• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.3
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• pp.654-662
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• 2016

As the number of gates and basic events in fault trees increases, it becomes difficult to calculate the exact probability of the top event. In order to overcome this difficulty the BDD methodology can be used to calculate the exact top event probability for small and medium size fault trees in short time. Fault trees are converted to BDD by using CUDD library functions and a failure path search algorithm is proposed to calculate the exact top event probability. The backward search algorithm is more efficient than the forward one in finding failure paths and in the calculation of the top event probability. This backward search algorithm can reduce searching time in the identification of disjoint failure paths from BDD and can be considered as an effective tool to find the cut sets and the minimal cut sets for the given fault trees.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.569-570
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• 2022

Failure situations occur frequently in the industry, and the existing 2D-based manual for this purpose is not intuitive to understand and it is difficult to immediately interact with maintenance experts. In this paper, we propose a technology that enables workers to perform maintenance in real time with the help of experts without restrictions in time and place based on augmented reality when a failure situation occurs at a remote location. A local virtual human-based expert diagnoses a failure situation based on an adapted panoramic image of a remote failure situation while wearing an HMD headset, and gives instructions to a remote operator. In addition, in an augmented reality (AR) environment in a remote location, for the interaction between the operator and the expert, the HMD's microphone is used to create the expert's hand as well as verbal communication. You can use to point or draw a picture. If this technology is used, it is possible to overcome the limitations of the existing 2D-based manual, and to provide assistance in performing maintenance smoothly remotely even if an expert does not directly visit a remote location.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.2
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• pp.128-139
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• 2017

Railway is one of the public transportation systems along with shipping and aviation. With the recent introduction of high speed train, its proportion is increasing rapidly, which results in the higher risk of catastrophic failures. The wheel bearing to support the train is one of the important components requiring higher reliability and safety in this aspect. Recently, many studies have been made under the name of prognostics and health management (PHM), for the purpose of fault diagnosis and failure prognosis of the bearing under operation. Among them, the most important step is to extract a feature that represents the fault status properly and is useful for accurate remaining life prediction. However, the conventional features have shown some limitations that make them less useful since they fluctuate over time even after the signal de-noising or do not show a distinct pattern of degradation which lack the monotonic trend over the cycles. In this study, a new method for feature extraction is proposed based on the observation of relative frequency energy shifting over the cycles, which is then converted into the feature using the information entropy. In order to demonstrate the method, traditional and new features are generated and compared using the bearing data named FEMTO which was provided by the FEMTO-ST institute for IEEE 2012 PHM Data Challenge competition.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.2
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• pp.135-140
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• 2016

Corrective controllers enable fault diagnosis and tolerance for various faults in asynchronous sequential circuits without resort to redesign. In this paper, we propose a static corrective controller in order to decrease the size of the controller. Compared with dynamic controllers, static controllers can be made using only combinational circuits, as they need no inner states. We address the existence condition and design procedures for static corrective controllers that overcome state transition faults. To show the validity and advantage, the proposed controller is applied to an SEU error counter implemented on FPGA.

• Journal of Intelligence and Information Systems
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• v.6 no.1
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• pp.51-64
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• 2000

사회 기간산업이라 할수 있는 전기, 가스 석유등의 대단위 산업설비들은 사고 발생시 대량의 인명, 재산 피해를 가져오기 때문에 고도의 안전관리 시스템 하에서 운용되고 있다 이러한 기존 산업설비들의 안전관리는 서로 분산, 독립적인 안전관리 시스템들을 사용하고 있다 분산, 독립적인 안전관리 시스템은 산업설비에 대한 사고나 고장발생시 대부분 사람에 의존한 상황처리 작업을 수행하게 된다. 즉 사고가 발생하면 다른 안전관리 시스템들을 확인하고 그 결과를 통합하는 과정을 거처 상황처리에 대한 대책을 세우게 된다 이러한 과정은 추가적인 인력소모와 시간소모가 발생하게 되고 상황처리자의 미숙한 상황처리로 인한 사고가 발생하기도 한다. 본논문에서는 이러한 독립 안전관리 시스템의 단점을 극복하고 사고 발생시 신속, 정확하고 효율적인 상황처리를 위해 개별적인 안전관리 모니터 시스템들을 통합하는 방법을 제시한다. 또한 기존의 독립적이고 단편적인 상황추론을 국복하고자 통합된 지식베이스와 모니터 시스템들의 실시간 자료에 근거한 블랙보드 기반의 제어지식을 이용하여 종합적인 상황추론을 수행한다. 이를 위하여 각 시설물들에 대한 고장진단 시스템을 포함하는 지능형 원격감시 제어 통합시스템을 제안한다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.149-155
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• 2004

This paper presents how to find proper operating points of FACTS devices to enhance the steady-state security level considering line contigency analysis. Three generic types of FACTS devices such as series controllers, shunt controllers, and series-shunt controllers are introduced and applied to moximize a security margin and to minimize security indices. Security indices related to line flows and bus voltages are utilized and minimized iteratively in this paper. Contingency analysis is performed to detect the most severe single line fault. In various load conditions, FACTS devices are tested to establish appropriate preventive or corrective action without generation re-dispatching or load shedding. The FACTS operation scheme is verified on the IEEE 57-bus system in a line-faulted contingency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.268-272
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• 2012

A propulsion controller for vehicles should be designed to overcome a sensor failure during a flight, and it is necessary to control the system properly at any circumstances. Therefore, the vehicles need to retain reliability on the sensor measurements by implementing extra sensors to replace the original control sensors in case of their failure. This paper presents the MIMO NARX model by simulation which substitutes measured values with estimated ones by the state estimation technique in case of a sensor failure in a turbojet engine. It is also presented that the NARX model can be adapted as an engine model in HILS equipments.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.12
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• pp.47-58
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• 1999

As the performance of processors improves, cache memories are used to overcome the difference of speed between processors and main memories. Generally cache memories are embedded and small sizes, fault coverage is a more important factor than test time in testing point of view. A new test algorithm and a new BIST architecture are developed to detect various fault models with a relatively small overhead. The new concurrent BIST architecture uses the comparator of cache management blocks as response analyzers for tag memories. A modified scan-chain is used for pre-testing of comparators which can reduce test clock cycles. In addition several boundary scan instructions are provided to control the internal test circuitries. The results show that the new algorithm can detect SAFs, AFs, TFs linked with CFs, CFins, CFids, SCFs, CFdyns and DRFs models with O(12N), where N is the memory size and the new BIST architecture has lower overhead than traditional architecture by about 11%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1B
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• pp.38-47
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• 2008

The system test was accomplished in delivery time for a suitable of various requirements at the software market. Especially, critical faults must be detected and removed for a close main functions and users against target system. In generally, proposed test methods are executed with a calendar time, not a competitive and effectiveness method as selective software testing. These methods are inapplicable to short term test or early system development stage. Moreover, it's accompanied by heavy cost. Overcoming of these problems, must attempted to new software test method role of core function in the system test. Selective software testing method is decided to mixing with the three-information such as a frequency, complexity of use scenario and fault impact. Using this information, searching a fatal error and usefully system test for an executed test scenario. In this paper, we have proposed new test method and verified testing results for the detection of critical faults or search a fatal errors with a system main function.

• Current Industrial and Technological Trends in Aerospace
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• v.8 no.1
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• pp.77-85
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• 2010

The current GPS constellation consists of 32 Block IIA/IIR/IIR-M satellites including 12 Block IIA satellites on service over 15 years. The satellites in poor space conditions may suffer from anomalies, especially influenced by aging atomic clocks which are of importance positioning and timing. Recently, the IGS Ultra-rapid predicted products have not shown acceptably high quality prediction performance because the Block IIA cesium clocks may be easily affected by various factors such as temperature and environment. The anomalies of aging clocks involve lower performance of positioning in the GPS applications. We, thus, describe satellite clock behaviors and anomalies induced by aging clocks and their detection technologies to avoid such anomalies.