• Journal of Power Electronics
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• v.8 no.1
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• pp.101-107
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• 2008

In this paper, the features extracted from vibration time signals are used to detect the bearing fault condition. The decision tree is applied to diagnose the bearing status, which has the benefits of being an expert system that is based on knowledge history and is simple to understand. This paper also suggests a genetic algorithm (GA) as a method to reduce the number of features. In order to show the potentials of this method in both aspects of accuracy and simplicity, the reduced-feature decision tree is compared with the non reduced-feature decision tree and the PCA-based decision tree.

• Journal of Korean Institute of Industrial Engineers
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• v.22 no.1
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• pp.129-139
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• 1996

Fault tree analysis is NP-hard problem. In this paper, we present a method which reduces size of the fault tree by eliminating the irrelevant events. Irrelevant event is the event which has no contribution to the system failure. In a fault tree, the irrelevant events occur due to the existence of the replicated events. By investigating the structure of the replicated events we establish the conditions which characterize the irrelevant events. Based on these conditions we present the computational algorithm which eliminate the irrelevant events. Complexity of the algorithm is shown to be polynomial and so, this algorithm can be utilized efficiently in FTA.

• Nuclear Engineering and Technology
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• v.37 no.3
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• pp.259-264
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• 2005

This paper presents a vital area identification (VAI) method based on the current fault tree analysis (FTA) and probabilistic safety assessment (PSA) techniques for the physical protection of nuclear power plants. A structured framework of a top event prevention set analysis (TEPA) application to the VAI of nuclear power plants is also delineated. One of the important processes for physical protection in a nuclear power plant is VAI that is a process for identifying areas containing nuclear materials, structures, systems or components (SSCs) to be protected from sabotage, which could directly or indirectly lead to core damage and unacceptable radiological consequences. A software VIP (Vital area Identification Package based on the PSA method) is being developed by KAERI for the VAI of nuclear power plants. Furthermore, the KAERI fault tree solver FTREX (Fault Tree Reliability Evaluation eXpert) is specialized for the VIP to generate the candidates of the vital areas. FTREX can generate numerous MCSs for a huge fault tree with the lowest truncation limit and all possible prevention sets.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.1
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• pp.123-133
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• 1998

In this paper, an algorithm of fault detection and diagnosis during operation of induction motors under the condition of various loads and rates is investigated. For this purpose, the spectrum pattern of input currents is used in monitoring the state of induction motors, and by clustering the spectrum pattern of input currents, the newly occurrence of spectrum patterns caused by faults are detected. For the diagnosis of the fault detected, a fuzzy fault tree is designed, and the fuzzy relation equation representing the relation between an induction motor fault and each fault type, is solved. The solution of the fuzzy relation equation shows the possibility of occurence of each fault. The results obtained are summarized as follows : (1) Using clustering algorithm by unsupervised learning, an on-line fault detection method unaffected by the characteristics of loads and rates is implemented, and the degree of dependency for experts during fault detection is reduced. (2) With the fuzzy fault tree, the fault diagnosis process become systematic and expandable to the whole system, and the diagnosis for sub-systems can be made as an object-oriented module.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.305-309
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• 1993

The application of fault tree technique to the analysis of compressor failure is considered. The techniques involve the decomposition of the system into a logic diagram or fault tree in whichcertain basic or primary events lead to a specified top event which signifiss the total failure of the system. The fault trees are used to obtain miniumal cut sets from whichthe modes of system failure and, hence the reliability for the top event can be calculated. The method of constructing fault trees and the subsequent estimation of reliability of the system is illustrated through a compressor failure. FTA is roved to be efficient to investigate the compressor fault train.

• Ocean Systems Engineering
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• v.9 no.3
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• pp.261-285
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• 2019

Nowadays in offshore industry there are emerging hazards with vague property such as act of terrorism, act of war, unforeseen natural disasters such as tsunami, etc. Therefore industry professionals such as offshore energy insurers, safety engineers and risk managers in order to determine the failure rates and frequencies for the potential hazards where there is no data available, they need to use an appropriate method to overcome this difficulty. Furthermore in conventional risk based analysis models such as when using a fault tree analysis, hazards with vague properties are normally waived and ignored. In other word in previous situations only a traditional probability based fault tree analysis could be implemented. To overcome this shortcoming fuzzy set theory is applied to fault tree analysis to combine the known and unknown data in which the pre-combined result will be determined under a fuzzy environment. This has been fulfilled by integration of a generic bow-tie based risk analysis model into the risk assessment phase of the Risk Management (RM) cycles as a backbone of the phase. For this reason Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) are used to analyse one of the significant risk factors associated in offshore terminals. This process will eventually help the insurers and risk managers in marine and offshore industries to investigate the potential hazards more in detail if there is vagueness. For this purpose a case study of offshore terminal while coinciding with the nature of the Caspian Sea was decided to be examined.

• KIPS Transactions on Software and Data Engineering
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• v.2 no.1
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• pp.7-18
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• 2013

These days, the teaching and learning system has been increasing for the rapid advancement of the information technologies. We can access education systems of good quality anytime, anywhere and we can use the individually personalized teaching and learning system depending on developing the wireless communication technology and the multimedia processing technology. The more the various systems develop, the more software security systems become important. There are a lot kind of fault analysis methods to evaluate software security systems. However, the only assessment method to evaluate software security system is not enough to analysis properly on account of the various types and characteristic of software systems by progressing information technology. Therefore, this paper proposes an integrative method of Fault Tree Analysis (FTA) and Fault Modes and Effect Analysis(FMEA) to evaluate the security of e-teaching and learning system as an illustration.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10b
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• pp.582-584
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• 1998

객체 지향 설계 명세를 대상으로한 시스템의 안전성에 대한 검사를 하여, 표(Table)조작에 기초한 검증법을 제안하였다[4]. 제안한 검증법에서는 전문 분야별로 준비된 안정성 기준(Safety Standard)과 노우하우(Knowhow)를 이용하여, 안전성에 관한 이벤트(Event)와 액션(Action)의 관계표를 작성하였다. 그러나, 많은 실제 개발 현장에서는 실제 존재하는 안전성 기준의 부족 등으로 인하여, 이러한 검증법의 기용이 어렵다는 문제점이 있다. 이에 본 논문에서는 신뢰성 분석의 한 방법인 FTA(Fault Tree Analysis)의 FT(Fault Tree)도를 이용한 안정성 체크리스트(Check list)를 작성하여, 이를 바탕으로 관계표를 작성하는 새로운 방법을 제안하고자 한다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.79-86
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• 1999

This paper aims to propose a method that helps maintenance engineers to evaluate the damage states of bridge systems by using a Fuzzy Fault Tree Analysis(FFTA). It may be stated that Fuzzy Fault Tree Analysis may be may useful for the systematic md rational condition and safety assessment for real bridge systems problems because the approach is able to effectively deal with all the related bridge system damages in terms of the linguistic variables that incorporate systematically experts experiences and subjective judgement.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.180-190
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• 1997

A new method in the fault tree analysis (FTA) for the reliability calculation is suggested. Two steps are necessary in traditional method in evaluation of the occurrence probability of top event in fault tree (FT). The first step is to find the minimal outsets, and the second one is to substitute the result into the poincare equation. In order to reduce the enormous computing time of this method, lots of rapid algorithms have been developed. Almost of all achievements were, however, based on the partial structural properties of FT. In this paper, the FT is transformed to a non-linear graph G which has the same minimal outsets of original n, and then the reliability is calculated using the domination theory. In this new method, the required number of equation terms are at most $2^n$ (n is node number of graph G), while $2^m$-1 (m is the number of minimal cutsets) calculation terms are required in the poincare equation in traditional method. Since m>>n in general. our new method reduces the calculation time significantly.