• Korean Journal of Optics and Photonics
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• v.31 no.5
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• pp.205-212
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• 2020

In the performance of a wind turbine system, the blades play a vital role. However, they are susceptible to damage arising from complex and irregular loading (which may even cause catastrophic collapse), and they are expensive to maintain. Therefore, it is very important both to find defects after blade manufacturing is completed and to find damage after the blade is used for a certain period of time. This study provides a new perspective for the detection of internal defects in glass-fiber- and carbon-fiber-reinforced panels, which are used as the main materials in wind turbine blades. A gap or fracture between fiber-reinforced materials, which may occur during blade manufacturing or operation, is simulated by drilling a hole 5 mm in diameter in the middle layer of the laminated material. Then, a digital-image-correlation (DIC) method is used to detect internal defects in the blade. Tensile load is applied to the fabricated specimen using a tensile tester, and the generated changes are recorded and analyzed with the DIC system. In the glass-fiber-reinforced laminated specimen, internal defects were detected from a strain value of 5% until the end of the experiment, while in the case of the carbon-fiber-reinforced laminated specimen, internal defects were detected from 1% onward. It was proved using the DIC system that the defect was detected as a certain level of strain difference developed around the internal defects, according to the material properties.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.2
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• pp.65-72
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• 2012

A defect analysis program for a composite motor case was developed to apply the ultrasonic signal processing method, based on the ultrasonic pulse-echo method. With the proposed defect analysis program, defects of FRP delamination and FRP/Rubber disbond in the composite motor case could be quantitatively measured. The defects detected in the composite motor case were in good agreement with the results measured with the computed tomography and video microscope. This paper described the development process of the defect analysis program to convert the ultrasonic test data into the C-Scan images.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1256-1265
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• 1996

Soft-decision detectors are used in many FEC and ARQ schemes to enhance the bit-error-probability and system throughput. Also, the hybrid-ARQ protocol is a very efficient schemeto achieve overall performance improvement. In this paper, we propose a new hybrid-ARQ protocol based on the first-order Reed-Muller codes employing soft-decision detectors. The Reed-Muller codes have the virtue of being able to use the fast Green machine decoder that is simple to implement. As the performance measures, the bit-error-probability and system throughput are evaluted for the proposed hybrid-ARQ procol, and compared with those of other hybrid-ARQ schemes. It is shown that the use of the proposed hybrid-ARQ protocol results in significant performance improvement without causing much loss in view of system complexity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.123-124
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• 2011

• Composites Research
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• v.17 no.1
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• pp.47-54
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• 2004

Vacuum hot pressing has been used for the development of titanium metal matrix composites using foil-fiber-foil technique. Subsequent micro-mechanical characteristics of the composites are then investigated by means of several experimental methods. The levels of consolidation, together with mechanism based failure processes of the materials have been analyzed by employing a thermo-acoustic emission technique. As shown by the results, fiber strength degradation occurs during the consolidation, and particularly residual stresses results from the thermal expansion mismatch between fiber and matrix materials during cooling process are incorporated in the changes of mechanical properties of the finished products. In industrial applications, both qualitative and quantitative evaluations of the material-mechanical characteristics are particularly important, and therefore must be included in process development. The present paper represents a methodology by which this can be achieved.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.2085-2086
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• 2011

전력설비의 절연물이 사용 환경 영향을 받아 열화되어 방전이 발생하게 되는데, 이 때 발생하는 방전의 크기 및 량은 절연물의 결함 형태와 환경에 영향을 받아 다양하게 나타난다. 절연물 결함에서 발생하는 신호는 열, 전자파, 초음파, 빛의 형태이며, 이들 신호가 복합적으로 방출된다. 결함을 갖는 절연물 종류에 따라 발생하는 이상 신호 패턴을 분석하여 절연성능 저하를 검출할 수 있고, 절연성능 저하 원인 규명에도 활용된다. 본 연구에서는 전력설비에 사용하고 있는 결함 또는 열화된 애자류의 이상신호 발생의 근본원인을 고찰하였으며, 이들의 신호를 검출하는 적절한 방법을 제시하였다.

• Journal of Digital Convergence
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• v.14 no.11
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• pp.249-255
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• 2016

Since the elderly voices include a lot of noise caused by physiological changes in respiration, phonation, and resonance, the performance of the convergence health-care equipments such as speech recognition, synthesis, analysis program done by elderly voice is deteriorated. Therefore it is necessary to develop researches to operate health-care instruments with elderly voices. In this study, a voice activity detection using a symmetric higher-order differential energy function (SHODEO) was developed and was compared with auto-correlation function(ACF) and the average magnitude difference function(AMDF). It was confirmed to have a better performance than other methods in the voice interval detection. The voice activity detection will be applied to a voice interface for the elderly to improve the accessibility of the smart devices.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.393-399
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• 2011

A defect analysis program of the composite motor case was developed to apply the ultrasonic signal processing method on basis of the ultrasonic pulse-echo method and the defects of FRP delamination and FRP/Rubber disbond in the composite motor case could be quantitatively measured. The defects detected in the composite motor case were in agreement with the results measured with the computed tomography and video microscope. This paper was described about the development process of the defect analysis program to convert the ultrasonic test data into the C-Scan image.

• Analytical Science and Technology
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• v.17 no.1
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• pp.8-15
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• 2004

The detection efficiencies of the several solid track detectors were investigated for the determination of boron content in aqueous solution by using the alpha muti-Radioisotope(RI) source. Polycarbonate (Lexan and CR-39) and cellulose nitrate (CN-85 and LR-115) were selected as materials for alpha track detection of boron. Alpha muti-RI source, uranium metal particles and boron standard solution were used for alpha emission. In this study, four solid track detectors(CN-85, LR-115, Lexan and CR-39) were characterized under various etching conditions as well as neutron irradiation conditions. As a result, the CN-85 was turned out to be best to provide good efficiency among the four detectors. The selected solid track detector was utilized for the determination of trace amount of boron in aqueous sample and its results were discussed in the text.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.323-330
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• 2009

The objective of this research was to develop a practical integrated approach using extracted features from electrical resistance measurements and coupled electromechanical models of damage, for in-situ damage detection and sensing in carbon fiber reinforced plastic(CFRP) composites. To achieve this objective, we introduced specific known damage (in terms of type, size, and location) into CFRP laminates and established quantitative relationships with the electrical resistance measurements. For processing of numerous measurement data, an autonomous data acquisition system was devised. We also established a specimen preparation procedure and a method for electrode setup. Coupon and panel CFRP laminate specimens with several known damage were tested. Coupon specimens with various sizes of artificial delaminations obtained by inserting Teflon film were manufactured and the resistance was measured. The measurement results showed that increase of delamination size led to increase of resistance implying that it is possible to sense the existence and size of delamination. A quasi-isotropic panel was manufactured and electrical resistance was measured. Then three different sizes of holes were drilled at a chosen location. The panel was prepared using the established procedures with six electrode connections on each side making a total of twenty-four electrodes. Vertical, horizontal, and diagonal pairs of electrodes were chosen and the resistance was measured. The measurement results showed the possibility of the established measurement system for an in-situ damage detection method for CFRP composite structures.