Damage Identification Research Of Plate-Like Structures By Means Of The Two-dimensional Wavelet Analysis

The elastic plate is a common structure in civil engineering. However, there may be a variety of damages during construction. When the damages accumulate to a certain extent, it will affect the safety of the structure, and even, result in serious catastrophic accidents that endanger the lives of people and cause heavy financial losses to the society. Therefore, how to effectively identify the damages of elastic plates is of great importance.Wavelet analysis has been an international research frontier over the last decade, and it is considered to be a breakthrough in the development of Fourier analysis and a new two-dimension time-frequency analytical method. The method of wavelet analysis has the property of spatial localization, that is, the wavelets changes of signals at a specific point are determined completely by the information from the vicinity of the point. It has unique advantages in the area of singularity detection. Therefore, it has not only great theoretical significance but also a certain application value in engineering to employ the two-dimension wavelet analysis method to study structure damage identification problems.The wavelet analysis theory is introduced in this paper. This paper also analyzes the dynamic characteristics of the plates and the influences of local plate damages on the dynamic characteristics of the structure. And then this paper also carries on a more systematic study on the plate damage identification methods based on the vibration mode and the corner of two-dimension wavelet transform. The researching objects are respective:four edges simply supported plates, plates fixed at four sides, and plates clamped and stiffened at both ends. The Lanczos Method is employed to do modal frequency analysis, calculate the vibration mode and corner mode, do two-dimension wavelet transform for the feature quantities of the damage information, establish the damage detection mechanism of the damaged plate structure according to the wavelet singularity detection theory, and discuss modal parameters damage identification method.The approach to identify plates'damages is established based on the vibration mode two-dimension wavelet transform. This approach takes the db wavelets as mother wavelets, and carries on two-dimension wavelet transformation for the damaged plates. It identifies the damage position by the maxima modulus of wavelet coefficients in the multi-scale analysis and determines the damage extent by the size of the maxima modulus. By calculating and analyzing damaged plates (including the four edges simply supported plates, plates fixed at four sides, and plates clamped and stiffened at both ends), the effectiveness of this approach is verified. The signal extension theory is applied in the process of the damage identification to perform the signal extension for the modal parameters of the damaged plates. Then the two-dimension wavelet transformation is carried on to effectively remove the influences of the boundaries on the damage detection.The paper, for the first time, puts forward the damage detection method based on the vibration mode and the corner of two-dimension wavelet transform. This method takes the Mexh as the mother wavelets, and carries on two-dimension wavelet transformation for the damaged plates. It identifies the damage position by the maxima modulus of wavelet coefficients in the multi-scale analysis and determines the damage extent by the size of the maxima modulus. By calculating and analyzing damaged plates (including the four edges simply supported plates, plates fixed at four sides, and plates clamped and stiffened at both ends), the effectiveness of this approach is verified. Comparing with the approach based on the vibration mode tow-dimension wavelet analysis, it is found that this method is more smooth wavelet coefficients and more singularity effective in identifying plates damages and more accurate in reflecting the damaged position and extent. Combined with the limited unit method, this method has reference value in plates'damage identification in the engineering application.