• Smart Structures and Systems
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• v.1 no.2
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• pp.185-215
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• 2005

Advanced signal processing techniques have been long introduced and widely used in structural health monitoring (SHM) and nondestructive evaluation (NDE). In our research, we applied several signal processing approaches for our embedded ultrasonic structural radar (EUSR) system to obtain improved damage detection results. The EUSR algorithm was developed to detect defects within a large area of a thin-plate specimen using a piezoelectric wafer active sensor (PWAS) array. In the EUSR, the discrete wavelet transform (DWT) was first applied for signal de-noising. Secondly, after constructing the EUSR data, the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) were used for the time-frequency analysis. Then the results were compared thereafter. We eventually chose continuous wavelet transform to filter out from the original signal the component with the excitation signal's frequency. Third, cross correlation method and Hilbert transform were applied to A-scan signals to extract the time of flight (TOF) of the wave packets from the crack. Finally, the Hilbert transform was again applied to the EUSR data to extract the envelopes for final inspection result visualization. The EUSR system was implemented in LabVIEW. Several laboratory experiments have been conducted and have verified that, with the advanced signal processing approaches, the EUSR has enhanced damage detection ability.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.357-360
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• 2002

혈관에 흐르는 혈류 속도의 측정은 혈압 및 심박수와 관련된 혈류의 역학적 변화를 관찰하는 데 있어서 주로 사용되는 방법 중의 하나이다. 이 혈류 속도는 일반적으로 도플러 효과에 의하여 주파수가 변화하는 현상을 이용하여 추정하게 된다. 그런데 기존의 주파수 추정 방법들은 시불변 시스템을 가정하고 있지만 실제 혈관 속은 혈구가 일정하지 않은 속도를 갖는 시변 시스템이라 할 수 있기 때문에 이러한 시변 특성이 강한 경우 기존의 방법을 이용하게 되면 그 성능이 저하되는 경향을 보인다. 또 피시험자의 몸 상태에 따라서 서로 다른 주파수 변화 추이를 보이므로 하나의 고정 변수로써 최적화된 성능을 기대하기도 어렵다. 그러므로 본 논문에서는 시변 시스템에서 좋은 성능을 갖는 가변 망각 인자(variable forgetting factor, VFF)를 사용한 순환적인 완전 최소 자승법(recursive total least squares, RTLS) 기법을 이용한 주파수 추정 방법을 제안한다. RTLS란 TLS 기법을 순차적으로 계산하는 방법으로 시변 적응력을 향상시키는 방법이다. 또한 이 기법에 가변 망각 인자(VFF)를 적용시키는 것은 시변 시스템에서 외부적인 변화에 대하여 좀더 효율적으로 대응할 수 있기 위함이다. 기존의 방법과 성능 비교를 위하여 컴퓨터 시뮬레이션을 하였으며 그 결과 시변 시스템에서 본 논문에서 제안한 VFF를 이 용한 RTLS 기법이 보다 향상된 성능을 가지고 있음을 확인 할 수 있었다.

• Computers and Concrete
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• v.15 no.4
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• pp.503-514
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• 2015

Fibre-added concretes are frequently used in large site applications such as slab and airports as well as in bearing system elements or prefabricated elements. It is very difficult to determine the mechanical properties of the fibre-added concretes by experimental methods in situ. The purpose of this study is to develop an artificial neural network (ANN) model in order to predict the compressive and bending strengths of hybrid fibre-added and non-added concretes. The strengths have been predicted by means of the data that has been obtained from destructive (DT) and non-destructive tests (NDT) on the samples. NDTs are ultrasonic pulse velocity (UPV) and Rebound Hammer Tests (RH). 105 pieces of cylinder samples with a dimension of $150{\times}300mm$, 105 pieces of bending samples with a dimension of $100{\times}100{\times}400mm$ have been manufactured. The first set has been manufactured without fibre addition, the second set with the addition of %0.5 polypropylene and %0.5 steel fibre in terms of volume, and the third set with the addition of %0.5 polypropylene, %1 steel fibre. The water/cement (w/c) ratio of samples parametrically varies between 0.3-0.9. The experimentally measured compressive and bending strengths have been compared with predicted results by use of ANN method.

• Nuclear Engineering and Technology
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• v.36 no.6
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• pp.540-548
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• 2004

Check valve failure is one of the worst problems in nuclear power plants. Recently, many researches have been based on new technology using accelerometers and ultrasonic and magnetic flux detection have been carried out. Here, we have suggested a method that uses acoustic emission sensors for detecting the failures of check valves through measuring and analyzing backward leakage flow, a system that works without disassembling the check valve. For validating the suggested acoustic emission sensor methodology, we designed a hydraulic test loop with a check valve. We have assumed in this study that check valve failure is caused by disk wear or by the insertion of a foreign object. In addition, we have developed diagnostic algorithms by using a neural network model to identify the type and size of the failure in the check valve. Our results show that the proposed diagnostic algorithm with acoustic emission sensors is a good solution for identifying check valve failure without necessitating any disassembly work.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1921-1925
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• 2010

개수로의 흐름을 측정하는 유속계는 유체역학 및 수리학적 연구와 유량 측정 등의 업무에 필수적인 장비이다. 그동안 국내에서는 일부 전자파표면유속계(이상호 등, 1997)와 영상처리 기반의 LSPIV(김영근 등, 2004)와 같은 비접촉식 유속측정 장치가 개발되어 활용되고 있지만, 유속 및 유량 측정에 보다 널리 사용되고 있는 수중 투입식 유속계의 경우 거의 개발되지 않았다. 특히 유속 분포를 측정하는데 활용될 수 있는 초음파 방식 유속 프로파일러는 거의 전적으로 외국제품에 의존하고 있다. 일반 유속계가 점유속을 측정하는데 비해 유속 프로파일러는 센서가 지향하는 방향선을 따라 공간적인 유속분포를 동시에 획득할 수 있으므로 측정 효율성이 높다는 장점을 지닌다. 본 연구에서는 국내 기술로 개수로 흐름 측정에 활용할 수 있는 초음파 유속 프로파일러를 개발하였다. 이 유속 프로파일러는 초음파 펄스를 반복적으로 송수신하는 PRF 기법을 이용하여 개발하였다. 개발된 유속 프로파일러는 직사각형 수로에서 유속 분포를 측정하기 위해 적용하였으며, 기존의 2차원 유속계와 그 결과를 비교하였다. 본 연구에서 개발한 유속 프로파일러는 실제 하천에 활용하기에는 측정 가능한 유속 및 수심 범위의 한계가 있으나 PRF 기법의 한계 범위에서는 실측 유속분포를 비교적 잘 재현하는 것으로 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1405-1409
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• 2010

최근 우리나라는 물 부족 국가로서 물의 효율적 관리 필요성 증대, 기후변화에 따른 가뭄 홍수 피해 증가 등으로 신뢰성 있는 수문자료구축이 필요성이 요구되고 있다. 그 중 유량측정 분야는 모든 수자원 계획과 관리의 근간이 되는 분야로 그 중요성 또한 간과 할 수 없는 부분이다. 현재 우리나라에서는 한국건설기술연구원 산하 유량조사사업단에 의해 유량측정 주요지점에 자동유량측정 시설을 설치하고 이를 운영함으로써 각 지점의 특성에 따라 적절한 방식을 채택하여 이동시간차방식 초음파 유속계(UVM, Ultrasonic Velocity Meter)와 도플러방식 초음파유속계(ADVM, Acoustic Doppler Velocity Meter)를 설치하면서 향후 수문계측 분야 선진화를 위한 기초자료를 제공하고 있다. 하지만 실시간 무인화 계측시스템에 의해 제공되는 자료가 양질의 자료임을 보장할 수 없는 현실이기 때문에 측정된 기초자료의 필터링을 통한 자료의 질적 개선이 필요하다. 따라서 본 연구에서는 기존에 전산분야의 필터링 방법으로 널리 알려져 있는 LPF(Lowpass Filter)와 KF(Kalman Filter)를 이용하여 자동유량측정 자료의 필터링 방법으로 활용하고, 그 적용성을 검토하였다. 본 연구를 통해 기존 유량자료의 문제점을 개선하고 효율적인 유량조사를 위한 기초자료 확보 방법으로 활용될 수 있을 것으로 기대된다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.1
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• pp.21-30
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• 1999

The research for retecting of insulating deterioration in transforrrer has been studied from long ago and the analysis rrethod of combustible gas which is included in insulating oil has been used Recently the spreading effect of the accident is larger than before because of high voltage and large capacity, so on-line detecting system is needed and the study for the estimation of partial discharge signals location has begun. This thesis is the study for the sermating noise signal that is the greatest problem in ultrasonic signal measurement which is one of the method of estimation of partial discharge signals location. Because we can measure the number and location of signal, it is rossible to distinguish between the signal of partial discharge and the external noise. Therefore, we can devolop the credibility of detecting of insulating deterioration in transformer.former.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1183-1188
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• 2011

The novel metal position detection method is proposed where conventional techniques, in high temperature, moisture and particle environment, are not able to be applied. It is known that electronic devices, utilizing microwave, ultrasonic or optical technique, are hard to apply for sensing application where temperature is exceeding above 300 degree centigrade. Metal position detection technique, which was consisted with passive elements facing hot sensing surface, utilizing electromagnetic wave was investigated, and the metal detection sensitivity was measured by varying sensor frequency and sensing distance. Measurement result in laboratory test set-up showed position measurement resolution up to 1mm, when distance between two sensing elements were 500mm, and possibility to measure position of hot metal sheet having very high surface temperature.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.4
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• pp.215-225
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• 2001

Stress waves monitored on the surface of structures under various loading conditions can provide useful information on the structural health status. In this paper, stress waves are measured by several sensors when a steel beam is impacted by a ball drop. The sensors used include the piezo-electric film Sensor, the electrical strain gage, and the ultrasonic transducer, and special attention is given to the pieza film sensor. The wavelet transform is used for the time-frequency analysis of dispersive waves propagating in the beam. The velocities of the wave produced in the team due to the lateral impact is found to be frequency-dependent and identified as the flexural wave velocity based on the comparisons with the Timoshenko beam theory. A linear impact site identification method is developed using the flexural wave, and the impact sites of the beam can be accurately estimated by the piezo film sensors. It is found that the piezo film sensor is appropriate for sensing stress waves due to impact and for locating impact sites in the beam.

• Journal of the Korean Society of Safety
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• v.26 no.5
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• pp.17-22
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• 2011

This study proposes feature extraction method of pattern recognition by evaluation of weld defects in weld zone of titanium. For this purpose, analysis objectives in this study are features of attractor quadrant and fractal dimension. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics resulting from distance shifts such as porosity of weld zone. These differences in characteristics of weld defects enables the evaluation of unique characteristics of defects in the weld zone. In quantitative fractal feature extraction, feature values of 0.87 and 1.00 in the case of part of 0.5 skip distance and 0.72 and 0.93 in the case of part of 1.0 skip distance were proposed on the basis of fractal dimensions. Attractor quadrant point, feature values of 1.322 and 1.172 in the case of ${\phi}1{\times}3mm$ porosity and 2.264 and 307 in the case of ${\phi}3{\times}3mm$ porosity were proposed on the basis of distribution value. The Proposed feature extraction of pattern recognition in this study can be used for safety evaluation of weld zone in titanium.