• Journal of Navigation and Port Research
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• v.32 no.3
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• pp.167-172
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• 2008

The aim of this paper is to determine the replacement time of containerships in economical viewpoint. Especially, there was a lot of vagueness to the cost data for calculation of an economical life in a containership. For this, a fuzzy number used to express the vague nature about a cost data. This paper developed the fuzzy cost model using fuzzy numbers, and to analyze more practically than the existing cost model. And the proposal model used to decide the economical life about various kinds of containerships.

• Journal of Korean Society on Water Environment
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• v.23 no.3
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• pp.356-366
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• 2007

In this paper a methodology is developed to prioritize replacement of water distribution pipes according to the economical efficiency of replacement and assess the long-term effects of water main replacement policies on water distribution systems. The methodology is implemented with MATLAB to develop a computer algorithm which is used to apply the methodology to a case study water distribution system. A pipe break prediction model is used to estimate future costs of pipe repair and replacement, and the economically optimal replacement time of a pipe is estimated by obtaining the time at which the present worth of the total costs of repair and replacement is minimum. The equation for estimating the present worth of the total cost is modified to reflect the fact that a pipe can be replaced in between of failure events. The results of the analyses show that about 9.5% of the pipes in the case study system is required to be replaced within the planning horizon. Analyses of the yearly pipe replacement requirements for the case study system are provided along with the compositions of the replacement. The effects of water main replacement policies, for which yearly replacement length scenario and yearly replacement budget scenario are used, during a planning horizon are simulated in terms of the predicted number of pipe failures and the saved repair costs.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.279-285
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• 2009

In this study, applied to the industrial water service, it is verified feasibility of break-even analysis method which has not been introduced in Korea. The On-san water pipeline of 7.1km among the Ul-san industrial water service is selected and the optimal replacement time calculated by break-even analysis method is year 2033 to 2044 which will be 53 to 67 years since the pipes were buried. If indirect cost such as the value of lost water and traffic disruption, service interruption, etc. is calculated as 30 and 100% of the direct cost, the financially optimum replacement time is advanced 3 to 9 years. These ways present rational criteria to establish long-term plan for budget and to execute the limited budget efficiently.

• Journal of Korea Water Resources Association
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• v.42 no.6
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• pp.457-464
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• 2009

This paper proposes methodologies for analyzing the accuracy of the proportional hazards model in predicting consecutive break times of water mains and estimating the time interval for economical water main replacement. By using the survival functions that are based on the proportional hazards models a criterion for the prediction of the consecutive pipe breaks is determined so that the prediction errors are minimized. The criterion to predict pipe break times are determined as the survival probability of 0.70 and only the models for the third through the seventh break are analyzed to be reliable for predicting break times for the case study pipes. Subsequently, the criterion and the estimated lower and upper bound survival functions of consecutive breaks are used in predicting the lower and upper bounds of the 95% confidence interval of future break times of an example water main. Two General Pipe Break Prediction Models(GPBMs) are estimated for an example pipe using the two series of recorded and predicted lower and upper bound break times. The threshold break rate is coupled with the two GPBMs and solved for time to obtain the economical replacement time interval.

• Journal of Korean Society for Quality Management
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• v.20 no.2
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• pp.33-43
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• 1992

Items are assumed to fail by degradation. An appropriate stochastic model of such item is a cumulative process in which an item can fail only when the total amount of wear exceeds a prespecified failure level. This paper presents replacement policy in which an item is replaced at a certain level of wear before failure or at failure, whichever occurs first. Yet, when measuring the item wear level is very expensive, destructive or time-consuming, it may be economical to use substitutive characteristics that are correlated with the item wear level and relatively inexpensive to measure. The item's wear level could usually be estimated by monitoring such substitutive characteristics only except for a breakdown, which may be observed immediately at its occurrence. The purpose of this paper is to find an optimal periodic replacement policy based on such substitutive characteristics that balance the cost of replacement with the cost of failure and result in a minimum total long-run average cost per unit time. The optimal level of substitutive characteristics to replace the item is obtained. Numerical example illustrate how the model can be used to determine the optimal replacement policy.

• Journal of Applied Reliability
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• v.5 no.3
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• pp.373-379
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• 2005

In many cases, it is more practical and economical to repair a system than to replace the whole system or to perform a complete overhaul when the system fails. Two basic replacement policies were proposed by Barlow and Hunter(1960) and Morimura (1970), in which the minimal repair times are identically distributed. But, as Lam(1988) pointed out, in many cases of deteriorating system, in view of ageing and cumulative wear, the repair time will tend to be longer and longer. In this note, the two basic replacement policies are considered for a repairable system with linearly increasing repair times. Optimal policies, which maximize the steady state availability of the system, are obtained for the Weibull failure rate case.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.209-210
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• 2009

In constuction work, the early compressive strength in reference to the demolding time of side forms is significant on reducing the construction time and improving the economical efficiency. Therefore, this study is investigated the effect of the kind and replacement ratio of mineral admixture on the development of early strength.

• Journal of Korean Society for Quality Management
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• v.28 no.3
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• pp.53-58
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• 2000

In many cases, it is more practical and economical to repair a system than to replace the whole system or to perform a complete overhaul when it fails. The age replacement policy with minimal repair at failure is considered. The system is replaced every time its age reaches at $T_0$. For each intervening failure only minimal repair is done. The minimal repair times in a renewal period are increasing in the sense that the minimal repair times constitute a strictly increasing geometric process. The long-run expected cost rate Is obtained and the properties of the existence and the uniqueness of the optimal policy minimizing the long-run expected cost rate are derived.

• International Journal of Concrete Structures and Materials
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• v.9 no.2
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• pp.241-254
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• 2015

A lot of reinforced concrete (RC) structures in Syria went out of service after a few years of construction. This was mainly due to reinforcement corrosion or chemical attack on concrete. The use of blended cements is growing rapidly in the construction industry due to economical, ecological and technical benefits. Syria is relatively rich in scoria. In the study, mortar/concrete specimens were produced with seven types of cement: one plain Portland cement (control) and six blended cements with replacement levels ranging from 10 to 35 %. Rapid chloride penetration test was carried in accordance with ASTM C 1202 after two curing times of 28 and 90 days. The effect on the resistance of concrete against damage caused by corrosion of the embedded steel has been investigated using an accelerated corrosion test by impressing a constant anodic potential. The variation of current with time and time to failure of RC specimens were determined at 28 and 90 days curing. In addition, effects of aggressive acidic environments on mortars were investigated through 100 days of exposure to 5 % $H_2SO_4$, 10 % HCl, 5 % $HNO_3$ and 10 % $CH_3COOH$ solutions. Evaluation of sulfate resistance of mortars was also performed by immersing in 5 % $Na_2SO_4$ solution for 52 weeks. Test results reveal that the resistance to chloride penetration of concrete improves substantially with the increase of replacement level, and the concretes containing scoria based-blended cements, especially CEM II/B-P, exhibited corrosion initiation periods several times longer than the control mix. Further, an increase in scoria addition improves the acid resistance of mortar, especially in the early days of exposure, whereas after a long period of continuous exposure all specimens show the same behavior against the acid attack. According to results of sulfate resistance, CEM II/B-P can be used instead of SRPC in sulfate-bearing environments.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.3
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• pp.249-254
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• 2004

The radiation dosage of nuclear fuel handling machine of PHWR type NPP during normal operation is measured using semiconductor detectors. In order to predict and mitigate the damage of main components in fuel handling machine, caused by high irradiation, the radiation dosage exerted to the components by neutron and gamma ray is measured independently during one time of the fuel exchange, which is used far estimating the radiation dosage for one year. This result can guarantee the safety and economical efficiency for determining the replacement time of the high cost main components in fuel handling machine.