Firstly, the vibration signal is separated into free vibration and forced vibration signal by the empirical mode decomposition. Then, the amplitude envelope and the instantaneous frequency of the signal is obtained by empirical envelop method. Secondly, the parameters are identified used the amplitude envelope and the instantaneous frequency of the signal by the least square method. The parameters identification method of time-varying damping systems and nonlinear vibration systems based on HHT is proved to be effective by numerical examples. Compared with the results of wavelet analysis method, the advantages of HHT method are demonstrated.