Research On Compressive Sampling And Damage Identification For Structural Health Monitoring Based On Phased Array

At the beginning of the damage to the structure, smart structural health monitoring can monitor the condition of structural online in real time, and recognize the damage in the structure exactly by using sensor technology and the advanced method for signal processing. It can reduce catastrophic accidents and ensure the safety of engineering. Ultrasonic phrased array technology can bring about the deflection, focusing and other effects by adjusting the time delay of launching and receiving the signal of each element. Compared with traditional ultrasonic monitoring technology, ultrasonic phrased array technology can scan comprehensively and in multi-angle without moving the probe, which can improve the monitoring accuracy.The thesis discusses the correlative theory of phased array healthy monitoring, explaining the advantage superiority for the phased array monitoring technology. It takes eight elements of the ultrasonic phrased array technology, which monitors the aluminum material.By controlling the time delay of launching and receiving of piezoelectric array elements, it completes acoustic beam scanning in multi-direction, which combines many signal process ways to manage received phrased array signals and gain the position of the damage to show in the image.In signal collection process, power frequency interference signal will be mixed inevitably. Combine with Butterworth filtering method, Chebyshev filtering method and elliptic filtering method to process signals in advance. In Matlab signal process tool, call digital filter to simulate the filtering effect in order to achieve more exact signal.During the process of damage identification, the thesis designs effective phrased array monitoring system to collect signals. According to the formula and analysis of algorithm, delaying time of launching and receiving process will be achieved. Then the amplitude of combining signals should be normalization managed, the grayscale of the image is expressed by the amplitude of according damage signal, therefore the brightest represents the damage.The signals received from ultrasonic phrased array technology also contain a large amount of noisy signals. Because the damage image got from original data is not perfect, combined with image enhancement method to process it, and then the image can be more clearly. The process of traditional image enhancement exists shortcomings in contrast decreasing and noise amplification, which leads to detail information of the images missing. In order to overcome those shortcomings and get intensified images with an impressive effect, the thesis applies fuzzy sets methods to it.During the process of traditional sample collection, Nyquist sampling theorem is followed. Ultrasonic phased array technology collects more information, which makes difficult for signal to store and to transmit. The thesis takes compressed sensing technology to deal with ultrasonic signal, which reduces the amount of information for store and transmission immensely. Main functions include:(1) Compressed sensing is a handling method on the basis of sparse signals and it converts non-sparse ultrasonic signal to the sparse signal by using sparse transformation matrix. (2) Design the measurement matrix to gain sparse vector matrix. (3) Take various reconstruction algorithms for compressed sensing to restructure original signals. Compared errors of the reconstruction, choose the best reconstruction algorithms to complete the test. Eventually use compressed sensing manage signals to determine the position of damage.