| 1. |
- Ahmadi, Alireza, et al.
(författare)
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Cost based risk analysis to identify inspection and restoration intervals of hidden failures subject to aging
- 2011
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; 60:1, s. 197-209
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Tidskriftsartikel (refereegranskat)abstract
- The analytical model presented in this paper aims to study possible maintenance strategies considering risk constrains, to preserve or assure availability of hidden functions of a repairable unit in aircraft systems considering ageing effect. The paper discusses two known strategies for hidden failure management aviation and other high risk industries, namely Failure Finding Inspection (FFI), and a combination of a series of FFI and restoration after a specific number of FFI cycles ( i.e., FFI-Rs strategy). Based on discussions, the paper introduces a new approach named Dynamic Failure Finding Inspection strategy (DFFI) to assure the acceptable level of risk and also the unit's hidden function availability continuously . The paper presents analytical methods to estimate optimal FFI, and optimal thresholds for restoration of degradation (refreshing risk level) within FFI-Rs strategy. It also discusses criteria used to select appropriate thresholds to change the FFI intervals within DFFI strategy, i.e. reducing inspection intervals after specific thresholds, to reduce the risk. The method is based on the mean proportion of time i.e. (Mean Functional Dead Time, MFDT) that the unit is not functioning during the inspection intervals and the average unavailability behavior within the restoration/discard period. The proposed method considers inspection, repair, and restoration times, and takes in to account costs associated with inspection, repair, restoration, potential losses due to non-availability of aircraft due to maintenance downtime or accident often caused multiple failures.
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| 2. |
- Bergman, Bo, et al.
(författare)
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A graphical method applicable to age-replacement problems
- 1982
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; R-31:5, s. 478-481
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Tidskriftsartikel (refereegranskat)abstract
- The Total Time on Test (TTT) concept has proven to be a very useful tool in several reliability contexts. The objective of this note is to illustrate how a generalization of the TTT-concept, the TTT-transform, defined as a certain function of the survivor function, can be used when analyzing different types of age-replacement problems. (14 refs.)
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| 3. |
- Bures, Miroslav, et al.
(författare)
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Tapir : Automation Support of Exploratory Testing Using Model Reconstruction of the System Under Test
- 2018
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Ingår i: IEEE Transactions on Reliability. - : IEEE. - 0018-9529 .- 1558-1721. ; 67:2, s. 557-580
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Tidskriftsartikel (refereegranskat)abstract
- For a considerable number of software projects, the creation of effective test cases is hindered by design documentation that is either lacking, incomplete, or obsolete. The exploratory testing approach can serve as a sound method in such situations. However, the efficiency of this testing approach strongly depends on the method, the documentation of explored parts of a system, the organization and distribution of work among individual testers on a team, and the minimization of potential (very probable) duplicities in performed tests. In this paper, we present a framework for replacing and automating a portion of these tasks. A screen-flow-based model of the tested system is incrementally reconstructed during the exploratory testing process by tracking testers' activities. With additional metadata, the model serves for an automated navigation process for a tester. Compared with the exploratory testing approach, which is manually performed in two case studies, the proposed framework allows the testers to explore a greater extent of the tested system and enables greater detection of the defects present in the system. The results show that the time efficiency of the testing process improved with the framework support. This efficiency can be increased by team-based navigational strategies that are implemented within the proposed framework, which is documented by another case study presented in this paper.
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| 4. |
- Franke, Ulrik, et al.
(författare)
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The Distribution of Time to Recovery of Enterprise IT Services
- 2014
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; 63:4, s. 858-867
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Tidskriftsartikel (refereegranskat)abstract
- The context of this article is the availability of enterprise IT services, a key concern for many enterprises. While there is a plethora of literature concerned with service availability, there is no previous systematic empirical study on IT service time to recovery following outages. The existing literature typically assumes a distribution, or builds on analogies to related areas such as software engineering. Therefore, our objective is to find the statistical distribution of IT service time to recovery. Method-wise, this investigation is based on logs of more than 1 800 incidents in a large Nordic bank, corresponding to more than 11 000 hours of recorded downtime. Five possible distributions of time to recovery from the literature were investigated using the Akaike Information Criterion to find the distribution offering the best fit. The results show that the log-normal distribution outperformed the others for all tested service channels (collections of IT services). It is concluded that the log-normal distribution offers the best fit of IT service time to recovery. Using this distribution in simulation and decision-support tools offers the prospect of better predictions of downtime and downtime costs to the practitioner community.
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| 5. |
- Fuqing, Yuan, et al.
(författare)
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A general imperfect repair model considering time-dependent repair effectiveness
- 2012
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; 61:1, s. 95-100
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Tidskriftsartikel (refereegranskat)abstract
- Kijima I and Kijima II models are two important imperfect repair models in literature. These two models use one constant parameter to represent the degree of repair, which is called Repair Effectiveness (RE) in this paper. We developed a more general imperfect repair model by extending the constant RE to a time-dependent function based on the virtual age process, where the Kijima models are special cases of the new model. A simulation method is developed to estimate the cumulative number of failures for the new model, and a Bayesian inference method is proposed to select the best imperfect repair model. Finally, to demonstrate the new model, a numerical example is provided. From this example, the new model shows a more accurate mean and a narrower confidence interval than that of the Non-Homogeneous Poisson Processes, and Kijima I and Kijima II models.
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| 6. |
- Fuqing, Yuan, et al.
(författare)
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Kernelized proportional intensity model for repairable systems considering piecewise operating conditions
- 2012
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; 61:3, s. 618-624
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Tidskriftsartikel (refereegranskat)abstract
- The proportional intensity model (PIM) has been used to model the intensity function of repairable systems taking non-time factors, such as operating conditions, and repair history, into consideration. This paper develops a kernelized PIM (KPIM) by combining the PIM and the kernel method to consider a scenario where a repairable system experiences piecewise operating conditions. The kernel method is used to approximate the PIM covariate function nonlinearly. An approach based on the regularized likelihood function is proposed to obtain the optimal parameters for the KPIM. A numerical example is provided to demonstrate the KPIM model, and the parameter estimation approach
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| 7. |
- Klefsjö, Bengt, et al.
(författare)
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Goodness-of-fit tests for the power-law process based on the TTT-plot
- 1992
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Ingår i: IEEE Transactions on Reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9529 .- 1558-1721. ; 41:4, s. 593-598
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Tidskriftsartikel (refereegranskat)abstract
- The total-time-on-test plot (TTT-plot) and its theoretical counterpart, the scaled TTT-transform, are reviewed. It is shown how the TTT-plot can be used as a basis for goodness-of-fit tests for the power-law process when data are available from a repairable system. Both a subjective graphical procedure and an analytical test procedure based on the cumulative TTT-statistic are studied (19 refs.)
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| 8. |
- Klefsjö, Bengt
(författare)
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On closure under formation of parallell systems
- 1984
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; R-33:5, s. 423-
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that a parallel system of s-independent identical components has the same aging property (for example, increasing failure rate or increasing average failure rate) as the components (6 refs.)
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| 9. |
- Kumar, Dhananjay, et al.
(författare)
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Proportional hazards modeling of time-dependent covariates using linear regression : a case study
- 1996
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Ingår i: IEEE Transactions on Reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9529 .- 1558-1721. ; 45:3, s. 386-392
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Tidskriftsartikel (refereegranskat)abstract
- In the proportional hazards model, the effect of a covariate is assumed to be time-invariant. In this paper a graphical method based on a linear regression model (LRM) is used to test whether this assumption is realistic. The variation in the effect of a covariate is plotted against time. The slope of this plot indicates the nature of the influence of a covariate over time. A covariate is time-dependent if a drastic change in the slope of the plot is found and the time-point, at which this drastic change occurs provides guideline in redefining a time-dependent covariate into two or more time-independent covariates. This method is applied to failure data of cables used for supplying power to electric mine loaders. The results obtained by applying only the proportional hazards model were misleading as the graphical method based on the LRM showed that one covariate was highly time-dependent. This graphical method should be used to supplement the proportional hazards model, not as a separate method. This avoids misinterpretation of the influence of a time-dependent covariate in the proportional hazards model. The proportional hazards model should be used to identify the most important covariates, while the LRM should be used as an explanatory tool to check the consistency of the influence of the covariates. The LRM involves matrix computations which can be quite time consuming for large data-sets. Also, tests for the statistically significant effect of a covariate are not yet well established in the model
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| 10. |
- Lin, Jing
(författare)
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A Two-stage Failure Model for Bayesian Change Point Analysis
- 2008
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Ingår i: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; 57:2, s. 388-393
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new approach for detecting certain change-points, which may disturb the evaluation of reliability models with covariates, via a two-stage failure model, and stochastic time-lagged regression functions. The proposed model is developed with the Bayesian survival analysis method, and thus the problems for censored (or truncated) data in reliability tests can be resolved. In addition, a Markov chain Monte Carlo method based on Gibbs sampling is used to dynamically simulate the Markov chain of the parameters’ posterior distribution. Finally, a numeric example is discussed to demonstrate the proposed model.
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