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In the process of aircraft residual ice detection based on near infrared spectrum method, the qualities of the images, such as brightness and contrast, are easily influenced by sunlight, weather and other factors. Therefore, it is hard to precisely match the feature points. In this paper, an improved Harris local invariant feature matching method is proposed. The improved Harris feature point detection...
To realize automatic flaw classification of an ultrasonic phased array system, the key is to extract flaw feature that can mostly represent flaw's nature from ultrasonic signals. As ultrasonic echoes are nonstationary signals, wavelet packet transform (WPT) is a common feature extraction method. But it is fit for off-line signal analysis. In this article, lifted wavelet transform (LWT) is studied...
Layer detection method is applied in flaw detection of pipeline girth welds when ultrasonic is used. As every layer must be detected, the detection location is changed continuously. The focal length of traditional ultrasonic transducer is fixed. When tested location is changed, the transducer has to be changed, reducing the detection efficiency. Ultrasonic phased array transducer has the ability of...
Presently, flaw classification of ultrasonic phased array systems is completely manual. It is dependent on the operator's testing experiences and errors are very easily introduced. In this article, "energy-status" method based on wavelet packet transform, having time-frequency signal analysis character, is applied to achieve ultrasonic echo signals' feature. Then, a feature library is built...
Traditional ultrasonic testing system has fixed focus, which is burdensome for layer inspection of welds because different layer needs different steering angle and focus ultrasonic beam to inspect. Ultrasonic phased array testing instrument can electronically steer and focus the transmission ultrasonic beams. This ability makes it very advantageous in automatic nondestructive testing in industrial...
An automatic ultrasonic phased array inspection system used for nondestructive testing (NDT) of pipeline girth weld is developed. The linear phased array transducer is optimized by numerical analysis based on a mathematical model. Then hardware and software designs of the system are presented, realizing dynamically focusing in the detection area. A series of technological difficulties are solved....
Ultrasonic phased array technology is a promising industrial nondestructive testing (NDT) method for its excellent abilities of electronic steering, deflection and focusing. Nowadays, the ultrasonic phased array systems can locate the detected flaw, but flaw classification is still determined by the inspection operator. Therefore, human errors are unavoidable. This article proposes a fractal-based...
As flaw classification is normally manual determination in ultrasonic nondestructive testing field, an automatic identification of flaw type based on Lifted Wavelet Transform (LWT) and BP neural network (BPN) is introduced in this paper. LWT is proposed to extract flaw feature from ultrasonic echo signals, ideally matched local characteristics of original signals. The computational speed and flaw...
Based on electronic deflection and focusing characteristics, ultrasonic phased array technology is used in flaw detection of girth welds for big diameter long distance pipelines, which overcomes the shortcomings in traditional ultrasonic nondestructive testing. Aimed at the detection requirements, a numerical analysis and modelling of a linear phased array transducer are carried out in this article...
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