Damage Detection Based On Wavelet Analysis And Pipeline Applications

Wavelet transformation is a time-scale and time-frequency signal analysis. It has many desirable properties, and has been widely applied in many fields.In this thesis, the theory of wavelet transform and the knowledge of pressure pipe are given. The theory of wavelet transform is introduced into area of damage detection, and one method for damage detection and two methods for detection of simple- supported beam are proposed. And apply the theory into the experiment of pressure pipe line.The main work of this thesis includes three aspects:(1) A equation of hard threshold wavelet de-noise is reasoned out. Through the equation, free response can be gotten from random response. Using the principle of time-frequency analysis based on orthonormal discrete wavelet transformation, it can detect damage by analyzing how the frequency content of observation signal changes with time.(2) A wavelet-based approach is proposed for damage identification in beam structure. The displacement of the damaged simple-supported beam under sudden force is analyzed using continuous wavelet transform and the location is estimated by the maximum of wavelet coefficients. Also the displacement is analyzed by wavelet packet and the extent of the damage is estimated by the energy index. And then, the real-time structural damage detection technology is studied based on wavelet packet analysis. The method is applied to detect simple-supported beam cracks.(3) The paper use the method of frequency change square ratio, the theory of wavelet and the related program to detect the damage of a pipe. And with the experiment, the result is good, the methods are effectual.