• 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.

• Journal of Korean Society for Quality Management
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• v.20 no.2
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• pp.44-54
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• 1992

In conventional fault-tree analysis, the failure probabilities of components of a system are treated as exact values in estimating the failure probability of the top event. For the plant layout and systems of the products, however, it is often difficult to evaluate the failure probabilities of components from past occurences, because the environments of the systems change. Furthermore, it might be necessary to consider possible failure of components of the systems even if they have never failed before. In the paper, instead of the probability of failure, we propose the possibility of failure, viz, a fuzzy set defined in probability space. Thus, in this paper based on a fuzzy fault-tree model, the maximum possibility of system failure is determined from the possibility of failure of each component within the system according to the extension principle.

• Earthquakes and Structures
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• v.6 no.3
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• pp.281-300
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• 2014

This study proposes a scheme to design control parameters for a data center facility with a vibration controller on its top floor and a secondary isolation device with its own vibration controller designed to protect vibration-sensitive computer equipment. The aim is to reduce the effects of acceleration and drift from an earthquake on computer servers placed on the isolation device that must operate during a seismic event. A linear elastic model is constructed and the evaluation function of the linear quadratic Gaussian (LQG) control is formulated. The relationship between the control parameters and the responses is examined, and based on the observations, a control parameter design scheme is constructed to reduce the responses of both the building and the computer server effectively.

• Nuclear Engineering and Technology
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• v.15 no.1
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• pp.11-22
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• 1983

The reliability of the Chemical and Volume Control System has been analyzed in a pressurized water reactor. The boration failure was taken to be the top event for this reliability analysis. A detailed fault tree was constructed and the minimal cut sets were derived. It was computed that the unavailability of the Chemical and Volume Control System due to boration failure was 1.497$\times$10$^{-5}$ during plant operation. It was found that the reliability of boric acid transfer pumps were the most important factors in the availability of the Chemical and Volume Control System. As expected, human errors also introduce the high system unavilability.

• Nuclear Engineering and Technology
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• v.29 no.3
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• pp.211-217
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• 1997

Adverse effects caused by the surveillance test for the components of nuclear power plant involve plant transients, unnecessary wear, burden on licensee's time, and the radiation exposure to personnel along with the characteristics of each component. The optimization methodology of STI and AOT has been developed and applied to AFWPs of a reference plant. The approach proposed in this paper consist of the resole in minimal mean unavailability of the two-out-of-four system with adverse effects are analytically calculated for the example system. The surveillance testing strategy are given by the sequential test, the staggered test and the train staggered test which is a mined test scheme. In the system level, the sensitivity analyses for the STI and AOT, are performed for the measure of the system unavailability of the top event in the fault tree developed for the example system. This methodology may contribute to establishing the basis for the risk-based regulations.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.379-382
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• 2000

We designed a self-timed interface circuit for efficient communication in IP (Intellectual Property)-based system with high-speed self-timed FIFO and a set of self-timed event logic library with 0.25um CMOS technology. Optimized self-timed standard cell layouts and Verilog models are generated for top-down design methodology. A method for mitigating a design bottleneck when it comes to tolerate clock skew is described. With clock control method and FIFO, we implemented high-speed 32bit-interface chip for self-timed system, which generated maximum system clock is 2.2GHz. The size of the core is about 1.1mm x 1.1mm.

• Journal of the Korean Society of Safety
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• v.11 no.2
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• pp.52-59
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• 1996

This paper presents a new approach for assessing the dynamic reliability in a complex system such as a nuclear power plant. The method is applied to a dynamic analysis of the potential accident sequences which may occur during mid-loop operation. Mid-loop operation is defined as an operation to make RCS water level below the top of the flow area of the hot legs at the junction with the reactor vessel for repairs and maintenance of steam generators and reactor coolant pumps for a specific time. The Idea behind this approach consists of both the use of the concept of the performance achievement/requirement correlation and of a dynamic event tree generation method. The assessment of the system reliability depends on the determination of both the required performance distribution and the achieved performance distribution. The quantified correlation between requirement and achievement represents a comparison between two competing variables. It is demonstrated that this method is easily applicable and flexible in that it can be applied to any kind of dynamic reliability problem.

• 한국체육학회지인문사회과학편
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• v.55 no.5
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• pp.447-457
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• 2016

The purpose of this study is to check awareness of 'the phenomenon of women's alienation in Yon-Ko-Jeon' to women students, and improve the gender equality for Yon-Ko-Jeon through IPA(Importance Performance Analysis). For this study, 322 women undergraduates at Yonsei University and Korea University, from sophomore to senior students, are selected and asked to be surveyed. At first, a majority of women students from two universities didn't recognize the lack of women sports and athletes in Yon-Ko-Jeon. Moreover, they didn't think about women's alienation in Yon-Ko-Jeon as well as improvement for the issue seriously. It shows the life style of gender in the sport. Second, as a result of IPA, improvement plan of Yon-Ko-Jeon on gender equality shows it needs to reflect member's opinion and introduce women sports clubs first. Recently, the improvement for the Yon-Ko-Joen is the top priority because the event doesn't reflect member's opinion. Furthermore, it shows that Yon-Ko-Jeon needs to introduce the competition of women's club sports. These are what the event has to improve.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.205-216
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• 2024

Recently, seismic Probabilistic Safety Assessment (PSA) methods have been developed for process plants, such as gas plants, oil refineries, and chemical plants. The framework originated from the PSA of nuclear power plants, which aims to assess the risk of reactor core damage. The original PSA method was modified to adopt the characteristics of a process plant whose purpose is continuous operation without shutdown. Therefore, a fault tree, whose top event is shut down, was constructed and transformed into a Bayesian Network (BN), a probabilistic graph model, for efficient risk-informed decision-making. In this research, the fault tree-based BN from the previous research is further developed to consider the multi-hazard of earthquake-induced fire and explosion (EQ-induced F&E). For this purpose, an event tree describing the occurrence of fire and explosion from a release is first constructed and transformed into a BN. And then, this BN is connected to the previous BN model developed for seismic PSA. A virtual plot plan of a gas plant is introduced as a basis for the construction of the specific EQ-induced F&E BN to test the proposed BN framework. The paper demonstrates the method through two examples of risk-informed decision-making. In particular, the second example verifies how the proposed method can establish a repair and retrofit strategy when a shutdown occurs in a process plant.

• Journal of the Korean earth science society
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• v.36 no.3
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• pp.222-235
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• 2015

Samples were collected from both places including the coastal area within the height of 5 m above the mean sea level (msl) (DH) and the top of the coastal terrace of 10-15 m msl (KS) high in Gwangseungri, Gochanggun, Korea. To find the origin of the deposit in the coastal area, granulometric analysis and geochemical analysis were performed. The result showed that the DH samples were originated from the reddish soils overlaying weathered bedrock which presented gradual change of chemical composition from the bottom toward the top. Clay minerals were found from the DH samples. These results concluded that the DH samples were found as in-situ weathered materials. The KS samples were originated from the soil layer covering gravel layer at the foot slope of the hill along the coast. The KS samples contained different chemical compositions from the DH. It is inferred that some of this layer was disturbed or experienced the influx of foreign material. The particle size of the KS samples was different from those found on the beach. The particle size of lower parts of KS site was finer than that on the beach, but the particle size of middle part of the site was coarser than that on the beach. The sorting of the KS site was poorer than that on the beach. Thus, it is inferred that some parts of the layer were formed by short-lived high energy event rather than sustained and continuous action of tidal currents and/or waves. Analysis using an optically stimulated luminescence (OSL) method showed that the burial age of samples from KS site were found 0.65-0.71 ka. Though the characteristics of the sediment layer and forming event in this area should be further studied, it can be inferred that this sedimentary layer formed by coastal flooding with storm.