• International Journal of Reliability and Applications
• /
• 제13권1호
• /
• pp.19-35
• /
• 2012

This paper presents an optimum design of step-stress partially accelerated life test (PALT) plan which allows the test condition to be changed from use to accelerated condition on the occurrence of fixed number of failures. Various life distribution models such as exponential, Weibull, log-logistic, Burr type-Xii, etc have been used in the literature to analyze the PALT data. The need of different life distribution models is necessitated as in the presence of a limited source of data as typically occurs with modern devices having high reliability, the use of correct life distribution model helps in preventing the choice of unnecessary and expensive planned replacements. Truncated distributions arise when sample selection is not possible in some sub-region of sample space. In this paper it is assumed that the lifetimes of the items follow Truncated Logistic distribution truncated at point zero since time to failure of an item cannot be negative. Optimum step-stress PALT plan that finds the optimal proportion of units failed at normal use condition is determined by using the D-optimality criterion. The method developed has been explained using a numerical example. Sensitivity analysis and comparative study have also been carried out.

• Smart Structures and Systems
• /
• 제22권2호
• /
• pp.151-159
• /
• 2018

Maintenance activities are regarded as a key part of the repairable deteriorating system because they maintain the equipment in good condition. In practice, many maintenance policies are used in engineering fields to reduce unexpected failures and slow down the deterioration of the system. However, in traditional maintenance policies, maintenance activities have often been assumed to be performed at the same time interval, which may result in higher operational costs and more system failures. Thus, this study presents two non-periodic preventive maintenance (PM) policies for repairable deteriorating systems, employing the failure rate of the system as a conditional variable. In the proposed PM models, the failure rate of the system was restored via the failure rate reduction factors after imperfect PM activities. Operational costs were also considered, which increased along with the operating time of the system and the frequency of PM activities to reflect the deterioration process of the system. A numerical example was provided to illustrate the proposed PM policy. The results showed that PM activities performed at a low failure rate threshold slowed down the degradation of the system and thus extended the system lifetime. Moreover, when the operational cost was considered in the proposed maintenance scheme, the system replacement was more cost-effective than frequent PM activities in the severely degraded system.

• Proceedings of the Korean Nuclear Society Conference
• /
• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
• /
• pp.264-270
• /
• 1998

This research broadens the prime concern of nuclear power plant operations from safe performance to both economic and safe performance. First emergency diesel generator is identified as one of main contributors for the lost plant availability through the review of plants forced outage records. The framework of an integrated architecture for performing modern on-line condition for operational availability improvement is configured in this work. For the development of the comprehensive sensor networks for complex target systems, an integrated methodology incorporating a structural hierarchy, a functional hierarchy, and a fault-system matrix is formulated. The second part of our research is development of intelligent diagnosis and maintenance advisory system, which employs Bayesian Belief networks (BBNs) as a high level reasoning tool incorporating inherent uncertainty use in probabilistic inference. Our prototype diagnosis algorithms are represented explicitly through topological symbols and links between them in a causal direction. As new evidence from sensor network development is entered into the model especially, our advisory of system provides operational advice concerning both availability and safety, so that the operator is able to determine the likely modes, diagnose the system state, locate root causes, and take the most advantageous action. Thereby, this advice improves operational availability

• Journal of the Society of Naval Architects of Korea
• /
• 제42권5호
• /
• pp.516-527
• /
• 2005

It has been estimated that up to $80\%$ of all marine accidents have human elements as a cause. Out of these, human elements of crew fatigue is one of the main causes of marine accident. Crew fatigue involves sleep, schedule, workload, off-time, alcohol, health and stress. With a ship handling simulator, the effect of alcohol on ship operational performance is studied for each 0.05 and 0.08 $\%$ blood alcohol concentrations(BAC). The main effect of alcohol was found that ship operational performance was significantly impaired by alcohol compared to that in the non-alcohol condition. The results of this research can be used as basic data to minimize marine accidents.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• 제48권8호
• /
• pp.587-590
• /
• 1999

In this study, it is the purpose to develope a cheap and compact $CO_2$ laser and to apply 60 Hz AC discharges as a new exciting source. An axial and water cooledtype was adopted as the laser mode. The laser performance characteristics as various parameters, such as gas pressure and discharge current, have been investigated. And the laser output and the efficiency of DC and 60 Hz AC discharge-exciting type have been measured and compared for the different input powers at the static operational pressure. As a result, the case of 60 Hz AC discharge-exciting type, the laser oscillation began at the condition of operational pressure 6 Torr and discharge current 5 mA. A maximum laser output of about 32 W was obtained at an operational pressure of 18 Toorr and a discharge current of 30 mA. In addition, the laser output was saturated from an operational pressure of about 14 Torr and a discharge current of about 20 mA. In this $CO_2$ laser, the laser output of 60 Hz AC discharge-exciting type was slightly higher than that of DC discharge-exciting type. And the laser efficiency was about 10 to 13% for the various operational pressures and the discharge currents.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 한국정밀공학회 2002년도 춘계학술대회 논문집
• /
• pp.873-876
• /
• 2002

This paper presents the effect of internal corrosion, external corrosion, material properties, operation condition, earthquake, traffic load and design thickness in pipeline on the failure prediction using a failure probability model. A nonlinear corrosion is used to represent the loss of pipe wall thickness with time. The effects of environmental, operational, and design random variables such as a pipe diameter, earthquake, fluid pressure, a corrosion rate, a material yield stress and a pipe thickness on the failure probability are systematically investigated using a failure probability model for the corrosion pipeline.

• Proceedings of the Korean Reliability Society Conference
• /
• 한국신뢰성학회 2002년도 정기학술대회
• /
• pp.403-410
• /
• 2002

This paper presents the effect of internal corrosion, external corrosion, material properties, operation condition, earthquake, traffic load and design thickness in pipeline on the failure prediction using a failure probability model. A nonlinear corrosion is used to represent the loss of pipe wall thickness with time. The effects of environmental, operational, and design random variables such as a pipe diameter, earthquake, fluid pressure, a corrosion rate, a material yield stress and a pipe thickness on the failure probability are systematically investigated using a failure probability model for the corrosion pipeline.

• Women's Health Nursing
• /
• 제16권4호
• /
• pp.381-389
• /
• 2010

Purpose: The purpose of this study was to analyze the concept seogueulpeum, in order to give a operational definition of middle-aged women's seogueulpeum. Methods: Walker and Avant's methods for concept analysis was used. Results: The defining attributes of seogueulpeum identified in this study were 1) time, 2) negativity, 3) vagueness, 4) passivity, 5) individuality. The antecedents of seogueulpeum were 1) a problematic condition, 2) past event, experiences for the problematic condition, and 3) interaction between the problematic condition and past event, experiences. The consequences of seogueulpeum included 1) to get worse for the problematic condition, 2) passive or active management for the problematic condition. Conclusion: Although further studies are required to refine the diverse attributes of the concept of seogueulpeum, according to this concept analysis of seogueulpeum, this study contribute to explain psychological health of middle-aged women. In addition to develop the adequate interventions decreasing seogueulpeum with aging in women is needed.

• Journal of the Korean Society of Safety
• /
• 제9권1호
• /
• pp.40-47
• /
• 1994

This study is conducted for both examination of a possiblity of danger and investigation of operational condition of selected 120 companies, to establish the safety standard of workplace hazards.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 한국소음진동공학회 2014년도 추계학술대회 논문집
• /
• pp.503-504
• /
• 2014