• 한국철도학회논문집
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• 제13권6호
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• pp.608-616
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• 2010

서울지하철 5,6,7,8호선을 운영하는 서울도시철도공사는 연장 152km, 148개 역사에 분산되어 있는 시설물에 대하여 점검과 유지보수를 하고 있다. 장애예방을 위한 철저한 점검에도 불구하고 지하역사의 환경적인 요인, 빈번한 사용으로 인한 기계적인 마모, 시설물 노후화, 시스템 에러, 이용 상의 부주의 등으로 장애가 지속적으로 발생하고 있다. 서울도시철도공사에서는 지금까지 관행적으로 수행해 오던 시설물 점검방법과 유지보수의 틀을 깨고 정량적인 목표관리와 일하는 방식 변화 등을 통해 2010년 6월말까지 장애를 연간 53.4% 감소시켰다. 본 논문에서는 기존 도시철도 시설물 점검 및 유지보수의 문제점을 분석하고, 이를 개선하기 위해 추진했던 장애감소 전략과 각각의 추진성과를 분석한다.

• Journal of Information Technology Applications and Management
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• 제13권2호
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• pp.17-28
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• 2006

The SRGM has been studied under the assumption that S/W reliability can grow as the fault causing failure is removed even during operational phase because the debugging is available. On the other hand, some papers insist on the uniform failure rate during operational phase because the debugging may not be available in case of universal software. The phenomenon, however, has been observed informally many times that the products S/W reliability grows as the time goes by even without any debugging in point of customer view. I propose the simple approaching method to model the S/W reliability phenomenon that the failure rate reduces as time goes on without modifying the existing reliability model in this paper.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.427-436
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• 2017

Concrete technologists have used ultrasonic pulse velocity test for decades to evaluate the properties of concrete. However, the presented research work focuses on the use of ultrasonic pulse velocity test to study the degradation in steel-concrete bond subjected to increasing loading. A detailed experimental investigation was conducted by testing five identical beam specimens under increasing loading. The loading was increased from zero till failure in equal increments. From the experimentation, it was found that as the reinforced concrete beams were stressed from control unloaded condition till complete failure, the propagating ultrasonic wave velocity reduced. This reduction in wave velocity is attributed to the initiation, development, and propagation of internal cracking in the concrete surrounding the steel reinforcement. Using both direct and semidirect methods of testing, results of reduction in wave velocity with evidence of internal cracking at steel-concrete interface are presented. From the presented results and discussion, it can be concluded that the UPV test method can be successfully employed to identify zones of poor bonding along the length of reinforced concrete beam. The information gathered by such testing can be used by engineers for localizing repairs thereby leading to saving of time, labor and cost of repairs. Furthermore, the implementation strategy along with real-world challenges associated with the application of the proposed technique and area of future development have also been presented.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2008년도 춘계학술대회 논문집
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• pp.285-288
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• 2008

Even though many modular converters have several internal protection circuit blocks for various abnormal operation conditions, there are many failure cases on modular converters at real applications. In this paper, the control strategy for failure protection of converters with internal 'In-Hibit' function is investigated. As an example, for the MDl modular converters the in-hibit function application is realized and the test results shows that adopting in-hibit function while converter switching reduces the voltage and current stress. And the reduction of switching stress on converter will decrease failure rate on converters.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.271-282
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• 2022

The active learning surrogate model based on adaptive sampling strategy is increasingly popular in reliability analysis. However, most of the existing sampling strategies adopt the trial and error method to determine the size of the Monte Carlo (MC) candidate sample pool which satisfies the requirement of variation coefficient of failure probability. It will lead to a reduction in the calculation efficiency of reliability analysis. To avoid this defect, a new method for determining the optimal size of the MC candidate sample pool is proposed, and a new structural reliability analysis method combining polynomial chaos-based Kriging model (PC-Kriging) with adaptive sampling region is also proposed (PCK-ASR). Firstly, based on the lower limit of the confidence interval, a new method for estimating the optimal size of the MC candidate sample pool is proposed. Secondly, based on the upper limit of the confidence interval, an adaptive sampling region strategy similar to the radial centralized sampling method is developed. Then, the k-means++ clustering technique and the learning function LIF are used to complete the adaptive design of experiments (DoE). Finally, the effectiveness and accuracy of the PCK-ASR method are verified by three numerical examples and one practical engineering example.

• 한국소음진동공학회논문집
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• 제14권9호
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• pp.819-826
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• 2004

A multi-step optimum strategy for the selection of the locations and directions of strain gauges is proposed in this paper to capture at best the modal response of blade in a series of modes on fan blades. It is consist of three steps including two pass reduction step, genetic algorithm and fine optimization to find the locations-directions of strain gauges. The optimization is based upon the maximum signal-to-noise ratio(SNR) of measured strain values with respect to the inherent system measurement noise, the mispositioning of the gauge in location and gauge failure. Optimal gauge positions for a fan blade is analyzed to prove the effectiveness of the multi-step optimum methodology and to investigate the effects of the considering parameters such as the mispositioning level, the probability of gauge failure, and the number of gauges on the optimal strain gauge position.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2004년도 춘계공동학술대회 논문집
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• pp.607-610
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• 2004

It is still not sufficient for the famous embedded software test methods such as Finite State Machine, Software Cost Reduction and model coverage based test case generation, to pinpoint where bugs hang around and to figure out what makes the bugs. A new approach to ameliorate the drawbacks is proposed in this paper. In the approach, we define a generic model for embedded software. And we also define failure mechanism for embedded software, and a way to generate test cases based on it.

• 품질경영학회지
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• 제34권4호
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• pp.78-92
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• 2006

While many services appear, it are performed in the various researches about a service. Among them, as to the basic reason for measuring the service level, in order to find out the strategy improving service quality. But the method for measuring quality of services up to date was unable to make it enough the role. This research tried to propose the approach systematically analyzing the human errors in order to improve service quality about the call center which utilizes the information technology. In fact, the human errors was found in the customer contact point in which the actual service is delivered. An interaction between the element for comprising call service was classified into 3 while defining the human error as 3 group. Moreover, the process where a service is delivered was classified according to 5 step and the generated error was measured in each step. The implication of this research looks at the service failure and dissatisfaction as the occurrence of the human errors and illustrates the service quality improvement as a correction or a reduction. This approach is used that service is materially easily understood and is formulated with the quality improvement strategy.

• 한국지진공학회논문집
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• 제27권6호
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• pp.293-301
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• 2023

Existing reinforced concrete buildings with seismically deficient details have premature failure under earthquake loads. The fiber-reinforced polymer column jacket enhances the lateral resisting capacities with additional confining pressures. This paper aims to quantify the retrofit effect varying the confinement and stiffness-related parameters under three earthquake scenarios and establish the retrofit strategy. The retrofit effects were estimated by comparing energy demands between non-retrofitted and retrofitted conditions. The retrofit design parameters are determined considering seismic hazard levels to maximize the retrofit effects. The critical parameters of the retrofit system were determined by the confinement-related parameters at moderate and high seismic levels and the stiffness-related parameters at low seismic levels.

• Geomechanics and Engineering
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• 제12권4호
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• pp.723-738
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• 2017

Rock is a heterogeneous material, which introduces complexity in the analysis of rock slopes, since both the existing discontinuities within the rock mass and the intact rock contribute to the degradation of strength. Rock failure is often catastrophic due to the brittle nature of the material, involving the sliding along structural planes and the fracturing of rock bridge. This paper proposes an advanced discretization method of rock mass based on block theory. An in-house software, GeoSMA-3D, has been developed to generate the discrete fracture network (DFN) model, considering both measured and artificial joints. Measured joints are obtained from the photogrammetry analysis on the excavation face. Statistical tools then facilitate to derive artificial joints within the rock mass. Key blocks are searched to provide guidance on potential reinforcement measures. The discretized blocky system is subsequently implemented into a discontinuous deformation analysis (DDA) code. Strength reduction technique is employed to analyze the stability of the slope, where the factor of safety can be obtained once excessive deformation of slope profile is observed. The combined analysis approach also provides the failure mode, which can be used to guide the choice of strengthening strategy if needed. Finally, an illustrated example is presented for the analysis of a rock slope of 20 m height inclined at $60^{\circ}$ using combined GeoSMA-3D and DDA calculation.