• Journal of Korean Society for Quality Management
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• v.43 no.4
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• pp.471-488
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• 2015

Purpose: Double sampling $T^2$ chart is a useful tool for detecting a relatively small shift in process mean when the process is controlled by multiple variables. This paper finds the optimal design of the double sampling $T^2$ chart in both economical and statistical sense under Weibull failure model. Methods: The expected cost function is mathematically derived using recursive equation approach. The optimal designs are found using a genetic algorithm for numerical examples and compared to those of single sampling $T^2$ chart. Sensitivity analysis is performed to see the parameter effects. Results: The proposed design outperforms the optimal design of the single sampling $T^2$ chart in terms of the expected cost per unit time and Type-I error rate for all the numerical examples considered. Conclusion: Double sampling $T^2$ chart can be designed to satisfy both economic and statistical requirements under Weibull failure model and the resulting design is better than the single sampling counterpart.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11C
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• pp.85-93
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• 2001

In this paper, a path restoration method independent of failure location in all-optical networks is proposed and its wavelength requirements are calculated. In the proposed method, since a single backup wavelength is used for any link failure, a node can consist of only fixed wavelength transmitters, resulting in the levels node cost. Hence, restoration process can be triggered just after the failure detection, if combined with edge-disjoint path restoration method. This feature and the parallel cross-connection message transfer technique proposed in this paper make the restoration process faster. Also, it is shown the wavelength requirements in the proposed method are similar to the ones in the method using tunable backup wavelength, resulting in little increment for transmission cost.

• Transactions of Materials Processing
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• v.3 no.2
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• pp.147-155
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• 1994

The service life of tools in metal forming technology is to a large extent limited by wear and fatigue fracture of the active elements. This presents a basic request for tool cost minimization and reduction of extensive machine down time, caused by premature tool failure. Currents developments are dominated by steps to reduce the causes of tool failure. A main problem of forming technology remains the insufficient reliability of tools due to a large and incalculable life time fluctuation. Only a systematic investigation of the failure mechanisms and operational loading of tools can lead to future improvements in tool layout, that is optimization of tool usage.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.17 no.32
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• pp.221-226
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• 1994

Almost preventive maintenance policies assumed that the system after pm has failure rate as before pm with probability p and as good as new with probability 1-p. This paper considers the s-expected cost of the model with imperfect periodic preventive maintenance that increasing minimal repair costs at failure and obtains the optimum periodic preventive maintenance time. Numerical example are shown in which the failure time of the system has gamma distribution.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.761-774
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• 2009

To address the importance of geotechnical investigation, failure cases are taken up for consideration. One of them awaken this country to the importance of exact geotechnical investigation at the cost of many lives. Other failures were also occurred as the result of insufficient geotechnical investigation or missing some facts given by geotechnical investigation. A case which shows the unpredicted and unaccustomed settlement at bridge abutment introduced to emphasize the importance of exploring unknown nature of local soils.

• Journal of Korean Institute of Industrial Engineers
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• v.4 no.1
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• pp.1-3
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• 1978

This paper presents a model for determining the optimal number of minimal repairs before replacement. The basic concept parallels the periodic replacement model with minimal repair at failure introduced by Barlow and Hunter, only difference being the replacement signalled by the number of previous minimal repairs performed on the unit. In the case of Weibull distribution, which is widely used as a general failure distribution, the optimal solution could be obtained numerically and seems more cost effective compared to the Barlow and Hunter's Policy II.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.487-497
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• 2008

This paper addresses the Fault Monitoring System developed by Hyundai-Rotem based on the Mil-HDBK-2155 Failure Reporting, Analysis and Corrective Action System. The purpose of a FRACAS is to provide a documented history of any problems, failures, their associated corrective actions as well as detailing how and why each problem arose or failure occurred during the Warranty Period for Rolling Stock delivered by Hyundai-Rotem. The Fault Monitoring System can assess the reliability, availability and maintainability as well as can predict no. of failure at a time which can input to Life Cycle Cost.

• Korean Journal of Construction Engineering and Management
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• v.10 no.1
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• pp.78-90
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• 2009

Recently, operation of highway is the complex digital Infrastructure based on complicated IT. The application of IT is increasing more and more in digital Infrastructure. Though IT is very convenient, if unpredicted operating risk of highway occurs, widespread damage can be large. When operating risk of highway occurs, road users are out of smoothly-run service because of the operating interruption. This risk causes unpredicted operating management cost and additional maintenance cost. It will excess over the planned operating cost, which may leads to users's unsafety and operator's insolvency because of income loss. Until now, related studies to find out the risk are not sufficient. The purpose of this study is to suggest risk cost items and to estimate the reasonable risk cost by using simulation method in case of occurring the huge power failure at the operating digitalized highway. This study indicates the several plans to hedge against risk cost and the management of highway project. From now on, it will be used as basic data to confirm the soundness of operating system in Digital Infrastructure.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.74-78
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• 2002

In this study, We propose equations which can determine the number of sectionalizing switches for minimizing the outage and switch installation cost.

• Journal of Welding and Joining
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• v.29 no.4
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• pp.67-72
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• 2011

The proportion of the welding in the production process of machinery, buildings and marine structures is increasing and the joining are mainly conducted by butt and fillet weld. In the case of fillet weld, the shape of structures is complicated depending on the constraint on the geometry of the structures, therefore, the full penetration is mostly difficult. Accordingly, it is necessary to establish safe and economical criteria of design of the structures through the strength based on the penetration state of the fillet weld. Patterns of fatigue failure in cruciform fillet weld jont appear in the form of the root, toe and mixed failure. In the case of toe and mixed failure, the fatigue strength is higher than root failure. Therefore, we have to make the enough depth of penetration or perform the welding work through improving the fatigue strength of cruciform joints in welded structures. So it is necessary to optimize the penetrated depth in the range of the possible mixed failure and find the way in the cost-effective design to lessen the amount of the welding work.