• 한국구조물진단유지관리공학회 논문집
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• 제7권1호
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• pp.267-277
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• 2003

The purpose of this study makes a retrofit and rehabilitation practice trough the analysis and the improvement for the underlying problem of current retrofit and rehabilitation methods. Therefore, the deterioration process, the damage cause, the condition classification, the fatigue mechanism and the applied quantity of strengthening methods for slab bridge decks were analysed. Artificial neural networks are efficient computing techniqures that are widely used to solve complex problems in many fields. In this study, a back-propagation neural network model for estimating a management on existing slab bridge decks from damage cause, damage type, and integrity assessment at the initial stsge is need. The training and testing of the network were based on a database of 36. Four different network models werw used to study the ability of the neural network to predict the desirable output of increasing degree of accuracy. The neural networks is trained by modifying the weights of the neurons in response to the errors between the actual output values and the target output value. Training was done iteratively until the average sum squared errors over all the training patterms were minimized. This generally occurred after about 5,000 cycles of training.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권7호
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• pp.400-405
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• 2000

In order to improve the reliability of XLPE cables, it is necessary to understand the mechanism of electrical and water tree degradation. Especially, electrical tree initiation and propagation are important in XLPE cable insulation. This paper deals with the changes of electrical properties of XLPE cable insulation with electrical tree degradation. To understand the electrical properties of XLPE insulation, specimens were prepared by 22.9kV distribution cable and made in a type of block. Ogura needles having tip radius of 10${\mu}{\textrm}{m}$ were inserted into each block pieces. AC voltages of 8kV, 10kV and 12kV at 60Hz were applied to needle. We investigated the relationship between electrical properties(PD quantity, tan$\delta$ and DC current) and the growth of electrical tree. The electrical properties of the specimens were measured from initiation of tree to breakdown and their characteristics were analyzed.

• 한국추진공학회지
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• 제11권2호
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• pp.62-70
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• 2007

지향성능은 발사차량의 정확성에 있어서 중요한 요소이다. 본 연구는 외란 가속도를 이용하여 지향구조물의 진동을 감지하는 방안과 실험 결과에 대하여 기술하였다. 주행 중 발생하는 진동 경향을 분석하기 위하여 가속도 자료를 이동평균과 힐버트 변환을 이용하여 신호 처리하였다. 다양한 외란에 대하여 가속도의 모드 계수를 얻었으며, 차량속도, 노면조건, 지향구조물의 특성을 차량 동특성의 진동을 변화시키는 요소로 간주하였다. 마지막으로 다양한 주행 조건의 진동 신호를 분류하기 위한 패턴인식에 역전파 신경망 이론을 이용하였다. 각 조건에 대하여 실험 결과를 비교 분석하였다.

• Computers and Concrete
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• 제15권2호
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• pp.305-319
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• 2015

On mesoscopic level, concrete can be treated as a three-phase composite material consisting of mortar, aggregates and interfacial transition zone (ITZ) between mortar and aggregate. A lot of research has confirmed that ITZ plays a crucial role in the mechanical fracture process of concrete. The aim of the present study is to propose a numerical method on mesoscale to analyze the failure mechanism of reinforced concrete (RC) structures under mechanical loading, and then it will help precisely predict the damage or the cracking initiation and propagation of concrete. Concrete is meshed by means of the Rigid Body Spring Model (RBSM) concept, while the reinforcing steel bars are modeled as beam-type elements. Two kinds of RC members, i.e. subjected to uniaxial tension and beams under bending, the fracture process of concrete and the distribution of cracks, as well as the load-deflection relationships are investigated and compared with the available test results. It is found that the numerical results are in good agreement with the experimental observations, indicating that the model can successfully simulate the failure process of the RC members.

• Structural Engineering and Mechanics
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• 제38권6호
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• pp.803-823
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• 2011

In this paper, the three dimensional Parallel Realistic Failure Process Analysis ($RFPA^{3D}$-Parallel) code based on micromechanical model is employed to investigate the bonding behavior in FRP sheet bonded to concrete in single shear test. In the model, the heterogeneity of brittle disordered material at a meso-scale was taken into consideration in order to realistically demonstrate the mechanical characteristics of FRP-to-concrete. Modified Mohr-coulomb strength criterion with tension cut-off, where a stressed element can damage in shear or in tension, was adopted and a stiffness degradation approach was used to simulate the initiation, propagation and growth of microcracks in the model. In addition, a Master-Slave parallel operation control technique was adopted to implement the parallel computation of a large numerical model. Parallel computational results of debonding of FRP-concrete visually reproduce the spatial and temporal debonding failure progression of microcracks in FRP sheet bonded to concrete, which agrees well with the existing testing results in laboratory. The numerical approach in this study provides a useful tool for enhancing our understanding of cracking and debonding failure process and mechanism of FRP-concrete and our ability to predict mechanical performance and reliability of these FRP sheet bonded to concrete structures.

• 한국재료학회지
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• 제28권7호
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• pp.398-404
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• 2018

Fatigue crack growth retardation of 304 L stainless steel is studied using a neutron diffraction method. Three orthogonal strain components(crack growth, crack opening, and through-thickness direction) are measured in the vicinity of the crack tip along the crack propagation direction. The residual strain profiles (1) at the mid-thickness and (2) at the 1.5 mm away from the mid-thickness of the compact tension(CT) specimen are compared. Residual lattice strains at the 1.5 mm location are slightly higher than at the mid-thickness. The CT specimen is deformed in situ under applied loads, thereby providing evolution of the internal stress fields around the crack tip. A tensile overload results in an increased magnitude of the compressive residual stress field. In the crack growth retardation, it is found that the stresses are dispersed in the crack-wake region, where the highest compressive residual stresses are measured. Our neutron diffraction mapping results reveal that the dominant mechanism is by interrupting the transfer of stress concentration at the crack tip.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.227-236
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• 2002

The purpose of this study makes a retrofit and rehabilitation practice trough the analysis and the improvement for the underlying problem of current retrofit and rehabilitation methods. Therefore, the deterioration process, the damage cause, the condition classification, the fatigue mechanism and the applied quantity of strengthening methods for RC deck slabs were analyzed. Artificial neural networks are efficient computing techniques that are widely used to solve complex problems in many fields. In this study, a back-propagation neural network model for estimating a management on existing reinforced concrete bridge decks from damage cause, damage type, and integrity assessment at the initial stage is need. The training and testing of the network were based on a database of 36. Four different network models were used to study the ability of the neural network to predict the desirable output of increasing degree of accuracy. The neural networks is trained by modifying the weights of the neurons in response to the errors between the actual output values and the target output value. Training was done iteratively until the average sum squared errors over all the training patterns were minimized. This generally occurred after about 5,000 cycles of training.

• 한국광학회지
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• 제16권6호
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• pp.481-484
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• 2005

빛의 양자역학적 성질인 얽힘(entanglement)을 이용한 양자 고스트 이미징(quantum ghost imaging)은 고전적인 동시계수 측정(classical coincidence measurement)에 의해서도 정성적으로 재현됨이 알려져 있다[1,2]. 본 실험에서는 진행방향에서 고전적인 상관관계를 가지는 빛을 이용하여 고전 동시계수 이미징(classical coincidence imaging) 실험을 수행하여 양자역학적 얽힘 상태에서 볼 수 있는 현상들을 관측하고 고스트 이미지가 나오는 원리를 분석하였다. 고전적인 상관관계를 가지는 광원은 아르곤이온 레이저에서 나오는 빛의 경로를 스피커에 부착되어 회전하는 거울에 반사시켜 진행방향에 대해 상관관계를 가지도록 만들어 사용하였다.

• Corrosion Science and Technology
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• 제10권4호
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• pp.118-124
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• 2011

Alloy 600 (Ni 75 wt%, Cr 15 wt%, Fe 10 wt%) as a heat exchanger tube of the steam generator (SG) in nuclear power plants (NPP) has been degraded by various corrosion mechanism during the long-term operation. Especially lead (Pb) is known to be one of the most deleterious species in the secondary system causing outer diameter stress corrosion cracking (ODSCC). Oxide formation and breakdown is requisite for SCC initiation and propagation. Therefore it is expected that a property change of the oxide formed on SG tubing materials by lead addition into a solution is closely related to PbSCC. In the present work, the SCC susceptibility was assessed by using a slow strain rate test (SSRT) in caustic solutions with and without lead for Alloy 600 and Alloy 690 (Ni 60 wt%, Cr 30 wt%, Fe 10 wt%) used as an alternative of Alloy 600 because of outstanding superiority to SCC. The results were discussed in view of the oxide property formed on Alloy 600 and Alloy 690. The oxides formed on Alloy 600 and Alloy 690 in aqueous solutions with and without lead were examined by using a transmission electron microscopy (TEM), equipped with an energy dispersive x-ray spectroscopy (EDXS).

• Journal of Power Electronics
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• 제16권6호
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• pp.2243-2257
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• 2016

This paper presents a two stage three-phase proton exchange membrane fuel cell (PEMFC) generation system. When the system is connected to a three-phase load, it is very sensitive to the characteristics and type of the load. Especially unbalanced three-phase loads, which result in a pulsating power that is twice the output frequency at the inverter output, and cause the dc-link to generate low frequency ripples. This penetrates to the fuel cell side through the front-end dc-dc converter, which makes the fuel cell work in an unsafe condition and degrades its lifespan. In this paper, the generation and propagation mechanism of low frequency ripple is analyzed and its impact on fuel cells is presented based on the PEMFC output characteristics model. Then a novel method to evaluate low frequency current ripple control capability is investigated. Moreover, a control scheme with bandpass filter inserted into the current feed-forward path, and ripple duty ratio compensation based on current mode control with notch filter is also proposed to achieve low frequency ripple suppression and dynamic characteristics improvement during load transients. Finally, different control methods are verified and compared by simulation and experimental results.