• The Transactions of the Korea Information Processing Society
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• v.3 no.7
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• pp.1917-1923
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• 1996

The reliability of the multiple-disk system is degraded as the number of disks are increased. In this paper, we find the reliability, in terms of MTTF (Mean Time To Failure)of the single-disk-failure-tolerant disk systems in which the distributions of repair times of failed disk are heterogeneous and general. Also, we derive thresholds of the design parameters such as the mean of life time and repair time, and we consider the cost minimization problem in the special cases under a linear cost structure and constraints to the life of the disk system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.428-434
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• 2020

The one-shot weapon system is destroyed after only one mission. So, the system requires high reliability. Guided missiles are one-shot weapon systems that have to be analyzed by storage reliability since they spend most of their life in storage. The analysis results depend on the model and the ratio of correct censored data. This study was conducted to propose a method to more accurately predict the future failure rate of Air force guided missiles. In the proposed method, the failure rate is predicted by both MTTF (Mean Time To Failure) and MTBF (Mean Time Between Failure) models and the model with a smaller error from the real failure rate is selected. Next, with the selected model, the ratio of correct censored data is selected to minimize the error between the predicted failure rate and the real failure rate. Based on real field data, the comparative result is determined and the result shows that the proposed sampling rate can predict the future failure rate more accurately.

• Journal of Korean Institute of Industrial Engineers
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• v.26 no.2
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• pp.128-135
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• 2000

This paper considers a consecutive k-out-of-n:F system when the failure of a component in the system induces higher failure rate of the preceding survivor. The reliability, mean time to failure(MTTF), and average failure number of a consecutive k-out-of-n:F system are obtained, when the failure of a component increases the failure rate of the survivor which is working just before the failed component. Then the optimal number of consecutive failed components to minimize this long run average cost rate can be obtained. An example is considered to calculate the reliability, MTTF and average failure number of the system. And two procedures that find the optimal number of consecutive failed components are studied. Then, various cases of system parameters are also studied.

• Journal of Applied Reliability
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• v.16 no.2
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• pp.162-170
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• 2016

Purpose: The purpose of this study was to analyze the failure modes of an auto transfer switch (ATS), determine the most common failure mechanisms, and iterate the design to improve reliability. Methods: We carried out failure mode and effect analysis (FMEA) to determine the failure modes and mechanisms. We identified the parts or modules that required improvement via two-stage quality function deployment based on FMEA, and improvements to reliability were monitored using the Gomperz growth model. Results: The main failure modes of the ATS were damage to, and deformation of, the stator / movable element due to repetitive movements. Five iterations of design modification were carried out, and the mean time to failure (MTTF) increased to 14,539 cycles, corresponding to 85% of the target MTTF. The Gompertz growth model indicates that the 10th iteration of design modification is expected to achieve the target MTTF. Conclusion: We improved the reliability of mechanical parts via failure mode analysis, and characterized the iterative improvements in the MTTF using the Gompertz growth model.

• Proceedings of the Safety Management and Science Conference
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• 2008.11a
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• pp.153-160
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• 2008

This paper presents the log likelihood function for integrated models for ALT such as exponential-general Eyring, Weibull-temperature and specific heat, lognormal-temperature and specific heat. Additionally this paper estimates the system reliability and mean time to failure(MTTF) for series, parallel, k of n, and standby system using ALT linkage parameter. Lastly this study designs three variable reliability acceptance sampling(RAS) plans such as type I, II censored test, sequential test by the use of integrated models for ALT.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.1
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• pp.109-119
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• 2013

This paper presents the design of the Safety Programmable Logic Controller (SPLC) used in the Nuclear Power Plants, an analysis of a reliability for the SPLC using a markov model. The architecture of the SPLC is designed to have the multiple modular redundancy composed of the Dual Modular Redundancy(DMR) and the Triple Modular Redundancy(TMR). The operating system of the SPLC is designed to have the non-preemptive state based scheduler and the supervisory task managing the sequential scheduling, timing of tasks, diagnostic and security. The data communication of the SPLC is designed to have the deterministic state based protocol, and is designed to satisfy the effective transmission capacity of 20Mbps. Using Markov model, the reliability of SPLC is analyzed, and assessed. To have the reasonable reliability such as the mean time to failure (MTTF) more than 10,000 hours, the failure rate of each SPLC module should be less than $2{\times}10^{-5}$/hour. When the fault coverage factor (FCF) is increased by 0.1, the MTTF is improved by about 4 months, thus to enhance the MTTF effectively, it is needed that the diagnostic ability of each SPLC module should be strengthened. Also as the result of comparison the SPLC and the existing safety grade PLCs, the reliability and MTTF of SPLC is up to 1.6-times and up to 22,000 hours better than the existing PLCs.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.194-202
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• 1998

This paper shows two models of the duplex system having a fault tolerant system characteristic used in airplane and railway system. The architecture of these systems is based on Mc68000, and we designed the single system, single duplex system, dual system and dual duplex system to evaluate the system characteristic. We calculate the failure rate of components using MIL-SPEC-2l7F and evaluate the reliability, avaliability, safety and MTTF(Mean Time To Failure) of the designed systems by Markov model. We choose our system depending on the developing system characteristic.

• Korean Journal of Computational Design and Engineering
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• v.20 no.1
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• pp.36-43
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• 2015

Recently, a number of evaluation studies on availability of plant were carried out. This study was conducted to verify of the reliability of a simulation with some variable such as configuration of process, failure probability density function and the number of iteration times for the natural gas liquefaction plant. The error rate of the KICT-RAM solution was evaluated as 0.03~1.79% compared with the result of the MAROS(commercial solution). And the error-rate change was observed in the range of 0.03~1.75 on the condition of the iteration times as 30, 100, 250. As a result the plant availability evaluation approach of KICT-RAM solution was verified as reasonable. However, the careful approach was required to use the solution because the error-rate increased according to iteration times change.

• Journal of Korean Society for Quality Management
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• v.10 no.2
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• pp.18-24
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• 1982

This paper estimates the reliability & mean time to failure (MTIF) of a cyclic or acyclic network system by the Monte-Carlo simulation method. Estimates of MTTF and Reliability become difficult as the complexity of a system increases. The method in this paper finds all simple paths from the given network, and then simulates the reliability of the required time and MTFF by using these paths. Life-times of the components in a network follow some probability distributions (Exponential, Weibull, Normal, Lognormal, etc.). The method, written in Level II. Basic Language, is validated for some simple examples and then estimates the reliability and MTFF of some cyclic network system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.44-49
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• 2021

Recently, infrared (IR) and near-infrared (NIR) light-emitting diodes (LEDs) were widely used for home medical applications owing to its low output power and wide exposed area for curing. For deep penetration of the light under the skin, multiple LEDs with wavelengths of 700~10,000 nm were located on a flexible printed circuit board. When multiple wavelengths of LEDs were soldered on a circuit board, the lifetime of LED module highly depends on LEDs with a short lifetime. The mean time to failure (MTTF) was able to calculate with the experimental results under high temperature and the Arrhenius model. The results of this study could help companies to approve the warranty of LED modules and its product.