• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1705-1711
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• 1991

On-line fault detection and diagnosis has an increasing interest in a chemical process industry, especially for a process control and automation. The chemical process needs an intelligent operation-aided workstation which can do such tasks as process monitoring, fault detection, fault diagnosis and action guidance in semiautomatic mode. These tasks can increase the performance of a process operation and give merits in economics, safety and reliability. Aiming these tasks, series of researches have been done in our lab. Main results from these researches are building appropriate knowledge representation models and a diagnosis mechanism for fault detection and diagnosis in a chemical process. The knowledge representation schemes developed in our previous research, the symptom tree model and the fault-consequence digraph, showed the effectiveness and the usefulness in a real-time application, of the process diagnosis, especially in large and complex plants. However in our previous approach, the diagnosis speed is its demerit in spite of its merits of high resolution, mainly due to using two knowledge models complementarily. In our current study, new knowledge representation scheme is developed which integrates the previous two knowledge models, the symptom tree and the fault-consequence digraph, into one. This new model is constructed using a material balance, energy balance, momentum balance and equipment constraints. Controller related constraints are included in this new model, which possesses merits of the two previous models. This new integrated model will be tested and verified by the real-time application in a BTX process or a crude unit process. The reliability and flexibility will be greatly enhanced compared to the previous model in spite of the low diagnosis speed. Nexpert Object for the expert system shell and SUN4 workstation for the hardware platform are used. TCP/IP for a communication protocol and interfacing to a dynamic simulator, SPEEDUP, for a dynamic data generation are being studied.

• 정보보호학회논문지
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• 제24권3호
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• pp.453-460
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• 2014

오류주입공격(Fault Injection Attack)은 하드웨어적 또는 소프트웨어적으로 구현된 암호칩에 인위적으로 오류를 주입 또는 발생시켜 암호 알고리즘 동작/수행을 방해함으로써 칩에 내장된 정보를 찾아내는 공격으로, 이 중 레이저를 이용한 오류주입공격은 특히 성공적인 것으로 입증된 바 있다. 본 논문에서는 기존의 플래쉬 펌프 방식의 레이저와 광섬유 레이저 모델을 병렬 결합한 이중모드 레이저 방식으로 개선된 레이저 프루빙 시스템을 제안하였다. 제안된 방법은 에너지 출력은 높으나 주파수 반복률이 낮아 오류주입공격 실험에 적합하지 않은 기존의 플래쉬 펌프 방식 레이저를 레이저 절단용으로 활용하고, 추가로 별도의 오류주입을 위한 고주파 반복률을 갖는 레이저를 단순 병렬 결합시키는 방법이다. 오류주입을 위해 결합된 제 2의 신규 레이저는 반도체 레이저와 광섬유 레이저를 선택하여 두 가지 시스템을 설계하였으며, 이에 따른 장 단점을 비교분석하였다.

• 한국가스학회지
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• 제23권4호
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• pp.19-27
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• 2019

세계 환경규제가 강화되면서 액화천연가스의 사용량이 지속해서 증가하고 있다. 안정적이고 효율적인 액화천연가스 생산을 위해서는 운전 조건을 세분화하여 감시하는 시스템 구축이 필수적이다. 본 연구에서는 천연가스 액화플랜트 성분 분리공정을 해석하여 구축한 동적 모델 데이터를 대상으로 다중 모드 감시시스템 개발 방법을 제안하였다. 먼저 전체 정상 데이터를 주성분분석과 k-평균 군집화 방법론을 사용하여 다중 정상 운전 모델로 구분하였다. 그 다음, 새로운 데이터 값을 k-최근접 알고리즘으로 구축된 다중 정상 모드와 매칭하였다. 마지막으로, 다중 모드 주성분분석 감시 기법을 통해 공정 데이터의 이상 여부를 판별하였다. 제시된 방법론은 45가지 이상경우에 적용하였고, 기본 주성분분석 방법론과 단변수 감시 방법론과의 비교를 통해 속도와 정확도 지표에서 평균 약 5~10%이상 우수함을 입증하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.57-61
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• 2015

A Superconducting Fault Current Limiter is an electric power device which limits the fault current immediately in a power grid. The SFCL must be cooled to below the critical temperature of high temperature superconductor modules. In general, they are submerged in sub-cooled liquid nitrogen for their stable thermal characteristics. To cool and maintain the target temperature and pressure of the sub-cooled liquid nitrogen, the cryogenic cooling system should be designed well with a cryocooler and coolant circulation devices. The pressure of the cryostat for the SFCL should be pressurized to suppress the generation of nitrogen bubbles in quench mode of the SFCL. In this study, we tested the performance of the cooling system for the prototype 154 kV SFCL, which consist of a Stirling cryocooler, a subcooling cryostat, a pressure builder and a main cryostat for the SFCL module, to verify the design of the cooling system and the electric performance of the SFCL. The normal operation condition of the main cryostat is 71 K and 500 kPa. This paper presents tests results of the overall cooling system.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1529-1532
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• 2007

Failure Mode, Effects, and Criticality Analysis (FMECA) is an extension of FMEA which includes a criticality analysis. The criticality analysis is used to chart the probability of failure modes against the severity of their consequences. The result highlights failure modes with relatively high probability and severity of consequences, allowing remedial effort to be directed where it will produce the greatest value. However, there are several limitations. Measuring severity of failure consequences is subjective and linguistic. Since The result of FMECA only gives qualitative and quantitative informations, it should be re-analysed to prioritize critical units. Fuzzy set theory has been introduced by Lotfi A. Zadeh (1965). It has extended the classical set theory dramatically. Based on fuzzy set theory, fuzzy logic has been developed employing human reasoning process. IF-THEN fuzzy rule based assessment approach can model the expert's decision logic appropriately. Fault tree analysis (FTA) is one of most common fault modeling techniques. It is widely used in many fields practically. In this paper, a simple fault tree analysis is proposed to measure the severity of components. Fuzzy rule based assessment method interprets linguistic variables for determination of critical unit priorities. An rail-way transforming system is analysed to describe the proposed method.

• Coupled systems mechanics
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• 제5권2호
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• pp.101-126
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• 2016

Seismic structural fragility constitutes an important step for performance based seismic design. Lateral load-resisting structural members are often analyzed under one component base excitation, while the effect of bi-directional shaking is accounted per simplified rules. Fragility curves are constructed herein under real bi-directional excitation by a simple extension of the conventional Incremental Dynamic Analysis (IDA) under uni-directional shaking. Simple SODF systems, parametrically adjusted to different periods, are examined under a set of near-fault and far-fault excitations. Consideration of bi-directional interaction appears important for stiff systems. Further, the study indicates that the peak ground accelertaion, velocity and displacement (PGA, PGV and PGD) of accelerogram are relatively stable and efficient intensity measures for short, medium and long period systems respectively. '30%' combination rule seems to reasonably predict the fragility under bi-directional shaking at least for first mode dominated systems dealt herein up to a limit state of damage control.

• Nuclear Engineering and Technology
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• 제39권1호
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• pp.51-62
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• 2007

To efficiently design safety-critical systems such as nuclear power plants, with the requirement of high reliability, methodologies allowing for rigorous interactions between the synthesis and analysis processes have been proposed. This paper attempts to develop a reliability-centered design framework through an interactive process between Axiomatic Design (AD) and Fault Tree Analysis (FTA). Integrating AD and FTA into a single framework appears to be a viable solution, as they compliment each other with their unique advantages. AD provides a systematic synthesis tool while FTA is commonly used as a safety analysis tool. These methodologies build a design process that is less subjective, and they enable designers to develop insights that lead to solutions with improved reliability. Due to the nature of the two methodologies, the information involved in each process is complementary: a success tree versus a fault tree. Thus, at each step a system using AD is synthesized, and its reliability is then quantified using the FT derived from the AD synthesis process. The converted FT provides an opportunity to examine the completeness of the outcome from the synthesis process. This study presents an example of the design of a Containment Heat Removal System (CHRS). A case study illustrates the process of designing the CHRS with an interactive design framework focusing on the conversion of the AD process to FTA.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.386-403
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• 2016

The safety of nuclear power plants is analyzed by a probabilistic risk assessment, and the fault tree analysis is the most widely used method for a risk assessment with the event tree analysis. One of the well-known disadvantages of the fault tree is that drawing a fault tree for a complex system is a very cumbersome task. Thus, several graphical modeling methods have been proposed for the convenient and intuitive modeling of complex systems. In this paper, the reliability graph with general gates (RGGG) method, one of the intuitive graphical modeling methods based on Bayesian networks, is improved for the reliability analyses of dynamic systems that have various operation modes with time. A reliability matrix is proposed and it is explained how to utilize the reliability matrix in the RGGG for various cases of operation mode changes. The proposed RGGG with a reliability matrix provides a convenient and intuitive modeling of various operation modes of complex systems, and can also be utilized with dynamic nodes that analyze the failure sequences of subcomponents. The combinatorial use of a reliability matrix with dynamic nodes is illustrated through an application to a shutdown cooling system in a nuclear power plant.

• 한국정보과학회논문지:정보통신
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• 제36권4호
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• pp.339-350
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• 2009

무선 센서 네트워크에서 센서 노드의 한정된 배터리 자원은 네트워크 수명에 직접적인 영향을 끼친다. 따라서 불필요한 전력 소모를 줄이기 위해, 많은 경우 최소한의 센서 노드만을 활성 모드로 유지하고 나머지는 휴면 모드로 유지한다. 그러나 이러한 경우, 예상하지 못한 결함으로 인해 센서 노드가 감지 및 전송 기능을 수행하지 못하게 되면 네트워크 서비스를 안정적으로 제공할 수가 없다. 따라서 센서노드의 결함에도 불구하고 감지수준을 일정하게 유지하는 것은 신뢰성 있는 감지환경을 제공하는 데 있어 매우 중요하다. 본 논문에서는 센서 노드의 결함으로 인한 감지수준 저하의 문제를 효과적으로 극복하기 위해 FCP(Fault-tolerant Coverage Preserving) 기법을 제안한다. FCP 기법에서는 각 활성 노드에 대해 백업 노드 집합을 미리 선정하여, 활성 노드의 결함 시 결함 노드를 대신하도록 한다. 성능 평가 결과, FCP 기법이 기존 결함 허용 기법들에 비해 평균 87.2% 향상된 감지범위 보존 성능을 보일 뿐 아니라, 추가 백업 노드 수와 추가 제어 메시지 전송량 측면에서도 각각 평균 57.6%, 평균 99.5% 향상된 효율성을 제공함을 보였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1178-1179
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• 2008

This paper describes a modeling of fixed speed wind power generation system which comprise of wind turbine, generator and grid. The wind turbine is based on MOD-2, which is IEEE standard wind turbine, and includes a component using wind turbine characteristic equation. Fixed speed induction generator is directly connected to grid, so the variation of wind speed has effects on the electrical torque and electrical output power. Therefore the power control mode pitch control system is necessary for aerodynamic control of the blades. But the power control mode does not operate at the fault condition. So it is required some methods to control the rotor speed at transient state for stabilization of wind power system. In this paper, simulation model of a fixed speed wind power generation system based on the PSCAD/EMTDC is presented and implemented under the real weather conditions. Also, a new pitch control system is proposed to stabilize the wind power system at the fault condition. The validity of the stabilization method is demonstrated with the results produced through sets of simulation.