• Journal of Applied Reliability
• /
• v.17 no.3
• /
• pp.246-255
• /
• 2017

Purpose: This study proposes the optimal PM (preventive maintenance) policy of leased equipment for lessee's decision-making using two types of reliability condition. Methods: We consider reliability threshold based PM model. Equipment reliability is estimated and used as condition variable. The effect of repair for maintenance is imperfect and represented by age reduction factor. Results: We provide two PM policies. Policy 1 is focused on minimized total cost. This policy guarantees reliability threshold until last maintenance action. Policy 2 focus on maintaining reliability threshold during leased period. The proposed approach provides optimal reliability threshold under number of PM. Through result, we finally construct decision-making process for lessee using reliability threshold and end of reliability. Conclusion: This study provides two PM policy for lessee's decision-making. Through numerical example, we get a result of optimal reliability threshold, number of PM, optimum alternative under lessee's reliability condition.

• Journal of Energy Engineering
• /
• v.8 no.4
• /
• pp.505-511
• /
• 1999

One of the major challenges confronting a multiservice electric utility is the establishment of the right prices, for its services. The key objectives of particular pricing schemes are reasonableness of company earnings. Economic efficiency, the responsiveness of supply and of the allocation of sources to the desires of consumers, and maintenance of some degree of competition. This paper proposes a value-based pricing mechanism amenable to the current deregulation situation in electricity market allowing service differentiation. The proposed pricing mechanism can be implemented ina nodal auction model, and can also be applied to direct load control.

• The Korean Journal of Applied Statistics
• /
• v.23 no.3
• /
• pp.573-584
• /
• 2010

This paper considers the differences in the software execution environments in the testing phase and the operational phase to determine the optimal release time and warranty period of software systems. We formulate equations for the total expected software cost until the end of the software life cycle based on the NHPP. In addition, we derive the optimal release time that minimizes the total expected software cost for an imperfect debugging software reliability model. Finally, we analyze the sensitivity of the optimal testing and maintenance design related to variation of the cost model parameters based on the fault data observed in the actual testing process, and discuss the quantitative properties of the proposed model.

• Communications for Statistical Applications and Methods
• /
• v.13 no.1
• /
• pp.191-204
• /
• 2006

This paper develops a Bayesian method to derive the optimal sequential preventive maintenance(PM) policy by determining the PM schedules which minimize the mean cost rate. Such PM schedules are derived based on a general sequential imperfect PM model proposed by Lin, Zuo and Yam(2000) and may have unequal length of PM intervals. To apply the Bayesian approach in this problem, we assume that the failure times follow a Weibull distribution and consider some appropriate prior distributions for the scale and shape parameters of the Weibull model. The solution is proved to be finite and unique under some mild conditions. Numerical examples for the proposed optimal sequential PM policy are presented for illustrative purposes.

• Proceedings of the Korean Reliability Society Conference
• /
• 2005.06a
• /
• pp.131-137
• /
• 2005

In this paper, we propose a Bayesian approach to determine the adaptive preventive maintenance(PM) policy for a general sequential imperfect PM model proposed by Lin, Zuo and Yam(2000) that PM not only reduces the effective age of the system but also changes the hazard rate function. Assuming that the failure times follow Weibull distribution, we adopt a Bayesian approach to update unknown parameters and determine the Bayesian optimal sequential PM policies. Finally, numerical examples of the optimal adaptive PM policy are presented for illustrative purposes.

• Journal of Korean Society for Quality Management
• /
• v.47 no.1
• /
• pp.87-96
• /
• 2019

Purpose: The purpose of this paper is to determine an optimal production time for economic production quantity model with preventive maintenance and random defective rate as the function of a machinery deteriorates. Methods: If a machinery shifts from "in-control" state to "out-of-control" state, a proportion of defective items being produced increases. It is assumed that time to state shift is a random variable and follows an arbitrary distribution. The elapsed time until process shift decreases stochastically as a production cycle repeats and quasi-renewal process is used to implement for production facilities to deteriorate. Results: When the exponential parameter for exponential distribution increases, the optimal production time increases. When Weibull distribution is considered, the optimal production time is closely affected by the shape parameter of Weibull distribution. Conclusion: A mathematical model is suggested to find optimal production time and optimal number of production cycles and numerical examples are implemented to validate the patterns for changes of optimal times under different parameters assumptions. The real application is implemented using the proposed approach.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.05a
• /
• pp.171-174
• /
• 2007

During last 30 years, Korea economy has grown so fast and many leading-edge technologies ware introduced from the advanced countries. but this fast growth inevitably produced imperfect completion of infrastructures and caused man-made catastrophes like Sungsu Bridge and Sampoong Department Store. After the incidents, Korea Government and National Assembly established "The Special Law for Safety Maintenance of Infrastructures". According to this law, most of infrastructures must be inspected periodically. During last 10 years after the establishment of the law, many infrastructures were improved and the quality of construction was upgraded. However, important and weak-to-disaster infrastructures need to be watched continuously. Many monitoring technologies were developed and tested in the field. In this paper, the new research project "Establishment of Testbed of Safety Management Network for Main Infrastructures", funded by government, was introduced.

• Journal of Electrical Engineering and Technology
• /
• v.4 no.1
• /
• pp.49-54
• /
• 2009

One of the major challenges confronting a multiservice electric utility is the establishment of the right prices for its services. The key objectives of particular pricing schemes are reasonableness of company earnings, economic efficiency, the responsiveness of supply and of the allocation of sources to the desires of consumers, and maintenance of some degree of competition. This paper proposes a value-based pricing mechanism amenable to the current deregulation situation in electricity market allowing service differentiation. The proposed pricing mechanism can be implemented in a nodal auction model, and can also be applied to direct load control.

• The Journal of Korean Medicine
• /
• v.19 no.2
• /
• pp.17-35
• /
• 1998

Medication used during pregnancy may affect the growth of fetus and maintenance of pregnancy so that it may cause fetal deformity or abortion. Before 1940 it was recognized that only genetic factor could affect the incidence of fetal deformity and the teratogen was protected by placenta barrier. But since the report that Thalidomide caused phocomelia was announced in l962 and 1962, it was acknowledged that the placenta barrier was imperfect. In oriental medical care, there were so many prescription used during pregnancy for nausea, threatened abortion, recurrent spontaneous abortion and it was acknowledged that those medication did not harm both maternity and fetus. Most of them are composed of the material that was not classified as prohibition during pregnancy. But we thought that it should be demonstrated through objective methods that these materials do not affect the incidence of fetal deformity or abortion and have the effect of preventing abortion and maintenance of pregnancy. As the first step of that study we researched 78 prescription and each materials, their kinds and using frequency, used for illness and symptoms during pregnancy written in Dongeuibokam(東醫寶鑑) so that we got to know the tendency about what materials are used for each illness and symptoms.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.13 no.7
• /
• pp.636-641
• /
• 2000

The purpose of this study is assessing the characteristics of surface aging and recovery of hydrophobicity for silicone rubber which takes a great interest as outdoor insulation recently subjected to the combined stressed of salt fog and AC power. The methods for assessing are contact angle ATR-FRIR, AFM and XRD. In addition salt fog method is adopted as the artificial contamination experiment and AC power is applied 24 hour on and 24 hour off repeatedly for 5 cycles. The results suggest that degraded surface was more rough than virgin but was restored water repellency through the off cycle. It was due to not only the formation of fractal surface but also maintenance of hydrophobic surface by diffusion of low molecular oil. Although surface recovers initial hydropohbicity there are possibilities of decreasing electrical performance due to irreversable changes such as depolymerization of surface and loss of filler particles. This fact is confirmed by surface conductivity measurement showing that the degradation is significant and the recovery of hydrophobicity is imperfect as the energized cycle increases.