Research On Structural Damage Detection By Hilbert-Huang Transform

Structural damage detection can help to fully understand the state of structural damage and the changes of the carrying capacity. It's of great significant for disaster prevention and reduction.This paper summarized the development and the current situation of the structual damage detection, put emphasis on the application review of Hilbert-Huang Transform (HHT) in damage detection. On the basis of previous accomplishment, the paper aimed at the requirement of structual damage detection, took full advantage of adaptivity and capability of HHT, and widened this new signal processing method from time domain to spatial domain, from one-dimensional to two-dimensional to use it in structural damage detection.The paper introduced the basic theory and method of HHT in detail, summarized the algorithm of Empirical Mode Decomposition (EMD), clarified the the physical significance of Hilbert spectrum analysis, discussed some problems of EMD, such as the ending effect, orthogonality and completeness, frequency resolution ect., and programmed the corresponding algorithm.According to the definition and characteristics of signal singularity,the paper analysed the theory of signal singularity detection by HHT, introduced the EEMD method to HHT, made use of its improvement on mode mixing, enabled it to become a effective tool for signal singularity detection by decomposition in time domain and transform in frequency domain, applied the method to ASCE's benchmark Structural Health Monitoring problems, identified the time, location and degree of damage.The paper also derived the modal shape changes of damaged Euler-Bernoulli beam and thin plate, put forward special 1-D and 2-D HHT method, utilized mode singularity caused by damage, advanced relevant damage index, detected the location and degree of damaged beam and plate, validated the method effectivity by modal test, discussed the relationship of damage index and damage degree under different modal.For crack detection, the paper established cracked cantilever beam equivalent SDOF model and finite element model with contact pair, analysed the nonlinear characteristics of response when crack is open and close under free and forced vibration, used HHT method to separate the nonlinear signal which represent damage and the response signal which caused by excitation frequency, described this nonlinear characteristics well and truly via the changes of instantaneous frequency.