• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.165-174
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• 2011

This research aims at the optimal constitution of sensors required to identify the structural shortcoming of roller-coaster. In this research we analyzed the dynamic characteristics of roller-coaster by three dimensional FE modelling, decided on the appropriate location and number of sensors through optimal transducer theory, abstracted the mathematical value of modal features before and after damage on the basis of optimally placed and numbered sensors. and then presented it as a primary information about the basic structure which would be applied to damage estimation. As a target structure, the roller-coater at Seoul Children's Grand Park was chosen and built as a model reduced by one twentieth in size. In order to consider the Kinetics features particular to the roller-coaster structure, we made an exact three-dimensional FE modelling for the model structure by means of Spline function. As for the proper location and number of sensors, it was done by applying EIM and EOT. We also estimated the damage from the combination of strength, flexibility, and model corelation after abstracting the value of modal features. Finally the optimal transducer theory presented here in this research was proved to be valid, and the structural damage was well identified through changes in strength and flexibility. As a result, we were able to present the optimal constitution of sensors needed for the analysis of dynamic characteristics and the development of techniques in dynamic characteristics, which would ultimately contribute to the development of health monitoring for roller-coaster.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.485-492
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• 2009

The thermal fatigue crack(TFC) is one of the life-limiting mechanisms at the nuclear power plant operating conditions. In order to evaluate the structural integrity, various non-destructive test methods such as radiographic test, ultrasonic test and eddy current are used in the industrial field. However, these methods have restrictions that defect detection is possible after the crack growth. For this reason, acoustic emission testing(AET) is becoming one of powerful inspection methods, because AET has an advantage that possible to monitor the structure continuously. Generally, every mechanism that affects the integrity of the structure or equipment is a source of acoustic emission signal. Therefore the noise filtering is one of the major works to the almost AET researchers. In this study, acoustic emission signal was collected from the pipes which were in the successive thermal fatigue cycles. The data were filtered based on the results from previous experiments. Through the data analysis, the signal characteristics to distinguish the effective signal from the noises for the TFC were proven as the waveform difference. The experiment results provide preliminary information for the acoustic emission technique to the continuous monitoring of the structure failure detection.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.23-32
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• 2020

The compression sensing technology, CAFB, was developed to obtain the raw signal of the target structure by compressing it into a signal of the intended frequency range. At this point, for compression sensing, the CAFB can be optimized for various reference signals depending on the desired frequency range of the target structure. In addition, optimized CAFB should be able to efficiently compress the effective structural answers of the target structure even in sudden/dangerous conditions such as earthquakes. In this paper, the targeted frequency range for efficient structural integrity monitoring of relatively flexible structures was set below 10Hz, and the optimization method of CAFB for this purpose and the seismic response performance of CAFB in seismic conditions were evaluated experimentally. To this end, in this paper, CAFB was first optimized using Kobe seismic waveform, and embedded it in its own wireless IDAQ system. In addition, seismic response tests were conducted on two span bridges using Kobe seismic waveform. Finally, using an IDAQ system with built-in CAFB, the seismic response of the two-span bridge was wirelessly obtained, and the compression signal obtained was cross-referenced with the raw signal. From the results of the experiment, the compression signal showed excellent response performance and data compression effects in relation to the raw signal, and CAFB was able to effectively compress and sensitize the effective structural response of the structure even in seismic situations. Finally, in this paper, the optimization method of CAFB was presented to suit the intended frequency range (less than 10Hz), and CAFB proved to be an economical and efficient data compression sensing technology for instrumentation-monitoring of seismic conditions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.635-650
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• 2017

Acoustic emission (AE) sensors have broadly used to monitor the damage of underground structures and tunnels. The reliability of measured signal is determined by the coupling condition of the AE sensors which are embedded in the target underground structure. To secure the reliability of health monitoring results, it is important to understand the characteristics of the coupling materials. In this study, laboratory tests were performed using portland cement, micro cement, and gypsum as coupling materials in order to verify the bleeding characteristics. The effective parameters for bleeding were determined to be water-cement ratio, material type, curing time, and injected volume of coupling materials. As a results of the experimental study, the bleeding rate increases with an increase in a water-cement ratio and an injected volume; for portland cement, water-cement ratio and injected volume effects are larger than the micro cement. However, curing time is not much effective for occurrence of the bleeding phenomenon. It is anticipated that this study may be useful for the selection of suitable coupling materials for installation of acoustic emission sensors.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.8
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• pp.887-895
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• 2012

Lamb waves have received a great attention in the structural health monitoring (SHM) societies because they can propagate over relatively large distances in wave guides such as thin plates and shells. The time-of-flights of Lamb waves can be used to detect damages in a wave guide. However, due to the inherent dispersive and multi-mode characteristics of Lamb waves, one must decompose the Lamb wave modes into the symmetric and anti-symmetric modes for SHM applications. Thus, this paper proposes a decomposition method for the two-mode Lamb waves based on two rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of fundamental symmetric and anti-symmetric modes is constant, while the mode amplitude ratio rule means that the magnitude of the fundamental symmetric modes of all measured response signals should be always larger than those of the anti-symmetric mode once the input signal is applied so that the magnitude of fundamental symmetric mode of excited Lamb-wave is larger than that of anti-symmetric mode, and vice versa. The proposed method is verified through the experiments ducted for an aluminum plate specimen.

• Composites Research
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• v.31 no.4
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• pp.145-150
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• 2018

Various structural health monitoring (SHM) systems have been suggested for aerospace industry in order to increase its life-cycle and economic efficiency. In the case of aircraft structure madden with metal, a major concern was hot spots, such as notches, bolts holes, and where corrosion or stress concentration occurs due to moisture or salinity. However, with the increasing use of composites in the aerospace industry, further advanced SHM systems have been being required to be applied to composite structures, which have much complex damage mechanism. In this paper, a method of acoustic emission localization for composite structures using Q-switched laser and multiple Amplifier-integrated PZTs have been proposed. The presented technique aims at localization of the AE with an error in distance of less than 10 mm. Acoustic emission simulation and the localization attempt were conducted in the composite structure to validate the suggested method. Localization results, which are coordinates of detected regions, grid plots and color intensity map have been presented together to show reliability of the method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.267-273
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• 2002

이 논문은 계측신호 분석에 의한 교량구조물의 건전성 모니터링에 관한 것으로, 2 단계 인공신경망을 사용한 구조물의 손상발견 기법에 대하여 제안하고 있다. 첫 번째 단계의 인공신경망은 구조물로부터 측정된 가속도 신호를 입력으로 사용하여 각각의 가속도계로부터 측정된 신호의 변형정도를 나타내는 신호변형지수를 출력하도록 설계되었다. 손상의 발생 여부를 나타내는 첫 번째 단계 인공신경망의 출력값은 다시 두 번째 단계 인공신경망의 입력으로 사용되어 손상의 위치와 정도를 파악하는데 쓰여진다. 모형교량을 사용한 실험으로부터 얻어진 가속도신호를 사용하여 제안된 방법의 타당성을 확인하였으며, 항후 실 교량에 대한 실험을 통하여 현장 적용의 가능성을 확인할 계획이다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.44-47
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• 2011

본 논문에서는 상사진동에서의 응답을 통해 구성된 모드유연도 행렬에 의해 추정되는 변위/변형을 이용해 전당빌딩의 손상을 정량적으로 평가하는 방법을 제시하였다. 제안된 방법은 전단빌딩의 손살발생 후의 층간변위와 손상발생 전 후의 층간변위 차이인 Damage-induced inter-story deflection(DI-ID)의 관계를 이용해 손상을 정량적으로 평가하는 방법이다. 구조물이 양전단력만을 발생시킴으로써 층간변위를 분명히 파악할 수 있도록 하는 양전단력 탐색하중(Positive Shear Inspection Load)을 통해 DI-ID를 산정한다. 제안된 방법의 검증을 위해 5층의 전단빌딩 축소모형을 대상구조물로 선정했으며, 단일손상과 다중손상의 모사를 위해 1층과 3층의 휨강성을 각각 10% 씩 저감시켰다. Static test와 modal test를 통해 각각의 결과를 비교하는 방법으로 제안된 방법의 성능검증을 수행했으며, 축소모형실험 결과, 두 실험간 평균오차 1% 이내로 정확도를 검증했다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.195-195
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• 2021

최근 기후변화, 과도한 지하수 이용 등으로 유역 환경이 변화하고 있으며, 이에 따른 부작용으로 하천의 건천화, 지표유출량 증가, 증발산량 감소 등 물순환 구조가 왜곡되고 있다. 물순환 과정은 지역적 조건에 따라 다르게 나타나며, 모의 요소와 해석 기법도 다르다. 따라서 지속가능하고 건전화된 물순환을 위해 해당 유역의 물순환계를 정확히 파악하고 고려하여 객관적으로 정량화할 수 있어야 한다. 현재 우리나라 농업유역은 논, 용·배수로, 농업용 저수지가 존재하며, 종합적인 농촌용수 물순환 해석을 위해 농촌용수 요소별 해석 기술 및 모듈 개발, 모델링 기법 등을 이용하여 농촌수자원의 체계적·과학적 해석 및 관리 시스템 개발이 이루어져야 한다. 본 연구에서는 강원도 원주시에 위치한 흥업저수지를 대상으로 농촌용수의 물순환 과정을 정립하였으며, 저수지 시점부·말단부, 농업용 저수지, 저수지 유역으로 구분하여 물순환 분석을 수행하였다. 물순환 모의 요소로 저수지 수위, 유역 유출량, 수로부 공급량 및 배수량, 회귀수량 등으로 선정하였으며, 수로 네트워크 기반의 SWMM (Storm Water Management Model) 모형을 이용하여 종합적인 농촌용수 물순환 해석을 수행하였다. 또한, 물순환 해석 기법의 적용성 검증을 위해 모의 요소별 모니터링을 수행하였으며, SWMM 모형과 모니터링을 비교하여 적용성을 평가하였다. 본 연구 결과를 통해 농촌지역 특성 및 기후변화를 고려한 농촌수자원의 안정적인 공급과 국가 청정 수자원 확보를 위한 통합 물관리 정책을 실현하는데 기초 자료로써 활용 가능할 것이라 사료된다.

• Journal of the Korean Geophysical Society
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• v.7 no.4
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• pp.269-276
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• 2004

Optical fiber sensors have shown a potential to serve real time health monitoring of the structures. They can be easily embedded or attached to the structures and are not affected by the electro-magnetic field. Furthermore, they have the flexibility of the sensor size and very highly sensitive. In this study, we conducted several laboratory and field tests using a novel optical sensor based on Brillouin scattering. One of the advantages of this technique is that the bare fiber itself acts as sensing element without any special fiber processing or preparation. Test results have shown that BOTDR can be a great solution for sensor systems of Civil Engineering Smart Structures.