• Journal of Korean Society for Quality Management
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• v.29 no.3
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• pp.49-65
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• 2001

This paper presents new compromise ALT plan which is applied to situations that true relationship between stress and parameters is not known exactly. The assumed failure distribution of this study is one of location-scale family, i. e., exponential, Weibull, and lognormal distributions which have been ones of the popular choices of failure distributions. The method of applying the stress is constant, and the censoring mechanism is Type I censoring. Compared with existing compromise plans under true simple linear model in terms of statistical efficiency, the efficiency of new compromise plan is better than the corresponding other compromise ones in most cases. For case when true model is quadratic, this plan can be used without any severe loss in statistical efficiency. The proposed new compromise ALT plan is illustrated with a numerical example and sensitivity analyses are conducted to study effects of pre-estimates of design parameters.

• Journal of the Korea Society for Simulation
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• v.9 no.2
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• pp.75-87
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• 2000

In this paper, nonstationary multiple sampling plans are discussed which are difficult to solve by analytical method when there exists dependency between the sample data. The initial solution is found by the sequential sampling plan using the sequential probability ration test. The number of acceptance and rejection in each step of the multiple sampling plan are found by grouping the sequential sampling plan's solution initially. The optimal multiple sampling plans are found by simulation. Four search methods are developed U and the optimum sampling plans satisfying the Type I and Type ll error probabilities. The performance of the sampling plans is measured and their algorithms are also shown. To consider the nonstationary property of the dependent sampling plan, simulation method is used for finding the lot rejection and acceptance probability function. As a numerical example Markov chain model is inspected. Effects of the dependency factor and search methods are compared to analyze the sampling results by changing their parameters.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.21 no.45
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• pp.319-328
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• 1998

In this paper, the design of ALT(Accelerated Life Test) requires a sampling plan based on failure-censored(Type II censored) ALT with lognormal life distribution. Specially the environmental effect of products has been emphasized, so we considered the upper life limit as well as lower life limit in the ALT sampling plan. The optimal plan with a high stress and a low stress is used as test plan, and the total sample size for test and lot acceptability constant which minimize an asymptotic variance of maximum likelihood estimator of assumed model parameters and satisfy the given producer's risk and customer's risk are drawn out. These values can be acquired by means of the computer program that we coded for resolving the difficulty and complexity of calculation.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.27 no.4
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• pp.170-178
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• 2004

As quality becomes a primary leading factor of organizational success, various management strategies have been introduced to improve quality competitiveness. Quality competitiveness, however, is difficult to measure and numerous organizations are struggling to set realistic improvement objectives. The primary purpose of this research is to propose a systematic approach to help the practitioners develop an improvement plan for their organizational quality competitiveness. This approach employs DEA(Data Envelopment Analysis) to evaluate relative efficiency among companies which make efforts to improve their quality competitiveness. It presents an integer programming model to elicit an optimal improvement plan for meeting a target level. A decision support system is also developed for the managers to plan a sequential improvement plan based on both DEA model and the integer programming model.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.37-47
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• 2019

The study purposed to investigate the optimal location of core and offset outrigger system considering floor diaphragm. To accomplish this aim, a structure design of 70 stories building was performed by using MIDAS-Gen. And the leading factors of the analysis research were the slab stiffness, the stiffness of shear wall and the outrigger position in plan. Based on the analysis results, we analyzed and studied the influences of the shear wall stiffness and the slab stiffness on optimal location of core and offset outrigger considering floor diaphragm. The results of the analysis study indicated whether the slab stiffness, the stiffness of shear wall and the outrigger position in plan had an any impact on optimal location in outrigger system of tall building. Also the paper results can give help in getting the structural engineering materials for looking for the optimal position of outrigger system in the high-rise building.

• Journal of Korean Society for Quality Management
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• v.17 no.1
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• pp.89-106
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• 1989

For Weibull distributed lifetimes, this paper presents asymptotically optimal accelerated life test plans for practical applications under intermittent inspection and type-I censoring. Computational results show that the asymptotic variance of a low quantile at the design stress as optimal criterion is insensitive to the number of inspections at overstress levels. Sensitivity analyses indicate that optimal plans are robust enough to moderate departures of estimated failure probabilities at the design and high stresses as input parameters to plan accelerated life tests from their true values. Monte Carlo simulation for small sample study on optimal accelerated life test plans developed by the asymptotic maximum likelihood theory is conducted. Simulation results suggest that optimal plans are satisfactory for sample size in practice.

• Journal of Applied Reliability
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• v.18 no.2
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• pp.184-191
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• 2018

Purpose: The purpose of this study is to propose a method to calculate the optimal preventive maintenance cycle of radar used in the aviation weapon system of ROKAF. Methods: A hybrid model is used to estimate the optimal preventive maintenance cycle in a system that can perform condition based predictive maintenance (CBPM) through continuous diagnosis. The failure data of the radars operating in the military were used to calculate the reliability. Results: According to the research results, the reliability threshold of the radar began to decrease after 5 flights, and decreased rapidly after 12 flights. Since the second check, costs have continued to decline. Conclusion: A method is proposed to determine the cycle of optimal preventive maintenance of radar within operational budget through modeling results between reliability limit and cost for radar. The results can be used to determine the optimal preventive maintenance cycle and frequency of various avionics equipment.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.3
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• pp.117-126
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• 2009

Various dimensions of watershed structural/non-structural planning can be applied in comprehensive flood mitigation plan in a river basin. Especially structural counterplans have very broad and diverse nature as flood control facilities. It is not easy to find the optimum alternative to maximize the ability of a basin to reduce flood risk using a combination of structural counterplans. In addition, there is no standard for evaluating the performance of structural counterplans and for selecting optimal combination of them. This study focused on how to select the best alternative of a comprehensive watershed structural plan from various flood defense alternative candidates. By introducing an analytic hierarchy process, we would like to show how we decide the best alternative using standard worksheets developed in this study for economics and policy evaluation, and Expert Choice 11.5, which calculates weights for evaluation items. Based on the results from this study, we would like to suggest the best practice of a standardized watershed plan for flood protection.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.666-675
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• 2008

The IEEE 802.22 standard is being developed with the target of improving the efficiency of spectrum utilization and importing the new wireless communication service. The WRAN standard based on Cognitive Radio is being processed for sharing TV bands. In this paper, the efficient spectrum allocation scheme and the optimal power allocation scheme, Partial Constant Power Water Filling (PCPWF), are proposed to maximize the channel capacity and spectrum efficiency and minimize the interference between adjacent cells. And we maximize the system throughput and fairness by using proposed dynamic cell plan that efficiently allocates channel. The results of the simulations are presented to verify the utilization of our proposed scheme.

• Journal of Korean Society for Quality Management
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• v.18 no.2
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• pp.93-99
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• 1990

This paper considers the selection of process plans for a flexible manufacturing machine. Most of the planning models for the automated manufacturing systems are based on the assumption that for each part there is only one process plan available. This paper considers that for each part a number of different process plans are available, each of which may require specific types of tools. If the requisite tools are not on the machine, one or more tool switches must occur before the process plan can be processed. This paper develops an optimal algorithm of branch and bound method for the selection of process plans to minimize the number of tool switches.