• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.1
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• pp.16-22
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• 1994

In contrast to the machineries using rolling element bearings, systems with journal bearings generally operate in large scale and under severe loading condition such as steam generator turbines and internal combustion engines. Failure of the bearings in these machineries can result in the system breakdown. To avoid the time consuming repair and considerable economic loss, the detection of incipient failure in journal bearings becomes very important. In this experimental approach, acoustic emission monitoring is applied to the detection of incipient failure caused by several types of abnormal operating condition most probable in the journal bearing systems. It has been known that the intervention of foreign materials, insufficient lubrication and misassembly etc. are principal factors to cause bearing failure and distress. The experiment was conducted under such designed conditions as hard particles in the lubrication layer, insufficient lubrication, and metallic contact in the simulated journal bearing system. The results showed that acoustic emission could be an effective tool to detect the incipient failure in journal bearings.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.5
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• pp.391-399
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• 2005

Laser-generated ultrasonic inspection system is a non-contact scanning inspection device with high spatial resolution and wide bandwidth. The amplitude of laser-generated ultrasound is varied according to the energy of pulse laser and the surface conditions of an object where the CW measuring laser beam is pointing. In this paper, we correct the generating errors by measuring the energy of pulse laser beam and correct the measuring errors by extracting the gain information of laser interferometer at each time. h dynamic stabilizer is developed to stably scan on the surface of an object for an laser-generated ultrasonic inspection system. The developed system generates ultrasound after adaptively finding the maximum gain time of an laser interferometer and processes the signal in real time after digitization with high speed. In this paper, we describe hardware configuration and control algorithm to build a stable laser-generated ultrasonic inspection system. Also, we confirmed through experiments that the proposed correction method for the generating errors and measuring errors is effective to improve the performance of a system.

• Proceedings of the KAIS Fall Conference
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• 2012.05a
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• pp.436-439
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• 2012

본 연구는 오존수 제조장치에 인젝터를 이용한 오존 주입방식을 도입하여 소형화, 저전력화를 실현하고자 하였다. 오존발생기, 물-오존 혼합기(인젝터), 오존용해조, 배오존 처리기로 구성된 시스템을 제작하여 인젝터 주입방식에 의한 오존수 제조장치의 오존 용해특성과 그 적용성을 검토하였다. 오존 용해 특성으로 물-공기량에 따른 인젝터 성능, 용해조에서의 오존 용해능 등을 검토하였다. 인젝터 방식은 기존의 가압용해방식에 비하여 저농도 용해능을 보였으나, 인젝터 내부의 물-오존 접촉효율이 높아 평형농도에 도달되는 시간이 단축됨을 확인하였다. 제조된 오존수의 적용 효용성은 용존오존의 잔류시간과 미생물 살균능 검사를 통하여 실시하였다. 횡형식 인젝터 시스템에 의해 용해된 용존오존의 잔류시간이 기존의 가압용해방식에 비하여 다소 짧았으나 미생물의 살균능에는 크게 차이가 나지 않았다.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.177-184
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• 2012

An optical defect detection method using ESPI(electronic speckle pattern interferometry) is proposed. ESPI is widely used as a non-contact measurement system which show deformation and phase map in real time. ESPI can be divided as the in-plane, out-of-plane and shearography by operation principle and target object and also divided with bulk type and optic fiber type by the optic configurations. This paper is focused on optic fiber type out-of-plane ESPI, which has the following advantages: (1) low cost; (2) reduction of the unreliable factors generated by separated optic components; (3) simplification of the optic configuration; (4) great reduction of volume; (5) flexibility, to be easily designed into different structures to adapt to inaccessible environments such as pipeline cavity and so on.

• Journal of the Korean Magnetics Society
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• v.20 no.2
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• pp.45-51
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• 2010

We suggest the algorithm that it detects volume and shape according with a variation of magnetic field in non-contact electromagnetic measurement system. It is possible to assess an object shape through a variation of magnetic field. The basic idea is compared a length difference with a variation of magnetic field in a detected object and a circle which modeled equivalent area. And the shape is detected to many calibration process that it is similar to signal pattern between a length difference and a variation of magnetic field in object and equivalent circle. This is the shape detection algorithm that use only the variation of magnetic field. In this paper, it has application to the shape detection algorithm about the object as hexagon, pentagon, rectangle, trigon. we can detect the object shape easily because the shape detection algorithm is only used to the variation of magnetic field.

• 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 for Nondestructive Testing
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• v.14 no.2
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• pp.101-111
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• 1994

Electronic speckle pattern interferometry(ESPI) using a CW laser, a video system and an image processor were applied to the in-plane displacement measurements. Unlike traditional strain gauges or Moire method, ESPI method requires no special surface preparation or attachments and it can be measured in-plane displacement without any contact and real time. In this experiment, specimen was loaded in paralled with a loa cell. The specimen was plance to which strain gauges was attached. The study provides an example of how ESPI have been used to measure displacement and strain distribution in this specimen. The results measured by ESPI were compared with the data which were measured by strain gauge method in tensile testing.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.5
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• pp.349-355
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• 2014

Wall thinning defects can occur in the pressure vessels used in a variety of industries. Such defects are related to the flow velocity. Considering the fact that such vessels constitute up to 70 or 80% of the plant structures in a power plant, it is important to measure internal defects as part of a safety evaluation. In this study, optical measurement were applied in a non-destructive evaluation using shearography to ensure the safety and improve the reliability of a power plant through the non-contact, non-destructive evaluation of pressure vessels. In order to verify whether the pressure vessels contained faults, experimental and analytical investigation were conducted to measure any internal defects and out-of-plane deformation from inner temperature changes and pressure changes in the piping of the circulation system. The most important factors in this research were the thickness, width, and length of a defect. An increase in these could confirm an increase in the deformation. Thus, internal defects in a pressure vessel were measured using shearography, which made it possible to ensure the reliability and integrity of the pipe.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.15-21
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• 2004

It is possible to detect flaws in pipelines without interruption using all EMAT transducer because it is a non-contact transducer which can transmit ultrasonic waves into specimens without couplant. And it ran easily generate guided waves desired in each specific problem by altering the design of coil and magnet. In the present work, EMAT systems have been fabricated to generate surface waves, and selectively the plate wave of $A_1\;or\;S_1$ mode. The surface wave of 1.5MHz showed a good signal-to-noise ratio without distortion in its propagation along a pipeline, while the $S_1$ mode of 800kHz and the $A_1$ mode of 940kHz were distorted according to their dispersive properties. The wider the excitation pulse becomes, the better the mode selectivity of the plate waves becomes. A pipe of 256mm inner diameter and 5.5m thickness with 5 flaws was used for comparing the flaw detectability among the modes under consideration.

• 한국정보통신설비학회:학술대회논문집
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• 2004.08a
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• pp.6-10
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• 2004

회전기기의 운전 상태에서 on-line 부분 방전시험은 고정자 권선의 절연상태를 검사, 평가 할 수 있는 중요한 수단으로서 이러한 부분방전시험을 통하여 회전기기 시스템의 사고예방을 위한 진단을 할 수 있다. 기존의 비접촉식 센서인 SSC는 부분방전 측정을 위하여 권선의 웨지 아래에 설치하는 방식으로 개발되어 [1], 설치가 불편하고 Global VPI 방식으로 제작된 소형 회전기에는 설치할 수 없는 단점이 있다. 본 논문에서는 소형 회전기에 사용가능한 저, 고주파용 부분방전 센서를 제안하였다. 웨지 위에 설치 가능한 SSC 형태의 마이크로스트립 센서 및 전송선로 이론을 이용한 2선 평행 전송선로 센서는 값이 싸고 소형 회전기에 설치할 수 있을 정도의 크기를 지니며, 기본적으로 센서의 구조가 고주파 웨이브가이드로서 고주파용 센서로 적합하다. 또한 저주파 신호를 검출하기 위한 센서로 로고우스키 코일 형태의 U 타입 센서는 와전류를 검출하는 센서로서 슬롯 외부에 설치 되어야 한다. 이러한 U 타입 센서와 마이크로스트립 센서 또는 2선 평행 전송선로를 동시에 설치할 경우 저, 고주파를 효과적으로 검출할 수 있다.