• Journal of the Korean Institute of Gas
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• v.22 no.6
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• pp.40-43
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• 2018

For pressure safety valves, open failure and close failure are partially dependent on each other. A method is proposed in this work that uses a Markov process model and a Weibull distribution model in order to construct a reliability model for two kinds of failure. A pressure safety valve model is obtained from a known open failure model, an induced close failure model, and a simultaneous failure model that reproduces recently reported inspection results. It is expected that the application of the proposed method can be expanded to quantitative risk assessment of various systems that have partially dependent multiple failure states.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.6
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• pp.731-741
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• 2013

CCTV inspection method has been used in Korea for more than 20 years, but there is no proper assessment system for sewer failure severity that considers the domestic circumstances. This study classified the defects caused by the overburden load of reinforced concrete sewer pipes depending on severity and developed defect code by analyzing the domestic CCTV inspection videos. The defect score was assigned to each defect code, and it was classified into 5 grades for the decision-making of repair and rehabilitation. The result of this study is expected to be useful for domestic CCTV inspectors to assess the sewer condition and helpful for managers to make a decision of repair and rehabilitation.

• Proceedings of the Korean Reliability Society Conference
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• 2004.07a
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• pp.227-232
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• 2004

The failure of geogrids can be defined as an excessive creep strain which causes the collapse of slopes and embankments. In this study, the accelerated creep tests were applied to two different types of polyester geogrids, at 75, 80, 85$^{\circ}C$ by applying 50% load of ultimate tensile strengths using a newly designed test equipment which is allowed the creep testing at higher temperatures. And then the creep curves were shifted and superposed in the time axis by applying time-temperature supposition principles. In predicting the lifetimes of geogrids, the underlying distribution for failure times were determined based on identification of the failure mechanism. The results indicate that the conventional procedures with the newly designed test equipment are shown to be effective in prediction of the lifetimes of geogrids with shorter test times. In addition, the predicted lifetimes of geogrids having different structures at various creep strains give guidelines for users to select the proper geogrids in the fields.

• 한국가스학회:학술대회논문집
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• 2003.10a
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• pp.37-42
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• 2003

• Journal of Welding and Joining
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• v.19 no.5
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• pp.466-473
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• 2001

• Journal of Applied Reliability
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• v.7 no.2
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• pp.89-100
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• 2007

For the certification of aircraft and part, it must be show the compliance with applicable requirements through system safety assessment. The safety assessment process should be planned and managed to provide the necessary assurance that all relevant failure conditions have been identified and that all significant combinations of failures which could cause those failure conditions have been considered. Complex systems, especially aircraft, should take into account any additional complexities and interdependencies which arise due to integration. In all cases involving integrated systems, the safety assessment process is of fundamental importance in establishing appropriate safety objectives for the system and determining that the implementation satisfies these objectives. This study review the safety assessment for the certification process of the aircraft engine system and analyze turbo-fan engine by fault analysis method for compliance with airworthiness requirement of aircraft engine system.

• Journal of Korean Society of Disaster and Security
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• v.7 no.1
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• pp.43-50
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• 2014

Based on the reliability theory, the risk assessment of steel beams is performed by the determination of failure probability. In the calculation, bending, shearing and combined (bending + shearing) modes are examined. The resistance and the loads on the beam are assumed to be normal distribution. To investigate the failure probability changes, total load applied at the mid span of beam is divided into 1 to 1 and 1 to 2 ratio and then these divided loads are placed on the trisected points on beam. The change of boundary conditions at beam ends are also included in the investigation. It shows that failure is governed by the combined mode for the present beams and the second order bound analysis of failure probability is not crucial. On the whole failure probability decreases with increasing end restraints at the beam ends with some exception.

• Fire Science and Engineering
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• v.30 no.5
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• pp.116-123
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• 2016

The quantitative risk assessment methods for thermal failure in targets were studied using fire modeling. To this end, Fire Dynamics Simulator (FDS), as a representative fire model, was used and the probabilities related to thermal damage to an electrical cable were evaluated according to the change in fire area inside a specific compartment. 'The maximum probability of exceeding the damage thresholds' adopted in a conservative point of view and 'the probability of failure' including the time to damage were compared. The probability of failure suggested in the present study could evaluate the quantitative fire risk more realistically, compared to the maximum probability of exceeding the damage thresholds with the assumption that thermal damage occurred the instant the target reached its minimum failure criteria in terms of the surface temperature and heat flux.

• Polymer(Korea)
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• v.32 no.5
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• pp.440-445
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• 2008

The failure mechanism and failure morphology of linear low density polyethylene (LLDPE) tubing under hydrostatic pressure were investigated. Microscopic observations using video microscope and scanning electron microscope indicate that the failure mode is a brittle fracture including cracks propagated from inner wall to outer wall. In addition, oxidation induction time and Fourier transform infrared spectroscopy results show the presence of exothermic peak and the increase in carbonyl index on the surface of fractured LLDPE tubing, due to thermal-degradation. An accelerated life test methodology and testing system for LLDPE tubing are developed using the relationship between stresses and life characteristics by means of thermal acceleration. Statistical approaches using the Arrhenius model and Weibull distribution are implemented to estimate the long-term life time of LLDPE tubing under hydrostatic pressure. Consequently, the long-term life time of LLDPE tubing at the operating temperature of $25^{\circ}C$ could be predicted and also be analyzed.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1149-1157
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• 2015

As a key part in the wind turbine system, the power electronic converter is proven to have high failure rates. At the same time, the failure of the wind power converter is becoming more unacceptable because of the quick growth in capacity, remote locations to reach, and strong impact to the power grid. As a result, the correct assessment of reliable performance for power electronics is a crucial and emerging need; the assessment is essential for design improvement, as well as for the extension of converter lifetime and reduction of energy cost. Unfortunately, there still exists a lack of suitable physic-of-failure based evaluation tools for a reliability assessment in power electronics. In this paper, an advanced tool structure which can acquire various reliability metrics of wind power converter is proposed. The tool is based on failure mechanisms in critical components of the system and mission profiles in wind turbines. Potential methodologies, challenges, and technology trends involved in this tool structure are also discussed. Finally, a simplified version of the tool is demonstrated on a wind power converter based on Double Fed Induction Generator system. With the proposed tool structure, more detailed information of reliability performances in a wind power converter can be obtained before the converter can actually fail in the field and many potential research topics can also be initiated.