• 한국국방경영분석학회지
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• 제22권2호
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• pp.215-226
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• 1996

The estimation of lifetimes are examined when the distribution of lifetimes are Weibull. It is assumed that, due to physical restrictions and/or economic requirements, the lifetimes are investigated only at certain time intervals during the test period with 'mixed replacement' experiment, even though it is well known that 'with replacement' experiment produces better accuracy than 'without replacement' one. The maximum likelihood estimators are derived through the iterative method like as Lawless(1982). Also Cramer-Rao lower bounds are found as the asymptotic variances of the estimates.

• 산업경영시스템학회지
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• 제45권3호
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• pp.78-89
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• 2022

The purpose of this study was to propose useful suggestion by analyzing preventive replacement policy under which there are minor and major failure. Here, major failure is defined as the failure of system which causes the system to stop working, however, the minor failure is defined as the situation in which the system is working but there exists inconvenience for the user to experience the degradation of performance. For this purpose, we formulated an expected cost rate as a function of periodic replacement time and the number of system update cycles. Then, using the probability and differentiation theory, we analyzed the cost rate function to find the optimal points for periodic replacement time and the number of system update cycles. Also, we present a numerical example to show how to apply our model to the real and practical situation in which even under the minor failure, the user of system is not willing to replace or repair the system immediately, instead he/she is willing to defer the repair or replacement until the periodic or preventive replacement time. Optimal preventive replacement timing using two variables, which are periodic replacement time and the number of system update cycles, is provided and the effects of those variables on the cost are analyzed.

• 한국해양공학회지
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• 제14권3호
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• pp.61-65
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• 2000

The estimation of soil stabilization is of great importance concerning the construction of structures on weak soil. A typical model of soil stabilization is considered as replacement, which is based on ground at failure due to direct loading on weak soil. The calculation of the line of predicting settlement was carried out using RPL and DIKE programs. The DIKE program is showing a tendency to excel totally about this embankment of the seadike. Hereafter, This program will be contributed widely to the construction of offshore structures on weak soil.

• Journal of the Korean Data and Information Science Society
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• 제14권4호
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• pp.889-901
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• 2003

In this paper, we consider the optimal replacement policies following the expiration of the combination warranty. The combination warranty can be divided into the renewing combination warranty and the non-renewing combination warranty. The criterion used to determine the optimal replacement period is the overall value function based on the expected cost and the expected downtime. Thus, we obtain the expected cost rate per unit time and the expected downtime per unit time for our model. And then the overall value function suggested by Jiagn and Ji(2002) is applied to obtain the optimal replacement period. The numerical examples are presented for illustrative purpose.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권2호
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• pp.77-86
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• 2013

Recently, an extended warranty of a system following the expiration of the basic warranty is becoming increasingly popular to the user. In this respect, we suggest a replacement model following the expiration of extended warranty with minimal repair warranty from the user's point of view in this paper. Under extended warranty, the failed system is minimally repaired by the manufacturer at no cost to the user during the original extended warranty period. As a criterion of the optimality, we utilize the expected cost rate per unit time during the life cycle from the user's perspective and suggest the optimal replacement period after extended warranty. Finally, a few numerical examples are given for illustrative purpose.

• 대한산업공학회지
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• 제39권4호
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• pp.233-238
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• 2013

This article concerns a profit model in a repair limit replacement problem with imperfect repair. If a system fails, we should decide whether we repair the failed system (repair option) or replace it by new one (replacement option with a lead time). We assume that repair times are random variables and can be estimated before repair with estimation error. If the estimated repair time is less than the specified limit (repair time limit), the failed unit is repaired but the unit after repair is different from the new one (imperfect repair). Otherwise, we order a new unit to replace the failed unit. The long run average profit (expected profit rate) is used as an optimization criterion and the optimal repair time limit maximizes the expected profit rate. Some special cases are derived.

• 대한약학회:학술대회논문집
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• 대한약학회 2003년도 Proceedings of the Convention of the Pharmaceutical Society of Korea Vol.1
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• pp.310.2-311
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• 2003

The effects of differences in the rate and composition of intravenous fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of torasemide were evaluated using rabbits as the animal model. Each rabbit received 2-h constant intravenous infusion of 1 mg/kg ∼ 1 of torasemide with 0％ replacement (treatment I, n = 6), 50％ replacement (treatment II, n = 9), and 100％ replacement with lactated Ringer's solution (treatment III, n = 8) as well as with 100％ replacement with 5％ dextrose in water(D-5-W, treatment IV, n=6). (omitted)

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.947-952
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• 2001

The prediction model is proposed to estimate the variation of compressive strength of fly ash concrete with aging. After analyzing the experimental result with the model, the regression results are presented according to fly ash replacement content and water/cement ratio. Based on the regression results, the influence of fly ash replacement content and water/cement ratio on apparent activation energy was investigated. According to the analysis, the model provides a good estimate of compressive strength development of fly ash concrete with aging. As the fly ash replacement content increases, the limiting relative compressive strength and initial apparent activation energy become greater. The concrete with water/cement ratio smaller than 0.40 shows that the limiting relative compressive strength and apparent activation energy are nearly constant according to water/cement ratio. But, the concrete with water/cement ratio greater than 0.40 has the increasing limiting relative compressive strength and apparent activation energy with increasing water/cement ratio.

• Journal of the Korean Data and Information Science Society
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• 제23권6호
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• pp.1195-1202
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• 2012

본 논문에서는 최소수리의 비용이 시스템의 수명시간에 의존하는 경우에 연장된 보증이 주어진 수리가 가능한 시스템에 대하여 사용자 측면에서의 총기대비용을 구하였다. 이를 위해서 연장된 보증을 정의하고 사용자 측면에서 연장된 보증이 종료된 이후의 교체모형을 가정하였다. 특히, 시스템의 교체모형에서 사용자가 연장된 보증을 선택하기 위한 기준을 제시하였으며, 시스템의 고장시간이 와이블 분포를 따를 때 수치적 예를 통하여 이를 설명하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.299-306
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• 2001

Crushed Stone Pile(CSP) is one of the ground improvement methods available to loose sand and clayey ground by forming compacted CSP in the weak soil layer. The effects of this method are enhancement of ground bearing capacity, reduction of settlement and prevention of lateral ground movement in cohesive layer, reduction of liquefaction potential in sandy ground. This study performs model tests in 1.0m${\times}$1.0m${\times}$1.0m and 1.5m${\times}$1.5m${\times}$l.2m model tank to observe bearing capacity of CSP treated ground. The area replacement ratio of CSP composite ground varies 20%, 30% and 40% with square grid pattern. After the composite ground was consolidated under pressure of 0.5kg/$\textrm{cm}^2$ and 1.0kg/$\textrm{cm}^2$, load tests were carried out. The results show that ultimate bearing capacity increases with area replacement ratio and the preconsolidation pressure of ground.