• Title/Summary/Keyword: Failure-time

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An Optimal Block Replacement Policy Using Items with Different Reliability

  • Lie, Chang-Hoon;Bae, Moon-Sik;Chun, Young-Ho
    • Journal of the military operations research society of Korea
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    • v.10 no.2
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    • pp.61-73
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    • 1984
  • A block replacement policy using items with different reliability is discussed. We divide system unit failure modes into two modes and use less reliable unit when operating unit fails near the planned preventive replacement time. In this policy, item A has two failure modes. Mode-1 failure is removed by minimal repair, mode-2 failure by replacement. If mode-2 failure of item A happens in (0, $T-{\delta}$), failure item A is replaced by new item A. If mode-2 failure of item A happens in ($T-{\delta}$, T), failure item A is replaced by new item B. Item B should be cheaper and less durable than item A. Under this policy, we determine the preventive replacement interval $T^{*}$ and the interval ${\delta}^{*}$ of item B replacement which minimize the cost rate per unit time.

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Block 대체정책에 관한 연구

  • Bae, Mun-Sik
    • ETRI Journal
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    • v.6 no.3
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    • pp.17-20
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    • 1984
  • A block replacement policy using items with different reliability is discussed. We devide system unit failure modes into two modes and use less reliable unit when operating unit fails near the planned preventive replacement time. In this policy, item A has two failure modes. Mode-1 failure is removed by minimal repair, mode-2 failure by replacement. If mode-2 failure of item A happens in (0,T- $\delta$). failure item A is replaced by new item A. If mode-2 failure of item A happens in(T-$\delta$,T), failure item A is replaced by new item B. Item B should be cheaper and less durable than item A. Under this policy, we determine the preventive replacement interval T and the interval $\delta$ of item B replacement which minimize the cost rate per unit time.

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Lifetime Prediction of Geogrids for Reinforcement of Embankments and Slopes through Time-Temperature Superposition

  • Koo, Hyun-Jin;Kim, You-Kyum;Kim, Dong-Whan
    • Corrosion Science and Technology
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    • v.4 no.4
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    • pp.147-154
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    • 2005
  • The creep resistance of geogrids is one of the most significant long-term safety characteristics used as the reinforcement in slopes and embankments. The failure of geogrids is defined as creep strain greater than 10%. In this study, the accelerated creep tests were applied to polyester geogrids at various loading levels of 30, 50% of the yield strengths and temperatures using newly designed test equipment. Also, the new test equipment permitted the creep testing at or above glass transition temperature($T_g$) of 75, 80, $85^{\circ}C$. The time-dependent creep behaviors were observed at various temperatures and loading levels. And then the creep curves were shifted and superposed in the time axis by applying time-temperature supposition principles. The shifting factors(AFs) were obtained using WLF equation. In predicting the lifetimes of geogrids, the underlying distribution for failure times were determined based on identification of the failure mechanism. The results confirmed that the failure distribution of geogrids followed Weibull distribution with increasing failure rate and the lifetimes of geogrids were close to 100 years which was required service life in the field with 1.75 of reduction factor of safety. Using the newly designed equipment, the creep test of geogrids was found to be highly accelerated. Furthermore, the time-temperature superposition with the newly designed test equipment was shown to be effective in predicting the lifetimes of geogrids with shorter test times and can be applied to the other geosynthetics.

Methodologies of Duty Cycle Application in Weapon System Reliability Prediction (무기체계 신뢰도 예측시 임무주기 적용 방안에 대한 연구)

  • Yun, Hui-Sung;Jeong, Da-Un;Lee, Eun-Hak;Kang, Tae-Won;Lee, Seung-Hun;Hur, Man-Og
    • Journal of Applied Reliability
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    • v.11 no.4
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    • pp.433-445
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    • 2011
  • Duty cycle is determined as the ratio of operating time to total time. Duty cycle in reliability prediction is one of the significant factors to be considered. In duty cycle application, non-operating time failure rate has been easily ignored even though the failure rate in non-operating period has not been proved to be small enough. Ignorance of non-operating time failure rate can result in over-estimated system reliability calculation. Furthermore, utilization of duty cycle in reliability prediction has not been evaluated in its effectiveness. In order to address these problems, two reliability models, such as MIL-HDBK-217F and RIAC-HDBK-217Plus, were used to analyze non-operating time failure rate. This research has proved that applying duty cycle in 217F model is not reasonable by the quantitative comparison and analysis.

Prediction of MTBF Using the Modulated Power Law Process

  • Na, Myung-Hwan;Son, Young-Sook;Yoon, Sang-Hoo;Kim, Moon-Ju
    • Journal of the Korean Data and Information Science Society
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    • v.18 no.2
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    • pp.535-541
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    • 2007
  • The Non-homogeneous Poisson process is probably the most popular model since it can model systems that are deteriorating or improving. The renewal process is a model that is often used to describe the random occurrence of events in time. But both these models are based on too restrictive assumptions on the effect of the repair action. The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose maximum likelihood estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model.

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Reliability estimation for shared load model with guarantee time under censoring scheme (중도절단계획 하에서 보증시간을 가지는 부하분배모형의 신뢰도추정)

  • Cha, Young-Joon
    • Journal of the Korean Data and Information Science Society
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    • v.20 no.3
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    • pp.467-474
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    • 2009
  • There are many situations arising in reliability engineering and biomedical science where failure of a subsystem increases the failure rate of other subsystem under shared load models. In this paper, the maximum likelihood estimates and the modified maximum likelihood estimates of mean time to failure and reliability function for shared load model with guarantee time are obtained by using censored system life data. Some illustrative examples are included.

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Preventive Policy With Minor Failure Under Age and Periodic Replacement (경미한 고장을 수반하는 시스템에 대한 노화 및 예방적 교체 정책)

  • Lee, Jinpyo
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.45 no.3
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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.

Development of a New Software to Analyze Displacement and Predict Failure Time of the Rock Slope (암반사면 변위자료 분석 및 파괴시간 예측 소프트웨어 개발)

  • Noh, Young-Hwan;Um, Jeong-Gi
    • Tunnel and Underground Space
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    • v.25 no.1
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    • pp.76-85
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    • 2015
  • We have developed a software to predict failure time of the rock slope based on analysis of the data from real time displacement measurements with respect to time. The software consists of four modules that play roles in analytical methods such as inverse velocity method, log time-log velocity method, log velocity-log acceleration method and nonlinear least square method to estimate failure time. VisualBasic.NET on the MS Visual Studio platform was utilized as a development tool to efficiently implement the modules and the graphical user interface of the software. Displacement data obtained from laboratory physical model studies of plane sliding were used to explore the applicability of the software, and to evaluate the possibility of predicting potential slope failure. It seems possible to estimate failure time using developed software for sliding plane having exponential type of deformability.

An Application of Dirichlet Mixture Model for Failure Time Density Estimation to Components of Naval Combat System (디리슈레 혼합모형을 이용한 함정 전투체계 부품의 고장시간 분포 추정)

  • Lee, Jinwhan;Kim, Jung Hun;Jung, BongJoo;Kim, Kyeongtaek
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.42 no.4
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    • pp.194-202
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    • 2019
  • Reliability analysis of the components frequently starts with the data that manufacturer provides. If enough failure data are collected from the field operations, the reliability should be recomputed and updated on the basis of the field failure data. However, when the failure time record for a component contains only a few observations, all statistical methodologies are limited. In this case, where the failure records for multiple number of identical components are available, a valid alternative is combining all the data from each component into one data set with enough sample size and utilizing the useful information in the censored data. The ROK Navy has been operating multiple Patrol Killer Guided missiles (PKGs) for several years. The Korea Multi-Function Control Console (KMFCC) is one of key components in PKG combat system. The maintenance record for the KMFCC contains less than ten failure observations and a censored datum. This paper proposes a Bayesian approach with a Dirichlet mixture model to estimate failure time density for KMFCC. Trends test for each component record indicated that null hypothesis, that failure occurrence is renewal process, is not rejected. Since the KMFCCs have been functioning under different operating environment, the failure time distribution may be a composition of a number of unknown distributions, i.e. a mixture distribution, rather than a single distribution. The Dirichlet mixture model was coded as probabilistic programming in Python using PyMC3. Then Markov Chain Monte Carlo (MCMC) sampling technique employed in PyMC3 probabilistically estimated the parameters' posterior distribution through the Dirichlet mixture model. The simulation results revealed that the mixture models provide superior fits to the combined data set over single models.

Fault Tolerant Control with Variable Time Weight (가변시간비중을 갖는 내고장성 제어)

  • Hee Gyoo Lee;Zeungnam Bien
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.29B no.4
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    • pp.22-30
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    • 1992
  • A redundant control scheme which can maintain its tracking capability in the case of a controller failure is proposed for the industrial applications which need high reliability with fault-tolerance. It consists of two identical controllers and a switching mechanism which includes failure detection and reconfiguration algorithm. The new detection method against controller failure using fuzzy logic enables the detection of controller failures without failure assumptions through the instability of the failed controller. The failed controller is smoothly removed from the control loop by reducing time weight of the failed controller.

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