Advanced Nondestructive Evaluation I

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Authors: Gi Young Park, C.K. Lee, Jung Taek Kim, K.C. Kwon, Sang J. Lee
Abstract: To monitor the wear and degradation on a pipe by corrosion during a plant operation, the vibration signals were measured by an accelerometer and analyzed by several analysis techniques. From the conventional methods, it was difficult to identify the wear and degradation on the pipe. And hence, the time-frequency distribution (TFD) and the adaptive cone-kernel distribution (ACKD) devised for reducing the interfering cross-terms are applied to the acquired data. They can provide the distinguishing peak patterns between the normal and corrosion signals.
Authors: Chung Hyo Kim, Tae Sik Kong, Young Jun Lee, Hee Dong Kim, Young Ho Ju
Abstract: H.264/AVC is adopted as a next generation moving picture compression standard. Context-based Adaptive Binary Arithmetic Coding (CABAC) is the major entropy coding algorithm employed in H.264/AVC. Although the performance gain of H.264/AVC is mostly resulted from CABAC, it is difficult to implement a high-throughput decoder due to its decoding complexity. Although CABAC excludes a multiplication, the algorithm is basically sequential and needs large computations to compute some important variables, which are range, offset and context variables. Therefore, it is difficult to achieve fast decoding performance. In this paper, a prediction scheme is proposed to decode maximally two bits at a time and thus to reduce overall decoding time. A CABAC decoder based on the proposed prediction scheme reduces total cycles by 24% compared to conventional decoders.
Authors: J. Kim, P. Ramuhalli, L. Udpa, S. Udpa
Abstract: A key requirement in most ultrasonic weld inspection systems is the ability for rapid automated analysis to identify the type of flaw. Incorporation of spatial correlation information from adjacent A-scans can improve performance of the analysis system. This paper describes two neural network based classification techniques that use correlation of adjacent A-scans. The first method relies on differences in individual A-scans to classify signals using a trained neural network, with a post-processing mechanism to incorporate spatial correlation information. The second technique transforms a group of spatially localized signals using a 2-dimensional transform, and principal component analysis is applied to the transform coefficients to generate a reduced dimensional feature vectors for classification. Results of applying the proposed techniques to data obtained from weld inspection are presented, and the performances of the two approaches are compared.
Authors: Ding Kang, Cao Dangdang, Li Weihua
Abstract: This paper proves that the energy centre of symmetric window function is the coordinate origin in discrete spectrum analysis. The correction formula of frequency, amplitude and phase can be obtained using this character. Simulation demonstrates that this method can correct averaged power spectrum directly with simple algorithm and fast processing speed, and the interference of negative or narrow interval frequencies has little influence on correction precision. This method is suitable for all kinds of symmetric window. But it is not suited with dense frequencies signal or continuous spectrum.
Authors: Jin Ho Park, Yang Hann Kim
Abstract: A technique to localize an impact source for an elastic spherical shell is proposed. The conventional source localization techniques when the source is located on a dispersive medium, require both the time-of-arrival differences (TOADs) between the transducer signals and the group velocities. In practice, the material properties or the geometry of the medium are not fully informed, therefore the group velocity is not available. Furthermore, they are only applicable if we have a high signal-to-noise ratio (SNR). In this paper, we propose a method that can be applicable in practice, which does not need to know the group velocity, when we have a relatively small SNR. The scanning procedure over the structure to acquire a minimum variance point of the estimated group velocities is suggested. To reduce the noise effect, an exponential function is asymmetrically weighted in smoothed Wigner-Ville distributions (WVDs). Experiments have been conducted to confirm the validity of this method. As a result, the proposed technique is found to be effective for an impact source localization for a spherical shell without prior information on the group velocity, even in a noisy environment.
Authors: Eisaku Umezaki, Yuuma Shinoda, Katsunori Futase
Abstract: The behavior of liquid in containers subjected to impact loads due to free fall was investigated using a visualization technique. Two types of containers were used. One consisted of a case made of transparent plastic plates and a liquid-packing bag made of transparent plastic films. The bag contained about 1,000 ml of liquid. The other was a case made only of transparent plastic plates. The case contained about 1,000 ml of water. The liquid consisted of water and ethanol. Polyethylene particles of about 3 mm in diameter were included in the liquid to visualize the movement of liquid in the containers. The containers were subjected to impact due to free fall, and photographs of the containers were taken using a high-speed camera. Results indicated that the behavior of liquid in the container with a liquid-packing bag is different from that of the container without a liquid-packing bag.
Authors: Pichet Pinit, Tobita Susumu, Eisaku Umezaki
Abstract: A three-step phase shifting approach for automatic determination of the isoclinic parameter in photoelasticity is presented. Unreliable isoclinic values affected by the isochromatic parameter are solved using the white light. The method uses three fringe images digitally captured by a digital camera for three different configurations of the dark-field plane polariscope. For a circular disk under compression, results show the method permits the isoclinic parameter in the range -π/2 to π/2 with almost free of the isochromatic parameter and comparable with theory.
Authors: Yun Koo Chung, Ki Hong Kim
Abstract: Many visual automatic inspection methods are used in the assembly line of vehicles for improving quality and reducing a production cost. In order to resolve uneasy inspection problems, new useful methods and devices have been developed. A real factory environment has very poor optical conditions. Illuminations are affected by the sun lights passing through the windows of the factories. The floor is continuously vibrating, which could affect the posture of installed cameras and illumination devices. This paper describes how to overcome these problems and suggests the automatic inspection system applicable to the automobile assembly line. It introduces two feature extraction methods and algorithms to detect the opened car in the automobile assembly line. The methods for extracting these features are discussed in this paper with the experimental results.
Authors: Hyun Cho, Sung Jin Song, Hak Joon Kim, Hee Jong Lee, Sung Nam Choi
Abstract: Ultrasonic C-scan inspections have been used in various industrial fields. Usually, conventional ultrasonic C-scan systems have several mechanical manipulating axis controlled by a computer or an electronic device. These systems are suitable for the high resolution and inspection quality. But they are too heavy and bulky to carry in general, and many industrial fields do not require higher resolution than a hundred micron order. To take care of such a need, in this study we developed an ultrasonic C-scan system that does not have any mechanical manipulator to transport ultrasonic transducers. This system, named "M-Scanner", adopts an electro-magnetic position tracking sensor instead of mechanical manipulating axes in order to trace the transducer position. Furthermore, this new system is portable and has a reasonable construction cost along with practical inspection resolution required in many industrial field inspections.
Authors: Jong Wan Seo, Myung Chul Shin
Abstract: A color space used to create color on a computer monitor or a television screen is RGB color space. However, RGB color space is strongly related to each other, therefore RGB color space is inadequate for adjustment of brightness or contrast. Moreover RGB color space is not suitable for pattern recognition. For this reason, it is needed that color space conversion from RGB to YIQ, YUV or YCrCb. The color space conversion matrix consists of 3 by 3 matrix element that is represented by floating point numbers. However RGB or YUV color space is in integer domain. Therefore these transform lead to lose the least significant bit (LSB) of color space. We propose the simple and fast reversible transform matrix. No lose the least significant bit (LSB) and not required multiplication but shift and addition that provides for real time conversion of huge image.

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