A sequential condition-based repair/replacement policy with non-periodic inspections for a system subject to continuous wear

This paper studies the availability and optimal maintenance policies for systems subject to competing failure modes under continuous and periodic inspections. The repair time distribution and maintenance cost are both dependent on the failure modes. We investigate the instantaneous availability and the steady state availability of the system maintained through several imperfect repairs before a replacement is allowed. Analytical expressions for system availability under continuous and periodic inspections are derived respectively. The availability models are then utilized to obtain the optimal inspection and imperfect maintenance policy that minimizes the average long-run cost rate. A numerical example for Remote Power Feeding System is presented to demonstrate the application of the developed approach.

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Reliability modeling for multi-state systems with a protective device considering multiple triggering mechanism

Proceedings of the Institution of Mechanical Engineers Part O Journal of Risk and Reliability ◽

10.1177/1748006x211013325 ◽

2021 ◽

pp. 1748006X2110133

Author(s):

Xian Zhao ◽

Rong Li ◽

Yu Fan ◽

Qingan Qiu

Keyword(s):

Failure Modes ◽

Operating Time ◽

Replacement Policy ◽

Economic Losses ◽

Residual Lifetime ◽

Cumulative Number ◽

Protective Device ◽

Triggering Mechanism ◽

Safety Critical ◽

Markov Chain Imbedding

Failures of safety-critical systems may result in irretrievable economic losses and significant safety hazards, thus enhancing the reliability of safety-critical system is crucial. As applied widely in engineering fields, protective devices are commonly equipped for the systems operating in shock environment to reduce external damage, which has not been taken into consideration in existing literatures. This paper investigates the reliability of multi-state systems with competing failure patterns supported by a protective device. According to the system failure modes, state-based and shock number-based triggering mechanism of the protective device are developed. That is, the protective device is triggered once the system state or cumulative number of shocks exceeds corresponding critical thresholds respectively. After being triggered, the protective device can reduce the probability of damaging shocks for the system. The protective device fails when the number of consecutive valid shocks reaches a threshold. Based on the constructed model, a finite Markov chain imbedding approach is employed to derive reliability indices including distribution functions of system lifetime and residual lifetime, together with expected operating time of the protective device. Moreover, two age-based replacement policies together with a condition-based replacement policy are developed to accommodate different maintenance scenarios and corresponding optimal solutions are acquired. Numerical illustrations based on the application of cooling systems in engines are presented to validate the results.

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Enabling Service Cache in Edge Clouds

ACM Transactions on Internet of Things ◽

10.1145/3456564 ◽

2021 ◽

Vol 2 (3) ◽

pp. 1-24

Author(s):

Chih-Kai Huang ◽

Shan-Hsiang Shen

Keyword(s):

Virtual Machines ◽

Replacement Policy ◽

Cache Replacement ◽

Cache Replacement Policy ◽

Average Latency ◽

Hit Rates ◽

Iot Devices ◽

Multi Access ◽

Computational Resources ◽

The Cost

The next-generation 5G cellular networks are designed to support the internet of things (IoT) networks; network components and services are virtualized and run either in virtual machines (VMs) or containers. Moreover, edge clouds (which are closer to end users) are leveraged to reduce end-to-end latency especially for some IoT applications, which require short response time. However, the computational resources are limited in edge clouds. To minimize overall service latency, it is crucial to determine carefully which services should be provided in edge clouds and serve more mobile or IoT devices locally. In this article, we propose a novel service cache framework called S-Cache , which automatically caches popular services in edge clouds. In addition, we design a new cache replacement policy to maximize the cache hit rates. Our evaluations use real log files from Google to form two datasets to evaluate the performance. The proposed cache replacement policy is compared with other policies such as greedy-dual-size-frequency (GDSF) and least-frequently-used (LFU). The experimental results show that the cache hit rates are improved by 39% on average, and the average latency of our cache replacement policy decreases 41% and 38% on average in these two datasets. This indicates that our approach is superior to other existing cache policies and is more suitable in multi-access edge computing environments. In the implementation, S-Cache relies on OpenStack to clone services to edge clouds and direct the network traffic. We also evaluate the cost of cloning the service to an edge cloud. The cloning cost of various real applications is studied by experiments under the presented framework and different environments.

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WRP: Weighting Replacement Policy to Improve Cache Performance

International Symposium on Computer Science and its Applications ◽

10.1109/csa.2008.61 ◽

2008 ◽

Cited By ~ 3

Author(s):

Kaveh Samiee ◽

GholamAli Rezai Rad

Keyword(s):

Replacement Policy ◽

Cache Performance

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On classes of life distributions based on the mean time to failure function

Journal of Applied Probability ◽

10.1017/jpr.2020.91 ◽

2021 ◽

Vol 58 (2) ◽

pp. 289-313

Author(s):

Ruhul Ali Khan ◽

Dhrubasish Bhattacharyya ◽

Murari Mitra

Keyword(s):

Damage Model ◽

Replacement Policy ◽

Time To Failure ◽

Mean Time To Failure ◽

Moment Convergence ◽

Life Distributions ◽

Cumulative Damage Model ◽

The Mean ◽

Age Replacement ◽

Mean Time

AbstractThe performance and effectiveness of an age replacement policy can be assessed by its mean time to failure (MTTF) function. We develop shock model theory in different scenarios for classes of life distributions based on the MTTF function where the probabilities $\bar{P}_k$ of surviving the first k shocks are assumed to have discrete DMTTF, IMTTF and IDMTTF properties. The cumulative damage model of A-Hameed and Proschan [1] is studied in this context and analogous results are established. Weak convergence and moment convergence issues within the IDMTTF class of life distributions are explored. The preservation of the IDMTTF property under some basic reliability operations is also investigated. Finally we show that the intersection of IDMRL and IDMTTF classes contains the BFR family and establish results outlining the positions of various non-monotonic ageing classes in the hierarchy.

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