• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.465-470
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• 1996

본 연구는 원자로 RPV(Reactor Pressure Vessel)를 두 개의 이상적인 입체 구조물 즉, 원통면과 반구로 나누어, 원통면에서의 충격위치를 검출할 수 있는 알고리즘을 제안하고 그 효용성을 고찰하는데 있다. 현재 사용중인 원전내네 금속파편 감시계통(LPMS : Loose Parts Monitoring System)의 경우 충격신호를 레코더에 저장하고 전문가를 통해 데이터베이스화된 기준신호와 비교 분석하는 Off-line분석방법을 사용해 왔다. 그리나 이러한 방법은 많은 소요시간을 가지므로 손상잠재성이 큰 경우 즉각적인 대처를 할 수가 없다는 단점을 가진다. 따라서 본 논문에서는 이러한 방법을 지양하고 센서로부터 얻은 충격신호를 분석컴퓨터에 입력하여 즉각적으로 충격위치를 찾을 수 있는 On-line분석방법을 제안함에 있어, 기초적 연구로서 원통면에서의 충격위치 검출방법을 제시하였다.

• Journal of Aerospace System Engineering
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• v.13 no.2
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• pp.19-25
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• 2019

To detect the impact location of a structure, the authors' group conducted a study on piezoelectric paint sensor. The piezoelectric paint sensors are used for impact detection due to their inherent characteristics: sensitivity to high-frequency signal and impact. Additionally, the paint sensor can be applied on curved and complex structures where ceramic sensor would not be applicable. Moreover it is a self-powered sensor therefore no need for an external power source. For impact localization, mosaic pattern electrodes were coated on the specimen and the impact signal obtained from any part of the electrode where the impact occurred. If we more precise impact localization is required, the electrodes should be divided into more parts and impact data acquisition conducted in all the points of the electrode. In this paper, we developed a light, cheap and simple multi-channel data acquisition system to aid in data gathering. In total four channels data acquisition have been tested using the ARM Cortex-M3.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.37-42
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• 2004

In order to monitor the impact locations in smart structures, multipoint ultrasonic sensors are to be employed. In this study, a multiplexing demodulator with wide dynamic range was proposed to detect the impact locations using FBG sensors, and a stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. Two FBG sensors were attached on the bottom side of the aluminum beam specimen and low velocity impact tests were performed to detect the one-dimensional impact locations. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely, and found the impact locations with the average location error below 0.58mm.

• Composites Research
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• v.13 no.1
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• pp.40-49
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• 2000

The objective of this research is to develop the impact monitoring techniques providing impact identification and damage diagnostics of smart composite laminates susceptible to impacts. This can be implemented simultaneously by using the acoustic waves by the impact loads and the acoustic emission waves from damage. In the previous research, we have discussed the impact location detection process in which impact generated acoustic waves are detected by PZT using the improved neural network paradigm. This paper describes the implementation of time-frequency analysis such as the Short-Time Fourier Transform (STFT) and the Wavelet Transform (WT) on the determination of the occurrence and the estimation of damage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1335-1343
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• 2014

Piezoelectric paint can be used to monitor vibrations or impacts occurring in large engineering structures such as ships and airplanes. This study investigated the impact detection characteristics of a piezoelectric paint sensor and possible errors in detecting impacts according to boundary conditions. The piezoelectric paint sensor used in this study was coated on an aluminum plate with four different electrode areas. After the occurrence of the poling process, the output voltages from the paint sensors were obtained when impact occurred in a certain sensor region. The experimental results revealed a large difference in magnitudes between the sensor signal in the impact region and those in the other regions, and this relation was maintained regardless of the changes in the boundary conditions.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.166-171
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• 1997

LPMS(Loose Part Monitoring System)는 원자로 및 냉각재계통내에서 발생하는 금속파편의 검출 및 분석을 위하여 사용되는 진단 장비이다. 본 논문에서는 RPV(Reactor Pressure Vessel)의 상부헤드(closure head)와 하부헤드(lower head)에서의 금속파편의 충격위치를 평가하는 LPMS를 위한 새로운 기법을 제안하고, Mock-up에서의 실험을 통하여 그 효용성을 검증하였다. 즉, 수정된 원교차법을 제안하고, 이를 반구로 모델링된 RPV의 상ㆍ하부헤드에 존재하는 금속파편의 위치평가에 적용하므로써 정확한 충격위치를 찾을 수 있음을 보였다. 이들 결과는 충격물질의 질량이나 에너지를 계산하는데 정확한 정보를 제공해 줄 수가 있다.

• The Journal of the Acoustical Society of Korea
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• v.30 no.2
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• pp.73-79
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• 2011

This paper presents a new impulsive noise detection algorithm in speech signal. The proposed method employs the frequency domain characteristic of the impulsive noise to improve the detection accuracy while avoiding the false-alarm problem by the pitch of the speech signal. Furthermore, we proposed time-frequency domain impulsive noise detector that utilizes both the time and frequency domain parameters which minimizes the false-alarm problem by mutually complementing each other. As the result, the proposed time-frequency domain detector shows the best performance with 99.33 % of detection accuracy and 1.49 % of false-alarm rate.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.221-230
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• 2000

The usefulness and limitations of the impact-resonance method, which is a nondestructive evaluation (NDE) method for concrete, are studied by both experimental and theoretical methods. For the experimental study, several concrete slab specimens with various inclusions embedded were fabricated, and tested by the impact-resonance method. Some of the inclusions have been detected and accurately located, but some have not. The reasons for the failure in the latter cases have been investigated theoretically by using finite element analyses, from which the primary factors determining the success of the method have also been identified. This study will serve to enhance the understanding of the underlying physics and to improve the usefulness of the impact-resonance method as applied to concrete NDE.

• Composites Research
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• v.13 no.1
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• pp.89-97
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• 2000

Fatigue damage detection and vibration sensing for a laminated composites and impact location detection for a steel beam have been carried out using optical fiber sensor. Intensity based optical fiber sensor is constructed by placing two cleaved fiber end in a hollow glass tube, and multiple reflection within the cavity is considered. Fatigue signals are measured by embedded optical fiber, surface mounted optical fiber sensor and strain gage simultaneously. For vibration sensing, optical fiber sensor is mounted on the carbon fiber composite beam and its response to free vibration and forced vibration is investigated. In impact location detection, two optical fiber sensors are used and the information obtained from two sensors is arrival time delay of vibration caused by impact. Impact location can be calculated from this time delay. The obtained results show that the intensity based optical fiber sensor provide reliable data during long-term fatigue loading, unlike strain gage which deteriorate during the early part of the fatigue test. Optical fiber sensor signals coincide with gap sensor in vibration sensing. The precise locations of impact can be detected within 4.1% error limit.

• Composites Research
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• v.13 no.5
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• pp.1-9
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• 2000

An intensity-based optical fiber vibration sensor is applied to monitor the structural vibration and detect impact locations on a plate. Optical fiber vibration sensor is constructed by placing two cleaved fiber end, one of which is cantilevered in a hollow glass tube. The movement of the cantilevered section lags behind the rest of the sensor in response to an applied vibration and the amount of light coupled between the two fibers is thereby modulated. For vibration sensing, optical fiber vibration sensor is mounted on the carbon fiber composite beam and its response is investigated to free and forced vibration. In impact location detection, four optical fiber vibration sensors whose location is predetermined are placed at chosen positions and the different arrival times of impact-generated vibration signal are recorded by an FFT analyzer. Impact location can be calculated from these time delays. Experimental results show that optical fiber vibration sensor signals coincide with gap sensor in vibration sensing. The precise location of impact can be detected on an acrylate plate.