12 results on '"Xufeng Zhao"'
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2. Optimal Inspection Policies to Minimize Expected Cost Rates
- Author
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Satoshi Mizutani, Xufeng Zhao, and Toshio Nakagawa
- Subjects
Nuclear Energy and Engineering ,General Computer Science ,Energy Engineering and Power Technology ,Aerospace Engineering ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,Industrial and Manufacturing Engineering - Abstract
In this paper, we propose a computing algorithm to obtain optimal checking times which minimize the expected cost rate of sequential inspection models. This algorithm is applied to two modified inspection models with finite intervals such that the unit is checked at times [Formula: see text] ([Formula: see text]) for given [Formula: see text] and given [Formula: see text]. The modified algorithms are proposed and optimal checking times to minimize the expected cost rates are obtained. Numerical examples of each model are given to show how to use the algorithm. This method would be applied to other sequential inspection models by its suitable modifications.
- Published
- 2022
- Full Text
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3. Optimizations of Managerial Maintenance Policies
- Author
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Jiajia Cai, Xufeng Zhao, and Xiaoning Zhang
- Subjects
Nuclear Energy and Engineering ,General Computer Science ,Energy Engineering and Power Technology ,Aerospace Engineering ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,Industrial and Manufacturing Engineering - Abstract
This paper takes up managerial maintenance policies during different phases for mission executions. When a mission execution is divided into two phases and three phases respectively, replacement, minimal repair and keeping failure status become alternatives for managerial maintenance policies. Further, we give approximations of the above managerial maintenance policies to make the computations simple. In this paper, keeping failure status is considered as the last choice for the last phase of mission executions. We aim to minimize the expected maintenance costs for the total mission executions. All of the discussions are made analytically and their numerical examples are given.
- Published
- 2021
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4. Replacement Policies for an Independent Damage Process
- Author
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Xufeng Zhao, Toshio Nakagawa, and Satoshi Mizutani
- Subjects
021103 operations research ,General Computer Science ,Computer science ,Process (engineering) ,05 social sciences ,0211 other engineering and technologies ,Energy Engineering and Power Technology ,Aerospace Engineering ,02 engineering and technology ,Industrial and Manufacturing Engineering ,Preventive replacement ,Reliability engineering ,Reliability (semiconductor) ,Nuclear Energy and Engineering ,0502 economics and business ,Damages ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,050203 business & management - Abstract
This paper discusses preventive replacement policies for an independent damage process, in which successive shocks occur at random times, and the independent damages caused by shocks are random variables. It is assumed that a unit fails when the damage has exceeded a prespecified level [Formula: see text]. We consider three models: Model 1: the unit is replaced at the [Formula: see text]th shock for damage [Formula: see text], at damage [Formula: see text], or at time [Formula: see text], whichever occurs first. Model 2: the unit is replaced at the [Formula: see text]th shock for damage [Formula: see text], at damage [Formula: see text] or at shock [Formula: see text], whichever occurs first. Model 3: the unit is replaced at the [Formula: see text]th shock for damage [Formula: see text], at damage [Formula: see text], at shock [Formula: see text] or at time [Formula: see text], whichever occurs first. We obtain the expected cost rates for each model and discuss analytical optimal [Formula: see text] and [Formula: see text] to minimize their expected cost rates. Numerical examples are given when the damage has an exponential distribution and shocks occur at a gamma distribution.
- Published
- 2020
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5. Random Age Replacement Policies with Periodic Planning Times
- Author
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Xufeng Zhao, Toshio Nakagawa, and Satoshi Mizutani
- Subjects
021103 operations research ,General Computer Science ,Random replacement ,Computer science ,0211 other engineering and technologies ,Energy Engineering and Power Technology ,Aerospace Engineering ,02 engineering and technology ,01 natural sciences ,Industrial and Manufacturing Engineering ,010104 statistics & probability ,Nuclear Energy and Engineering ,Statistics ,0101 mathematics ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality - Abstract
The random age replacement policies discussed in literatures are helpful to complete the nonstopping works with random working cycles, however, maintenance policies are more easily performed at periodic times in real applications. For such a viewpoint, this paper proposes that age replacement policies are planned at periodic times while considering the random working cycles. Using the modeling approaches of replacement first and last policies, we discuss two models such that the unit is replaced at periodic times [Formula: see text] and working cycles [Formula: see text], whichever occurs first and whichever occurs last. The expected cost rate models are obtained and their optimal solutions for [Formula: see text] and [Formula: see text] are discussed. The comparisons between the policies of [Formula: see text] and [Formula: see text], and replacement first and last are made from the point of cost. Numerical examples are illustrated when the failure time has a Weibull distribution.
- Published
- 2019
- Full Text
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6. Optimum Backup Policies with Update Failure at Random Times
- Author
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Cunhua Qian, Xufeng Zhao, and Syouji Nakamura
- Subjects
General Computer Science ,business.industry ,Computer science ,Energy Engineering and Power Technology ,Aerospace Engineering ,Data security ,Industrial and Manufacturing Engineering ,Data recovery ,Reliability engineering ,Set (abstract data type) ,Nuclear Energy and Engineering ,Order (business) ,Backup ,Data_FILES ,Electrical and Electronic Engineering ,Differential (infinitesimal) ,Safety, Risk, Reliability and Quality ,business - Abstract
In order to ensure the data security, plans of incremental and differential backups are usually set up to save the costs which suffer from full backups. In this paper, we suppose that failures occur at data updating times and backups are implemented only at the end of data updates, and full backups are done at time [Formula: see text], over time [Formula: see text] and update [Formula: see text] to balance the costs of data backup and failure recovery. Using the theory of renewal process, we obtain the expected costs of backup and recovery and the expected cost rates for full backups. Optimum solutions of [Formula: see text] and [Formula: see text] to minimize the expected cost rates are obtained, and their comparisons are discussed from the optimizations of the integrated models in analytical ways.
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- 2019
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7. OPTIMAL AGE REPLACEMENT AND INSPECTION POLICIES WITH RANDOM FAILURE AND REPLACEMENT TIMES
- Author
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Won Young Yun, Xufeng Zhao, and Toshio Nakagawa
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Engineering ,General Computer Science ,Random replacement ,business.industry ,Energy Engineering and Power Technology ,Aerospace Engineering ,Economic shortage ,Industrial and Manufacturing Engineering ,Preventive replacement ,Exponential function ,Reliability engineering ,Nuclear Energy and Engineering ,Electrical and Electronic Engineering ,Finite time ,Safety, Risk, Reliability and Quality ,business - Abstract
It is well-known in the standard age replacement policy that a finite preventive replacement time does not exist when the failure time is exponential and the optimal preventive replacement time is nonrandom. It is shown that when the failure time is exponential, a finite time exists by introducing the shortage and excess costs. In addition, the random age replacement is proposed and similar discussions are made. Furthermore, the periodic and random inspection policies are taken up, and their optimal policies are shown to correspond theoretically to those of the age replacement ones. It is shown finally that when the random inspection cost is the half of the periodic one, two expected costs are almost the same.
- Published
- 2011
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8. Age Replacement Models with Constant and Random Replacement Times
- Author
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Cunhua Qian, Xufeng Zhao, and Toshio Nakagawa
- Subjects
021103 operations research ,General Computer Science ,Random replacement ,0211 other engineering and technologies ,Energy Engineering and Power Technology ,Aerospace Engineering ,02 engineering and technology ,01 natural sciences ,Industrial and Manufacturing Engineering ,Preventive replacement ,010104 statistics & probability ,Nuclear Energy and Engineering ,Statistics ,0101 mathematics ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,Constant (mathematics) ,Mathematics - Abstract
Preventive replacement policy conducted at a routine time [Formula: see text] has been surveyed extensively in literatures. Another two random replacement times [Formula: see text] and [Formula: see text] for time [Formula: see text] are jointly considered in this paper. We formulate the models of replacement first, replacement last and replacement middle, which are based on the respective assumptions of whichever occurs first, whichever occurs last and whichever occurs middle. Next, we modify replacement first and replacement last by using whichever occurs first and last jointly. Furthermore, we give the model of replacement overtime when the assumptions of whichever occurs first, whichever occurs last and replacing the unit over time [Formula: see text] are simultaneously considered. Comparisons among these replacement models are made to find which policy is more economical than the other.
- Published
- 2018
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9. Age Replacement Policies with Shortage and Excess Costs
- Author
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Xufeng Zhao, Toshio Nakagawa, and Mingchih Chen
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0209 industrial biotechnology ,021103 operations research ,General Computer Science ,Random replacement ,0211 other engineering and technologies ,Energy Engineering and Power Technology ,Aerospace Engineering ,Economic shortage ,02 engineering and technology ,Working time ,Industrial and Manufacturing Engineering ,020901 industrial engineering & automation ,Nuclear Energy and Engineering ,Operations management ,Business ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality - Abstract
It has been proposed in recent literatures that if replacement time is planned too early prior to failure time, a waste of operation cost, i.e., excess costs, would incur because the system might run for an additional period of time to complete critical operations; and if the replacement time is too late after failure, a great failure cost, i.e., shortage cost, is incurred due to the delay in time of the carelessly scheduled replacement. The above notion of shortage and excess costs are taken into consideration for the replacement first, replacement last and replacement overtime models in this paper. We obtain the expected cost rates and their optimum replacement times. Comparisons among these optimum times are made analytically and numerically.
- Published
- 2018
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10. Replacement Policies for Periodic Damage Models
- Author
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Khalifa N. Al-Khalifa, Xufeng Zhao, and Toshio Nakagawa
- Subjects
0209 industrial biotechnology ,Engineering ,over-damage replacement ,General Computer Science ,0211 other engineering and technologies ,Energy Engineering and Power Technology ,Aerospace Engineering ,Cumulative process ,02 engineering and technology ,Measure (mathematics) ,Industrial and Manufacturing Engineering ,020901 industrial engineering & automation ,replacement last ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,Event (probability theory) ,021103 operations research ,Expected cost ,business.industry ,Structural engineering ,Reliability engineering ,periodic damage ,Nuclear Energy and Engineering ,Cumulative damage ,business ,replacement first - Abstract
A new periodic damage model is proposed in this paper, where the damage produced by shocks is only measured at periodic times, without considering the stochastic shocks and the cumulative process of damage in discrete times. We model five replacement policies for the periodic damage models using three approaches of whichever triggering event occurs first, whichever triggering event occurs last, and replacing over a planned measure, which are named as replacement first, replacement last, over-damage replacement, over-damage replacement first, and over-damage replacement last, respectively. In analytical ways, we obtain their optimum replacement policies to minimize the expected cost rates and compare them to find which model is more economical. Finally, numerical examples are given to illustrate the validity of the presented models. This paper was made possible by PDRA Grant # PDRA1-0116-14107 from the Qatar National Research Fund (a member of The Qatar Foundation), and NPRP 4-631-2-233 Scopus
- Published
- 2017
- Full Text
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11. Constant and Random Full Backup Models with Incremental and Differential Backup Schemes
- Author
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Xufeng Zhao, Syouji Nakamura, and Toshio Nakagawa
- Subjects
Mathematical optimization ,General Computer Science ,Computer science ,Real-time computing ,Energy Engineering and Power Technology ,Aerospace Engineering ,010103 numerical & computational mathematics ,02 engineering and technology ,01 natural sciences ,Industrial and Manufacturing Engineering ,database failure ,Data recovery ,Set (abstract data type) ,Backup ,Data_FILES ,0202 electrical engineering, electronic engineering, information engineering ,0101 mathematics ,Electrical and Electronic Engineering ,Differential (infinitesimal) ,incremental backup ,Safety, Risk, Reliability and Quality ,business.industry ,020207 software engineering ,Incremental backup ,data update ,Exponential function ,Decision variables ,Nuclear Energy and Engineering ,Random backup ,business ,Constant (mathematics) ,data recovery - Abstract
It has been commonly known in a Database Management System that constant plans of incremental/differential backup schemes are set up and their full backups should be done to balance the costs of data backup and failure recovery. In this paper, we consider a database system that is running for 24/7 and has several random busy states of updates, and we suppose that incremental/differential backups are implemented after each update and full backups are triggered at constant time [Formula: see text] and random updates [Formula: see text]. That is, models with decision variables of [Formula: see text] and [Formula: see text] for full backups with random incremental/differential backups are considered. We obtain the expected costs of data backup and failure recovery and the expected cost rates for full backups. Optimum solutions to minimize the expected cost rates are discussed in analytical ways. Furthermore, full backups that are made at time [Formula: see text] and updates [Formula: see text] are considered as constant and random modes respectively and compared analytically. For the discussions, numerical examples in exponential cases are given.
- Published
- 2017
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12. AGE AND PERIODIC REPLACEMENT MODELS WITH OVERTIME POLICIES
- Author
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Xufeng Zhao, Syouji Nakamura, and Cunhua Qian
- Subjects
Engineering ,General Computer Science ,Operations research ,Expected cost ,Random replacement ,business.industry ,Energy Engineering and Power Technology ,Aerospace Engineering ,Overtime ,Working time ,Industrial and Manufacturing Engineering ,Nuclear Energy and Engineering ,Electrical and Electronic Engineering ,Safety, Risk, Reliability and Quality ,business - Abstract
This paper proposes two modified replacement policies which combine random replacement with standard age and periodic policies, where units undergo replacement at the first completion of some random working time over a planned time T, which are called replacement overtime. The expected cost rates of age and periodic replacement overtime polices are obtained, and optimal policies which minimize them are discussed analytically. Comparisons between such two overtime policies and standard age and periodic replacements are made in detail. When two costs for replacement overtime and standard age or periodic policies are the same, it is shown as estimated previously that the standard replacements are better than their overtime policies. Furthermore, two modified replacement overtime costs are discussed and computed numerically when such new policies would be better than the standard age and periodic replacements.
- Published
- 2014
- Full Text
- View/download PDF
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