• Journal of the Society of Naval Architects of Korea
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• v.56 no.2
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• pp.161-167
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• 2019

In general, fatigue analysis is performed by using deterministic model to estimate the optimal parameters. However, the deterministic model is difficult to clearly describe the physical phenomena of fatigue failure that contains many uncertainty factors. With regard to this, efforts have been made in this research to compare with the deterministic model and the stochastic models. Firstly, One deterministic S-N curve was derived from ordinary least squares technique and two P-S-N curves were estimated through Bayesian-linear regression model and Markov-Chain Monte Carlo simulation. Secondly, the distribution of Long-term fatigue damage and fatigue life were predicted by using the parameters obtained from the three methodologies and the long-term stress distribution.

• Journal of Applied Reliability
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• v.11 no.2
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• pp.111-126
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• 2011

The clutch coil mounted on the automotive air conditioner is an important part which actuates the clutch to connect or disconnect the pulley and the compressor according to the climate control condition in an automobile. Here, it is generally required that the clutch coil should ensure the long term durability requirement, such as a warranty for the 10 years of field operation or 160,000 km driving, especially in a brand new item, and so forth. However, some difficulties have arisen in restoring its credibility, since domestic specifications for the part have not been yet unified. In order to ensure the reliability, test methods and assessment criteria should be standardized. Moreover, assessed lifetime under specific conditions and potential failure analysis would be important. In this study, lifetime test specifications for the clutch coil have been reviewed and methodological suggestions are provided to ensure reliability, utilizing a quality function deployment through the potential failure mode effect analysis.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.344-350
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• 2021

As the High Flux Advanced Neutron Application Reactor (HANARO) has been recently required to support new R&D relevant to future nuclear systems requiring a much higher neutron fluence, the development of irradiation capsule technology for long-term irradiation testing was performed in three steps (3, 5, 10 dpa). At first, several design improvements of a standard capsule were suggested based on a failure analysis of the capsule and successfully applied for irradiation testing at HANARO at up to eight reactor operation cycles equivalent to 3 dpa. Based on a schematic stress analysis of the vulnerable parts of the previous capsule, an optimized design of the capsule was made for 5 dpa irradiation. The newly designed capsule was safely out-pile tested up to 450 days, which was equivalent to 5 dpa irradiation in the reactor. The test results were submitted to the Reactor Safety Review Committee of HANARO and irradiation testing for 5 dpa was approved. The capsule was also successfully out-pile tested to evaluate the possibility of irradiation testing for 10 dpa. For a higher neutron fluence exceeding 10 dpa, new capsule technologies, including a new capsule that has a different bottom design and neutron flux boosting capsule, were also suggested.

• Journal of Chest Surgery
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• v.34 no.9
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• pp.686-691
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• 2001

Background: The Duromedics valve has been used in Korea since 1982, however, but there were no long term clinical results that have been reported. This paper presents the long term clinical results of Duromedics valve implanted in Seoul National University Hospital. Material and method: Between 1987, 23 patients underwnet cardiac valve replacement with Duromedics mechanical valve. There were 8 mitral valve replacements, 5 aortic valve replacements, one tricuspid valve replacement, 6 aortic and mitral valve replacements, and one mitral and tricuspid valve replacement. There were 12 men and 11 women. The mean age was 35$\pm$10(15~52) years. We evaluated the clinical performance of Duromedics cardiac prosthesis. Result: The early operative mortality was 4.3%(1/23) and the late morlatity was 4.3%(1/23). Causes of death were low cardiac output syndrome and structural valvular failure. The mean follow-up duration was 133$\pm$43(8~157) months. There were 3 reoperations. The causes of reoperations were thrombosis and structural failure and nonstructural valvular failure. The actuarial survival rate at 10 years was 90.9%. Conclusion: Although the number of patients was not sufficient for effective clinical study, the long term clinical results of Duromedics valve was relatively good and there was no structural defect in this mechanical valve. However, more research is needed in the future.

• Proceedings of the Korean Society for Quality Management Conference
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• 1998.11a
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• pp.287-292
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• 1998

As business looks towards the $21^{\st}$ century, a long-term strategy that focuses on global sourcing will be the vital factor in whether companies win or lose. At the same time, with electronic components, it is important to ensure stable quality and reliability, together with other important parameters. In order to achieve this, creating an effective mechanism of failure analysis and database management for electronic components is essential. The authors introduce the actual mechanism employed by NEC and explain the ideas and insight they have obtained from their experience.

• Structural Monitoring and Maintenance
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• v.2 no.4
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• pp.339-355
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• 2015

Corrosion of prestressed concrete structures is one of the main challenges that engineers face today. In response to this national need, this paper presents the results of a long-term project that aims at developing a structural health monitoring (SHM) technology for the nondestructive evaluation of prestressed structures. In this paper, the use of permanently installed low profile piezoelectric transducers (PZT) is proposed in order to record the acoustic emissions (AE) along the length of the strand. The results of an accelerated corrosion test are presented and k-means clustering is applied via principal component analysis (PCA) of AE features to provide an accurate diagnosis of the strand health. The proposed approach shows good correlation between acoustic emissions features and strand failure. Moreover, a clustering technique for the identification of false alarms is proposed.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.1
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• pp.41-47
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• 2020

The contribution of damage mechanisms to failure of steam turbine casing made of Cr-Mo-V steel was investigated. Creep-fatigue interaction on the HP side corner of turbine casing was revealed as the root cause of the catastrophic failure performed by metallurgical analysis. The steady-state pressure and transient thermal stress were analyzed based on the actual operating condition of the thermal plant. Damage of creep-fatigue interaction to crack initiation was evaluated with multiaxial effects. The contribution ratio of creep and fatigue to the crack initiation was estimated to 3:1. Temporary geometrical correct action with repair weld was executed. For long-term operation, design improvement of casing equipment for creep resistance should be needed.

• Journal of the Korean Society of Costume
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• v.63 no.3
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• pp.46-60
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• 2013

With a goal of establishing a marketing strategy which allows businesses to hold a dominant position in beauty service industry, this study has attempted to investigate causal relations among behavioral intentions by customer satisfaction once service recovery strategy is recovered depending on customers' emotional responses against service failure. In order to provide relevant data to make correct decisions during management and marketing planning so that better customer satisfaction can be achieved in the beauty service industry, the results of the previous studies on service failure and recovery strategy in the beauty service industry have been examined. Then after selecting i) the efforts to recover service failure, ii) satisfaction after recovery and iii) behavioral intention after satisfaction as causal variables, the relation among these variables were verified using a structural equation model. As a result, an appropriate recovery strategy which is developed after service failure makes customers have positive behavioral intentions when customer satisfaction is achieved just as described in previous studies. Furthermore, it is a critical fact which helps businesses keep their customers in a mature market, where it is hard to attract new customers and create long-term profit. This study empirically supports information on how service failure and related variables occur in the beauty service industry. It is significant in that it has helped beauty service providers build service recovery-related strategies.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.167-178
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• 2003

Damage and overbreak of the remaining rock induced by blasting can not be avoided during tunnel construction which may result in either short-term or long-term tunnel instability. Therefore, in this paper, a methodology to take into account the effect of blast-induced damage in tunnel stability assessment is proposed. Dynamic numerical analysis was executed to evaluate damage and overbreak of the remaining rock for the most common blasting pattern in road tunnel. Rock damage was quantified by utilizing the damage variable factor which is adopted proposed in continuum damage mechanics. The damaged rock stiffness and the damaged failure criteria are used to consider the effect of rock damage in tunnel stability analysis. The damaged geological strength index of the damaged rock was newly proposed from the relationship between deformation modulus and geological strength index. Also the Hoek-Brown failure criteria of the damaged rock was obtained using the damaged geological strength index. Analysing the tunnel stability with the consideration of the blast-induced damage of remaining rock, it was found that the extend of plastic zone and deformation increased compared to the undamaged rock. Therefore the short-term or long-term tunnel stability will be threatened when the rock damage from blasting is ignored in the tunnel stability analysis.

• Geomechanics and Engineering
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• v.5 no.1
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• pp.37-55
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• 2013

An important issue in the design of soil-nailing systems, as long-term retaining walls, is to assess their stability during seismic events. As such, this study is aimed at simulating the dynamic behavior and failure pattern of nailed structures using two series of numerical analyses, namely dynamic time history and pseudo-static. These numerical simulations are performed using the Finite Difference Method (FDM). In order to consider the actual response of a soil-nailed structure, nonlinear soil behaviour, soil-structure interaction effects, bending resistance of structural elements and construction sequences have been considered in the analyses. The obtained results revealed the efficiency of both analysis methods in simulating the seismic failure mechanism. The predicted failure pattern consists of two sliding blocks enclosed by three slip surfaces, whereby the bottom nails act as anchors and the other nails hold a semi-rigid soil mass. Moreover, it was realized that an increase in the length of the lowest nails is the most effective method to improve seismic stability of soil-nailed structures. Therefore, it is recommended to first estimate the nails pattern for static condition with the minimum required static safety factor. Then, the required seismic stability can be obtained through an increase in the length of the lowest nails. Moreover, placement of additional long nails among lowest nails in existing nailed structures can be considered as a simple retrofitting technique in seismic prone areas.