Reliability Measures Of System Research Articles

Study of reliability measures of a local area network via copula linguistics approach

Purpose – The purpose of this paper is to find the reliability measures of Linux operating system connected in local area network (LAN). Design/methodology/approach – The system has two different topologies, i.e. star topology (subsystem-1) and bus topology (subsystem-2), are placed at two different places, and connected to a server through a hub. Both the topologies have n clients. The system has partial failure and complete failure. The partial failure is of two type’s namely minor partial and major partial. The minor partial failure degrades the system whereas the major partial failure brings the system to a break down mode. The system can completely fail due to failure of server hacking and blocking. Findings – By using supplementary variable technique and Laplace transformation, by taking different types of failure and two types of repairs the availability, non-availability, mean time to failure and cost analysis (expected profit) of the design system have been obtained. Originality/value – In this research, a mathematical model of Linux operating system has been discussed from which one can check the behavioral analysis of the designed system.

Reliability measures of a computer system with priority to PM over the H/W repair activities subject to MOT and MRT

Article history: Received September 18, 2014 Accepted 15 December 2014 Available online December 16 2014 This paper concentrates on the evaluation of reliability measures of a computer system of twoidentical units having independent failure of h/w and s/w components. Initially one unit is operative and the other is kept as spare in cold standby. There is a single server visiting the system immediately whenever needed. The server conducts preventive maintenance of the unit after a maximum operation time. If server is unable to repair the h/w components in maximum repair time, then components in the unit are replaced immediately by new one. However, only replacement of the s/w components has been made at their failure. The priority is given to the preventive maintenance over repair activities of the h/w. The time to failure of the components follows negative exponential distribution whereas the distribution of preventive maintenance, repair and replacement time are taken as arbitrary. The expressions for some important reliability measures of system effectiveness have been derived using semi-Markov process and regenerative point technique. The graphical behavior of the results has also been shown for a particular case. Growing Science Ltd. All rights reserved. 5 © 201

Transient Analysis of ak-out-of-n:GSystem withN-Policy, Repairmen’s Multiple Vacations, and Redundant Dependency

This paper analyzes ak-out-of-n:Grepairable system withN-policy, repairmen’s multiple synchronous vacations, and redundant dependency. When there is no failed component in the system, the repairmen leave for a vacation, the duration of which follows a phase type distribution. Upon returning from vacation, they should take another vacation if there are less thanNfailed components waiting in the system. This pattern continues until at leastNfailed components are waiting. Moreover, the redundant dependency which is a special kind of failure dependency is taken into account in the multicomponent system. Under such assumptions, the availability, the rate of occurrence of failures, and the reliability of the system are derived in transient regime by applying the quasi-birth-and-death process. Furthermore, the Runge-Kutta method is carried out to numerically discuss the time-dependent behavior of the system reliability measures. Finally, a special case of the system is presented to show the validity of our model.

Reliability Measures of a Two-Unit Cold Standby Repairable System with Priority to Operation over Preventive Maintenance

main objective of present work is to carry out various important reliability measures of a twounit cold s tandby repairable system with priority to operation over preventive maintenance by using regenerative points technique and semiMarkov process. A single repair facility is pr ovided to conduct repair and maintenance of the system as and when required. All times distributions are exponential except the repair and preventive maintenance time distributions which are considered as general.

Spatiotemporal variation of long‐term drought propensity through reliability‐resilience‐vulnerability based Drought Management Index

AbstractThis paper characterizes the long‐term, spatiotemporal variation of drought propensity through a newly proposed, namely Drought Management Index (DMI), and explores its predictability in order to assess the future drought propensity and adapt drought management policies for a location. The DMI was developed using the reliability‐resilience‐vulnerability (RRV) rationale commonly used in water resources systems analysis, under the assumption that depletion of soil moisture across a vertical soil column is equivalent to the operation of a water supply reservoir, and that drought should be managed not simply using a measure of system reliability, but should also take into account the readiness of the system to bounce back from drought to a normal state. Considering India as a test bed, 5 year long monthly gridded (0.5° Lat × 0.5° Lon) soil moisture data are used to compute the RRV at each grid location falling within the study domain. The Permanent Wilting Point (PWP) is used as the threshold, indicative of transition into water stress. The association between resilience and vulnerability is then characterized through their joint probability distribution ascertained using Plackett copula models for four broad soil types across India. The joint cumulative distribution functions (CDF) of resilience and vulnerability form the basis for estimating the DMI as a five‐yearly time series at each grid location assessed. The status of DMI over the past 50 years indicate that drought propensity is consistently low toward northern and north eastern parts of India but higher in the western part of peninsular India. Based on the observed past behavior of DMI series on a climatological time scale, a DMI prediction model comprising deterministic and stochastic components is developed. The predictability of DMI for a lead time of 5 years is found to vary across India, with a Pearson correlation coefficient between observed and predicted DMI above 0.6 over most of the study area, indicating a reasonably good potential for drought management in the medium term water resources planning horizon.

Efficient analysis of multi-state k-out-of-n systems

Many practical systems are multi-state k-out-of-n systems with independent, non-identical components, where the system and its components have multiple performance levels and maybe multiple failure modes. Furthermore the system may have different requirements on the number of working components (i.e., value of k) for different system state levels. This paper proposes a new analytical method based on multi-valued decision diagrams (MDDs) for the reliability analysis of such multi-state k-out-of-n systems. MDDs have recently been applied to the reliability analysis of general multi-state systems (MSS). In this work, we make the new contribution by proposing a novel and efficient algorithm for constructing the system MDD that is designed to fully make use of the well-defined k-out-of-n structure. Examples show how the MDD models are generated using the proposed algorithm, and are then evaluated to obtain the system reliability measures. Performance of the MDD-based method is compared with that of an existing recursive algorithm through a comprehensive benchmark study. Empirical results show that the proposed MDD-based method can offer lower computational complexity than the recursive algorithms, and it can be effectively applied to large practical cases for multi-state k-out-of-n systems.

Reliability analysis of a repairable system with geometric reneging and threshold-based recovery policy

This article attempts to investigate the reliability measures of a repairable system with [Formula: see text] identical operating units, [Formula: see text] standby units, and a repairman. The repairman is subject to breakdowns and operates threshold-based recovery policy. As soon as the repairman breaks down, the repair does not start immediately until the number of failed units in the system reaches a specified threshold value [Formula: see text]. When the repairman is working or broken down, failed units arriving for maintenance may renege and decide sequentially whether to leave the queue or not. The failed times of operating and standby units, maintenance times and reneging time of failed units, and breakdown and repair times of the repairman are all assumed to be exponential distributions. We develop the system reliability and mean time to system failure. Through numerical results, sensitivity analysis is carried out to assess the impact of various system parameters on the system reliability and mean time to system failure. Finally, an application example is given to evaluate the reliability measures of an electric power system.

Reliability analysis of a k-out-of-n:G repairable system with single vacation

This paper analyzes a k-out-of-n:G repairable system with one repairman who takes a single vacation, the duration of which follows a general distribution. The working time of each component is an exponentially distributed random variable and the repair time of each failed component is governed by an arbitrary distribution. Moreover, we assume that every component is “as good as new” after being repaired. Under these assumptions, several important reliability measures such as the availability, the rate of occurrence of failures, and the mean time to first failure of the system are derived by employing the supplementary variable technique and the Laplace transform. Meanwhile, their recursive expressions are obtained. Furthermore, through numerical examples, we study the influence of various parameters on the system reliability measures. Finally, the Monte Carlo simulation and two special cases of the system which are (n-1)-out-of-n:G repairable system and 1-out-of-n:G repairable system are presented to illustrate the correctness of the analytical results.

On the effect of near-field excitations on the reliability-based performance and design of base-isolated structures

This work explores the effect of near-field excitations on the reliability-based performance and design of base-isolated systems. In particular base-isolated buildings under uncertain excitation are considered in this work. A probabilistic logic approach is adopted for considering the variability of future excitations. Isolation elements composed by rubber bearings are used in the present formulation. The non-linear behavior of the bearings is characterized by a biaxial hysteretic model which is calibrated with experimental data. The performance of the isolated system is defined in terms of the isolators deformations and the superstructure interstory drifts and absolute accelerations. First excursion probabilities are used as measures of system reliability. Two example problems involving large finite element building models are presented to illustrate the ideas set forth.

Transient analysis of hardware and software systems with warm standbys and switching failures

Redundancy or standby is a provision which plays an important role in improving the reliability of engineering systems. This investigation deals with the reliability and sensitivity analysis of a repairable system (consisting of hardware and software components) with warm standbys and switching failures. The failure and repair rates of the components are assumed to follow exponential distributions. By using Markovian property, the transient state model is developed to establish the system reliability and other performance measures. Numerical technique-based matrix method is used to compute various system performance indices. A numerical example is provided to illustrate the tractability of the proposed method.

RELIABILITY MEASURES OF A COLD STANDBY SYSTEM WITH PREVENTIVE MAINTENANCE AND REPAIR

The purpose of the present study is to determine reliability measures of a two-unit cold standby system with preventive maintenance and repair. The units are identical in nature subject to constant failure from normal mode. Preventive maintenance of the operative unit is carried out after a pre-specific time "t" up to which no failure occurs. However, repair of the unit is done at its failure. The unit works as new after repair and preventive maintenance. The switch devices are perfect. The distributions of failure time and the time by which unit undergoes for preventive maintenance are taken as negative exponential while that of preventive maintenance and repair times are assumed as arbitrary with different probability density functions. The random variables associated with failure, preventive maintenance and repair times are statistically independent. The semi-Markov process and regenerative point technique are adopted to derive the expressions for system performance measures in steady state. The graphical behavior of MTSF, availability and profit function have been observed with respect to preventive maintenance rate for particular values of other parameters and costs.

The semi-Markov model of the process of appearance of sea-going ship propupsion system ability and inability states in application to determining the reliablity of these systems

ABSTRACT The article presents possible application of the theory of semi-Markov processes in creating the eight-state model of the process of appearance of the propulsion systems ability and inability states on sea-going vessels performing transportation tasks in a relatively long operating time t (t → ∞). The model has been proved to be able to be successfully used for determining the reliability of the abovementioned systems. The probability of faultless operation in time t was assumed the measure of system reliability. Operating situations of sea-going vessels were characterised, with special attention being paid to the fact that the loads of propulsion system components of these vessels are of random nature. These loads lead to damages which for this reason were also considered random events. It was also assumed that the damages provoke the appearance of states of inability of particular ship propulsion system components which means that these states are random events as well. The states of ability of a given ship propulsion system have been assumed to exist when all components of this system are in the state of ability. In case when at least one component is in the state of inability, the entire system is in the state of inability. Conditions were formulated for the reliability model of an arbitrary system to be able to be worked out in the form of the semi-Markov process. The need for the use of technical diagnostics in reliability examination of sea-going ship propulsion systems was indicated. In conclusions, certain qualities of the article were highlighted which are, in author’s opinion, of highest importance in reliability examination of sea-going ship propulsion systems.

Generation maintenance scheduling using improved binary particle swarm optimisation considering aging failures

This study presents a coordinated deterministic and stochastic framework for maintenance scheduling (MS) of generators, using improved binary particle swarm optimisation (IBPSO). Fundamental concern of MS is to reduce the generator failures and to extend the generator lifespan, thereby increases the system reliability. The IBPSO finds an optimal schedule for the generators and overcome the drawbacks of the conventional methods. The objective of this study is to reduce the loss of load probability and minimising the annual supply reserve ratio deviation for a power system, which are considered as a measure of power system reliability. Moreover, in this study the impacts of aging failures of the generators are considered in order to calculate the unavailability of power system which is modelled using the Weibull distribution. The proposed algorithm is tested on IEEE reliability test system. Comprehensive study has also been carried out in the context of Kerala (India) power system. It can accomplish a significant levelisation in the reliability indices over the maintenance planning period and demonstrates the potential to solve the MS problem. The numerical results are obtained using the proposed method, which outperforms other compared techniques such as genetic algorithm, particle swarm optimisation, binary particle swarm optimisation methods and conventional methods.

Strategy for Synthesis of Flexible Heat Exchanger Networks Embedded with System Reliability Analysis

System reliability can produce a strong influence on the performance of the heat exchanger network (HEN). In this paper, an optimization method with system reliability analysis for flexible HEN by genetic/simulated annealing algorithms (GA/SA) is presented. Initial flexible arrangements of HEN is received by pseudo-temperature enthalpy diagram. For determining system reliability of HEN, the connections of heat exchangers(HEXs) and independent subsystems in the HEN are analyzed by the connection sequence matrix(CSM), and the system reliability is measured by the independent subsystem including maximum number of HEXs in the HEN. As for the HEN that did not meet system reliability, HEN decoupling is applied and the independent subsystems in the HEN are changed by removing decoupling HEX, and thus the system reliability is elevated. After that, heat duty redistribution based on the relevant elements of the heat load loops and HEX areas are optimized in GA/SA. Then, the favorable network configuration, which matches both the most economical cost and system reliability criterion, is located. Moreover, particular features belonging to suitable decoupling HEX are extracted from calculations. Corresponding numerical example is presented to verify that the proposed strategy is effective to formulate optimal flexible HEN with system reliability measurement.

Reliability modeling of a single-unit system with arbitrary distributions subject to different weather conditions

The main concentration of the present study is on the evaluation of some important reliability measures of a single-unit system considering arbitrary distributions for the random variables associated with failure and repair times, time to change of weather conditions, inspection time and arrival time of the server. The system operates under two weather conditions-normal and abnormal. The unit fails completely via partial failure. There is a single server who takes some time to arrive at the system. Server inspects the unit at its complete failure to see the feasibility of its repair while repair of the unit at partial failure is done without inspection. The unit works as new after repair at partial failure whereas unit is assumed as degraded after repair at complete failure. Inspection of the degraded unit is also conducted at its failure to examine the feasibility of repair. The degraded unit is replaced by new one if inspection reveals that its repair is not feasible to the system. Some measures of system effectiveness are obtained using semi-Markov and regenerative point technique. Giving particular values to various parameters and costs, the numerical results for mean time to system failure, availability and profit function are obtained considering exponential and Rayleigh distributions for all random variables.

Metrics for Assessing the Reliability of a Telemedicine Remote Monitoring System

The goal of this study was to assess using new metrics the reliability of a real-time health monitoring system in homes of older adults. The "MobileCare Monitor" system was installed into the homes of nine older adults >75 years of age for a 2-week period. The system consisted of a wireless wristwatch-based monitoring system containing sensors for location, temperature, and impacts and a "panic" button that was connected through a mesh network to third-party wireless devices (blood pressure cuff, pulse oximeter, weight scale, and a survey-administering device). To assess system reliability, daily phone calls instructed participants to conduct system tests and reminded them to fill out surveys and daily diaries. Phone reports and participant diary entries were checked against data received at a secure server. Reliability metrics assessed overall system reliability, data concurrence, study effectiveness, and system usability. Except for the pulse oximeter, system reliability metrics varied between 73% and 92%. Data concurrence for proximal and distal readings exceeded 88%. System usability following the pulse oximeter firmware update varied between 82% and 97%. An estimate of watch-wearing adherence within the home was quite high, about 80%, although given the inability to assess watch-wearing when a participant left the house, adherence likely exceeded the 10 h/day requested time. In total, 3,436 of 3,906 potential measurements were obtained, indicating a study effectiveness of 88%. The system was quite effective in providing accurate remote health data. The different system reliability measures identify important error sources in remote monitoring systems.

System resiliency quantification using non-state-space and state-space analytic models

Resiliency is becoming an important service attribute for large scale distributed systems and networks. Key problems in resiliency quantification are lack of consensus on the definition of resiliency and systematic approach to quantify system resiliency. In general, resiliency is defined as the ability of (system/person/organization) to recover/defy/resist from any shock, insult, or disturbance [1]. Many researchers interpret resiliency as a synonym for fault-tolerance and reliability/availability. However, effect of failure/repair on systems is already covered by reliability/availability measures and that of on individual jobs is well covered under the umbrella of performability [2] and task completion time analysis [3]. We use Laprie [4] and Simoncini [5]'s definition in which resiliency is the persistence of service delivery that can justifiably be trusted, when facing changes. The changes we are referring to here are beyond the envelope of system configurations already considered during system design, that is, beyond fault tolerance. In this paper, we outline a general approach for system resiliency quantification. Using examples of non-state-space and state-space stochastic models, we analytically–numerically quantify the resiliency of system performance, reliability, availability and performability measures w.r.t. structural and parametric changes.

Reliability Estimation and Confidence-interval for Two-unit System in the Presence of Common Cause Failures and Human Errors

This paper discusses the estimation of reliability measures of two unit system with identical components in the presence of chance Common Cause Shock (CCS) failures as well as human errors. The Maximum likelihood (M L) approach has been followed for the present model. The M L estimates of system reliability measures like reliability function[R(t)], mean time between failures (MTBF) were developed. The estimates were derived for both series and parallel systems. We also developed the confidence interval for the present study. The empirical evidence was developed by using Monte-Carlo simulation for selected values of the failure and repair rates to establish the validity and precision of the M L estimates of the above said reliability measures.

Hybrid improved binary particle swarm optimization approach for generation maintenance scheduling problem

This paper presents a model for maintenance scheduling (MS) of generators using hybrid improved binary particle swarm optimization (IBPSO) based coordinated deterministic and stochastic approach. The objective function of this paper is to reduce the loss of load probability (LOLP) and minimizing the annual supply reserve ratio deviation for a power system which are considered as a measure of power system reliability. Genetic algorithm (GA) operators are introduced in the IBPSO to acquire diversified solutions in the search space. Moreover, in this paper, the hybrid IBPSO based economic dispatch (ED) has been decomposed as a sub-problem in the maintenance model that results to a more practical maintenance schedule. A case study for the real power system model in Odisha (India) is considered. Comprehensive studies have also been carried out for the different power system consisting of 5-unit system, 21-unit system and IEEE reliability test system (RTS). It shows that the proposed algorithm can accomplish a significant levelization in the reliability indices over the planning horizon for reliable operation of the power system and demonstrates the usefulness of the proposed approach. The proposed method yields better result by means of improved search performance and better convergence characteristics which are compared to the other optimization methods and conventional method.

Estimation of the Reliability Measures of a Three-component System with Human Errors and Common Cause Failures

present paper discusses the problem of estimating the reliability measures of a three-component identical system when the system is affected by Common Cause Shock (CCS) failures as well as human errors. The maximum likelihood estimators of the reliability measures like reliability function and mean time between failures of the present model are obtained. The performances of the proposed estimates have been developed in terms of mean square error, using simulated data.