• IE interfaces
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• v.25 no.4
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• pp.405-415
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• 2012

The reliability performance measures for low and high or continuous demand modes of operation of safety instrumented systems(SISs) are examined and compared by analyzing the official definitions in IEC 61508 standard. This paper also presents a status of common cause factor(CCF) models used in IEC 61508 and problems relating CCF modelling are discussed and ideas to solve these ones are suggested. An example with mixed M-out-of-N architecture is carried out to illustrate the proposed methods.

• Nuclear Engineering and Technology
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• v.17 no.1
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• pp.53-67
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• 1985

The severe core meltdown accident, which is not included as a design basis accident, has high consequence and low probability of occurrence and turns out to be a major risk factor in the overall risk assessment. The physical mechanisms of containment failure in core meltdown accidents are identified as steam explosion, debris bed coolability, hydrogen burning, steam spike and concrete interaction. The state of technology review is made for each subtopic about the previous and current researches for better understanding of the phenomenon.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.5
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• pp.47-56
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• 2001

In order to assure the safety of NPP structures, margin of safety or conservatism is incorporated in each design step. Seismic risk evaluation of NPP structures is performed based on the realistic capacity and response of structure eliminated the safety margin and conservatism. In this study, the comparative study on the various evaluation methods of the inelastic energy absorption capacity was performed. The inelastic energy absorption capacity due to the nonlinear behavior of structures has significant effect on the results of seismic probabilistic risk assessment. And the comparison study of the HCLPF(high confidence of low probability of failure) values according to the inelastic energy absorption factors was performed. As a conclusion, the inelastic energy absorption factor of NPP containment structure is estimated about 1.5~1.75. It is essential to estimate the nonlinear behavior of structure and its ductility factor correctly for the seismic risk assessment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.739-746
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• 2004

The plastic deformation behavior of an aluminum alloy containing a particle and porosities was investigated at room temperature during equal channel angular pressing (ECAP). Finite element analysis by using ABAQUS shows that ECAP is a useful tool for eliminating residual porosity in the specimen, and more effective under friction condition. The simulation, however, shows considerably low density distributions for matrix near a particle at which many defects may occur during severe deformation. Finite element results of effective strains and deformed shapes for matrix with a particle were compared with theoretical calculations under simple shear stress. Also, based on the distribution of the maximum principal stress in the specimen, Weibull fracture probability was obtained for particle sizes and particle-coating layer materials. The probability was useful to predict the trend of more susceptible failure of a brittle coating layer than a particle without an interphase in metal matrix composites.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1157-1162
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• 2003

Behavior of aluminum alloy embedding a particle was investigated at room temperature under ECAP. Finite element analysis by using ABAQUS shows that ECAP is a useful tool for eliminating residual porosity in the specimen, and much more effective under friction condition. The simulation, however, shows considerably low density distributions for matrix near a particle at which rich defects may occur during severe deformation. Finite element results of effective strains and deformed shapes for matrix with a particle were compared with theoretical calculations under simple shear stress. Also, based on the distribution of the maximum principal stress in the specimen, Weibull fracture probability was obtained for particle sizes and particle-coating layer materials. The probability was useful to predict the trend of more susceptible failure of a brittle coating layer than a particle without an interphase in metal matrix composites.

• The Korean Journal of Financial Management
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• v.24 no.2
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• pp.113-145
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• 2007

In this paper, we examine whether the poor performance of distressed firms where banks take equity may occur due to agency problems in banks. By adopting the debt-equity swap, the bank can effectively postpone the occurrence of bad loans form the failure of the distressed firm. As a result, firms with more debt will be more likely to obtain debt-equity swap, regardless of their probabilities of revival. This is not because they are more profitable, but because they have more debt and thus it poses greater risk to the bank. We empirically look into these predictions with the data of 44 workout firms and find the following results. First, debt-equity swap appears to be more applicable especially when the distressed firms are large and when BIS of related banks is low. Specifically, the conditional probability of 'large firms' based on debt-equity swap is 65.52% and the conditional probability of 'bad banks' based on debt-equity swap is 75.86%. Also, as predicted, the performance of these debt-equity firms is poorer than that of non debt-equity firms. The conditional probability of 'large firms' based on posterior failure is 84.62% and the conditional probability of 'bad banks' based on posterior failure is 84.62%. This is consistent with our predictions and is also confirmed through results of the logit regression analysis. Second, when the restructuring is led by 'good banks', the performance of equity-swap firms is superior to that of non equity-swap firms. This result is consistent with that of James(1995). Hence, we can conclude that there may be some agency problems in restructuring distressed firm-especially when distressed firms are large and banks are bad. And these agency problems can reconcile the difference between James' results and Park, Lee, and Jang's.

• Tribology and Lubricants
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• v.30 no.4
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• pp.199-204
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• 2014

Various heat-treated and surface coating methods are used to mitigate abrasion in sliding machine parts. The most cost effective of these methods involves hard coatings such as diamond-like carbon (DLC). DLC has various advantages, including a high level of hardness, low coefficient of friction, and low wear rate. In practice, a supporting layer is generally inserted between the DLC layer and the steel substrate to improve the load carrying capacity. In this study, an indentation and sliding contact problem involving a small, hard, spherical particle and a DLC-coated steel surface is modeled and analyzed using a nonlinear finite element code, MARC, to investigate the influence of the supporting layer thickness on the coating characteristics and the related coating failure mechanisms. The results show that the amount of plastic deformation and the maximum principal stress decrease with an increase in the supporting layer thickness. However, the probability of the high tensile stress within the coating layer causing a crack is greatly increased. Therefore, in the case of DLC coating with a supporting layer, fatigue wear can be another important cause of coating layer failure, together with the generally well-known abrasive wear.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.103-111
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• 2014

In this study, the probabilistic internal pressure fragility analysis was performed by using the non-linear finite element analysis method. The target structure is one of the containment buildings of typical domestic pressurized water reactors(PWRs). The 3-dimensional finite element model of the containment building was developed with considering the large equipment hatches. To consider uncertainties in the material properties and structural capacities, we performed the sensitivity analysis of the ultimate pressure capacity with respect to the variation of four important uncertain parameters. The results of the sensitivity analysis were used to the selection of the probabilistic variables and the determination of their probabilistic parameters. To reflect the present condition of the tendon pre-stressing force, the data of the pre-stressing force acquired from the in-service inspections of tendon forces were used for the determination of the median value. Two failure modes(leak, rupture) were considered and their limit states were defined to assess the internal pressure fragility of target containment building. The internal pressure fragilities for each failure mode were evaluated in terms of median internal pressure capacity, high confidence low probability of failure(HCLPF) capacity, and fragility curves with respect to the confidence levels. The HCLPF capacity was 115.9 psig for leak failure mode, and 125.0 psig for rupture failure mode.

• Nuclear Engineering and Technology
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• v.41 no.2
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• pp.187-198
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• 2009

In this paper, three power ramp tests performed on high burn-up Re-crystallized Zircaloy2 - UO2 BWR fuel rods (56 to 63 MWd/kgU) within the SCIP project are simulated with METEOR and ALCYONE 3D. Two of the ramp tests are of staircase type up to Linear Heat Rates of 420 and 520 W/cm and with long holding periods. Failure of the 420 W/cm fuel rod was observed after 40 minutes. The third ramp test consisted of a more standard ramp test with a constant power rate of 80 W/cm/min up to 410 W/cm with a short holding time. The tests were first simulated with the METEOR 1D fuel rod code, which gave accurate results in terms of profilometry and fission gas releases. The behaviour of a fuel pellet fragment and of the cladding piece on top of it was then investigated with ALCYONE 3D. The size and the main characteristics of the ridges after base irradiation and power ramp testing were recovered. Finally, the failure criteria validated for PWR conditions and fuel rods with low-to-medium burn-ups were used to analyze the failure probability of the KKL rodlets during ramp testing.

• Journal of Ship and Ocean Technology
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• v.4 no.2
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• pp.38-57
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• 2000

This paper deals with reliability analysis of specially orthotropic plates subjected to transverse lateral pressure loads by using Monte Carlo simulation method. The plates are simply supported around their all edges and have a low short span to plate depth ratio with rectangular plate shapes. Various levels of reliability analyses of the plates are performed within the context of First-Ply-Failure(FPF) analysis such as ply-/laminate-level reliability analyse, failure tree analysis and sensitivity analysis of basic design variables to estimated plate reliabilities. In performing all these levels of reliability analyses, the followings are considered within the Monte Carlo simulation method: (1) input parameters to the strengths of the plates such as applied transverse lateral pressure loads, elastic moduli, geometric including plate thickness and ultimate strength values of the plates are treated as basic design variables following a normal probability distribution; (2) the mechanical responses of the plates are calculated by using simplified higher-order shear deformation theory which can predict the mechanical responses of thick laminated plates accurately; and (3) the limit state equations are derived from polynomial failure criteria for composite materials such as maximum stress, maximum strain, Tsai-Hill, Tsai-Wu and Hoffman.