Redundant Subsystems Research Articles

Optimal redundancies of parallel–series systems in irrelevancy coverage model

A common method for increasing the reliability of a system is to introduce redundant components. However, when the coverage of a fault is imperfect, the system may fail prior to the exhaustion of spares because of noncovered component failures, and an excessive level of redundancy may reduce rather than improve the system reliability. This study investigates the optimal redundancy of parallel–series systems in an irrelevancy coverage model (ICM), which is an extension of the imperfect fault coverage model (IFCM). Three different optimal strategies are studied in ICM, namely optimal redundancies for reliability maximization, cost minimization, and both. Experimental results demonstrate that the optimal redundancies in the ICM are different from those in the IFCM, and the ICM can accommodate more redundant subsystems for parallel–series systems to achieve higher reliability and lower cost than the IFCM in general.

Reliability Modeling and Maintenance Optimization for a Repairable System With Heterogeneity Population

This article proposes an integrated approach for reliability modeling and maintenance scheduling of repairable parallel systems subject to hidden failures. The system consists of heterogeneous redundant subsystems whose failures are detected only by inspections. Inspections at periodic times reveal the components state, and repair actions are decided by the excursion of a basic state process describing the total number of failed components (deterioration level) in each subsystem. Using the standard renewal arguments, this article aims at minimizing the average cost rate by the joint determination of the optimal inspection interval <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\tau$</tex-math></inline-formula> and maintenance parameters <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\kappa$</tex-math></inline-formula> (partial repair threshold) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> (preventive replacement threshold). We illustrate the procedure for the case as the components’ lifetimes conform to the Weibull distribution. The proposed model and the response of the optimal solutions to the model’s parameters are illustrated through numerical examples. The approach outlined here allows exploring different scenarios and further extensions.

An innovative FDIR approach for the power supply of the PRETTY SDR satellite payload

CubeSat missions are characterized by short development times and challenging budget constraints. Due to the constraints in terms of mass, volume, and power, it is often not possible to increase reliability by adding redundant subsystems to the spacecraft. Therefore, it is necessary to implement important error-proofing mechanisms to still be able to derive a high scientific benefit from these missions. Once the satellite has been launched, physical access to the satellite’s hardware is no longer possible. For this reason, systems are often implemented that allow automatic failure detection, isolation of the failure from other systems, as well as automatic recovery (FDIR). This paper describes the advantages and areas of application of software-defined radio platforms (SDRs) on board of small satellites and CubeSats. In addition, important aspects of the hardware FDIR concept of the PRETTY SDR payload system are presented. In order to prevent the hardware from being damaged with a fault-free power supply, different levels of fault monitoring are described as well.

Improving CubeSat reliability: Subsystem redundancy or improved testing?

The objective of this paper is to investigate which approach would lead to more reliable CubeSats: full subsystem redundancy or improved testing. Based on data from surveys, the reliability of satellites and subsystems is estimated using a Kaplan–Meier estimator. Subsequently, a variety of reliability models is defined and their maximum likelihood estimates are compared. A product of a Lognormal distribution addressing immaturity failure and a Gompertz distribution addressing wear-out is found to best represent CubeSat reliability. Bayesian inference is used to find realistic wear-out parameters by using failure data of small satellites. Subsystem reliability estimates are subsequently found using a similar approach. A reliability model for CubeSats with redundant subsystems is established, verified and applied in a Monte Carlo simulation. The results are compared with a model for reduced immaturity failure. Allocating resources to reduction of immaturity failures through improved testing is considered to be superior to allocating these resources to the implementation of subsystem redundancy.

Resilient redundancy-based control of cyber–physical systems through adaptive randomized switching

A switching based approach using multiple parallel redundant controller implementations is developed to improve resiliency of cyber–physical systems (CPSs). Hardware/software redundancy is known to be a powerful technique for resiliency to mitigate effects of adversaries who infiltrate and maliciously modify a subset of the redundant subsystems. While redundant subsystems are typically combined using fail-over/backup and voting mechanisms, the proposed approach considers a time-division multiplexer using which one of multiple controller implementations is selected at each time instant to drive the input of the controlled system. Through detailed analysis of the switched system, it is shown that time-division multiplexing between redundant controllers can be used to mitigate the impact to stability and/or performance of the closed-loop CPS due to adversarial modifications of subsets of controllers. Additionally, we show that adversarial impact to the closed-loop CPS can be reduced over time by switching among the controllers in a probabilistic manner (rather than round-robin) and by dynamically adapting probabilities of switching to each controller. The efficacy of the proposed adaptive randomized switching algorithm is shown through simulation studies on two illustrative examples: a simple third-order system and a more real-world single-machine-infinite-bus system.

Reliability evaluation of a k-out-of-n(G)-subsystem based multi-state phased mission system with common bus performance sharing subjected to common cause failures

Multi-state phased mission systems (MS-PMSs) with common bus performance sharing widely exist in practice. Their subsystems are often designed as redundant k-out-of-n(G) systems to ensure the reliable operation of the whole system, such as power generating systems. However, common cause failures (CCFs) of components can decrease the reliability of such redundant subsystems. Considering the above two factors, we propose a new reliability model for the MS-PMS with k-out-of-n(G) subsystems and performance sharing subject to CCFs. Each subsystem contains multiple multi-state components, whose behaviors are analyzed using the Markov chain. Components in each subsystem may belong to a CCF group, and each CCF group suffers multiple independent CCF modes. We propose a Binary Indicator Universal Generating Function (BIUGF) method to evaluate the system reliability by adding an indicator variable and a pointer vector in the traditional universal generating function method, and the impacts of CCFs are taken into account using an implicit analysis method. The method is illustrated and validated through applications to power supply systems, which justify the effectiveness of the proposed method.

Overview of the Solar Radiation and Climate Experiment (SORCE) Seventeen-Year Mission

The Solar Radiation and Climate Experiment (SORCE) was a NASA mission that operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). Three important accomplishments of the SORCE mission are i) the continuation of the 42-year-long TSI climate data record, ii) the continuation of the ultraviolet SSI record, and iii) the initiation of the near-ultraviolet, visible, and near-infrared SSI records. All of the SORCE instruments functioned well over the 17-year mission, which far exceeded its five-year prime mission goal. The SORCE spacecraft, having mostly redundant subsystems, was also robust over the mission. The end of the SORCE mission was a planned passivation of the spacecraft following a successful two-year overlap with the NASA Total and Spectral Solar Irradiance Sensor (TSIS) mission, which continues the TSI and SSI climate records. There were a couple of instrument anomalies and a few spacecraft anomalies during SORCE’s long mission, but operational changes and updates to flight software enabled SORCE to remain productive to the end of its mission. The most challenging of the anomalies was the degradation of the battery capacity that began to impact operations in 2009 and was the cause for the largest SORCE data gap (August 2013 – February 2014). An overview of the SORCE mission is provided with a couple of science highlights and a discussion of flight anomalies that impacted the solar observations. Companion articles about the SORCE instruments and their final science data-processing algorithms provide additional details about the instrument measurements over the duration of the mission.

RAP via hybrid genetic simulating annealing algorithm

This paper aims to solve Redundancy allocation problem (RAP). It is a significant complex optimization and non-linear integer programming problem of reliability engineering. RAP includes the choices of components and the suitable amount of redundant subsystems for maximizing reliability of the system under given restrictions like cost, weight, volume etc. It is difficult to solve non-linear complex problems. In this paper, the RAP is solved by the combination of genetic and simulating algorithm that is called Hybrid Genetic Simulating Annealing Algorithm (HGSAA). It can be observed that superiority of both the algorithms are combined and form an adequate algorithm which ignores the individual weakness. Comparative analysis of HGSAA with existing methods such as Heuristic Algorith, Constraint Optimization Genetic Algorithm, Hybrid Particle Swarm Optimization and Constraint Optimization Genetic Algorithm are presented in this study. RAP is also solved by Branch and Bound method to validate the result of HGSAA. The developed algorithm is programmed by Matlab.

Исследование способов повышения безотказности пассивно резервированных подсистем управления летательными аппаратами с учетом допусков

The paper studies the reliability of passively redundant subsystems of aircraft, taking into account tolerances for a decrease in their output parameters in case of sudden component failures. The influence of the reliability values of elements, tolerances of two levels and the redundancy ratio &#x0D; on the reliability of passively redundant subsystems as a whole have been investigated; the examples of such subsystems have been given. There have been presented the results of analysis &#x0D; of the aircraft subsystems features with allowance for tolerances. First of all, these include the availability of technical specifications and realized tolerances determined by the reservation structure; implementing each tolerance with different values of the multiplicities of redundancy; using the main tolerance grid by multiple backup methods; presence of critical probabilities narrowing the reliability range of the elements, where this type of reservation is beneficial from the range &#x0D; 0–1 to the range of the supercritical area (pkr–1). The influence of the element reliability values, tolerances of two levels and the redundancy ratio on the failure-free operation of passively redundant subsystems in general and in supercritical areas has been investigated. It is shown that the minimum redundancy multiplicities in the interests of increasing the reliability of the considered subsystems of aircraft are advantageous to use only with large tolerances and low probabilities of failure-free operation of their elements. Under close tolerances and any reliability values of elements, as well as with large tolerances (more than 25%), high reliability values of this class of aircraft subsystems can be achieved only with large redundancy multiplicities. It has been inferred that there are extreme reliability differences of a passively redundant subsystem and its element, which &#x0D; allows to set the task of developing highly reliable passively redundant subsystems of aircraft taking into account tolerances from relatively unreliable elements.

Factor of Security (FoS): Quantifying the Security Effectiveness of Redundant Smart Grid Subsystems

According to IEC 61850-90-4, most smart grid substations are designed with redundancy in order to improve their availability in case of failures. Redundancy usually takes the form of having multiple subsystems with identical functionality based on the assumption that failures in one subsystem are isolated from other subsystems. However, this is not necessarily true in the case of failures caused by malicious attacks, because attackers can easily reuse their skills and tools across different subsystems under similar configurations. Taking this into consideration, this paper introduces the factor of security (FoS) metrics to quantify the security effectiveness of redundant subsystems in smart grids. Specifically, we first apply the attack graph model to capture various threats in smart grids and substations; we then formally define the FoS metric and the probabilistic FoS metric; finally, we evaluate those metrics under different scenarios through simulations.

Availability Analysis of a Repairable Series-Parallel System with Redundant Dependency

This paper investigates the steady-state availability of a repairable series-parallel system with redundant dependency. The different types of components and repairmen are taken into account, the failure rate of the operating component varies as the number of other failed components and the repair rate of the failed component is constant in each parallel redundant subsystem. To quantify the redundant dependency, a modified failure dependence function is introduced to determine the failure rate of the components in each subsystem. Markov theory and matrix analysis method are used to get the steady-state probability vector of each subsystem and the steady-state availability of the entire system. A numerical example is presented to illustrate the obtained results and to analyze the effect of redundant dependency class on the system availability.

Multi-objective optimization of reliability-redundancy allocation problem for multi-type production systems considering redundancy strategies

This paper innovatively proposes a new model of multi-type production system which can process different types of production. The multi-type production system consists of several independent sequentially ordered subsystems which undertaking different tasks. Different types of production require different manufacturing lines: required subsystems will be powered on, while others powered off. The system can switch into different production line based on detection results. A binary matrix is suggested to describe the composition of each production line of the multi-type production system. Reliability-redundancy allocation on each subsystem is considered for achieving higher reliabilities of different production lines. The reliability-redundancy allocation problem for the proposed multi-type production system is essentially multi-objective subject to resource constraints. This paper formulates the multi-objective optimization problem and considers the optimal redundancy strategy, either active or cold standby. The exact reliabilities of cold standby redundant subsystems with imperfect detector/switch are determined by introducing an approach based on continuous time Markov chain. Then, a multi-objective evolutionary algorithm is suggested to solve the proposed reliability-redundancy allocation problem. Finally, numerical examples are presented to illustrate the proposed methods.

Synthesis of structure of the onboard passive redundant subsystem with due consideration of the established tolerances

The goal of this article is to select optimal parameters of various structures of the passive redundant subsystems of flying vehicles (hereinafter to be referred to as the “the aircraft”) with due consideration of the established tolerances in respect of decrease in output parameters of these subsystems in the cases of failure of the aircraft components (in accordance with the required failure-free operation). It was demonstrated that synthesis of such structure is based on the solving the two-objective optimisation problem, which can be reduced to the one-criterion problem with the help of various methods. Authors of this article have selected the linear convolution method. Due to the absence of information on quantitative values of the prescribed tolerances and on the required failure-free operation of actual subsystems, authors have performed calculations of relevant dependences within the wide range of the realisable tolerances of the first and second levels. Authors have investigated influence of values of the required failure-free operation and values of tolerances upon the optimal structure of the passive redundancy subsystems of the aircraft.

CONSIDERATION OF SIGNIFICANT FACTORS AND LIMITATIONS IN THE STUDY AND DEVELOPMENT OF PASSIVELY RESERVED AIRCRAFT SUBSYSTEMS, TAKING INTO ACCOUNT TOLERANCES

Objectives.The relevance of this article lies in the fact that the problem of increasing the reliability of subsystems of aviation and rocket and space technology in case of sudden independent refusals determines one of the important areas of scientific research. The work is aimed at identifying and analyzing specific features that must be considered when researching and developing passively redundant subsystems, taking into account tolerances in case of sudden independent failures.Method.During the study, calculations were carried out using the methods of probability, search. The necessity of taking into account assigned and implemented tolerances, multiple and non-multiple reservation, discrete scales of realizable tolerances with different levels of significance, critical probabilities, determining the probability ranges of elements, where redundancy is profitable and unprofitable, is shown.Result.The possibility of implementing any tolerance for different values of a number of increasing individual multiplicities is revealed, which allows for a given tolerance to pose the task of finding the optimal multiplicity and its corresponding optimal backup structure in the interests of ensuring maximum reliability of the redundant subsystems. Analysis of the presented dependencies for the implemented tolerances of the first and second levels shows that for each tolerance level there are equilibrium values ???????????? at which the critical values of p_kr practically do not change depending on the multiplicities ????????.Conclusion. A different nature of the change in the critical probabilities ???????????? was found depending on the multiplicities for different values of the tolerances to be realized. So, with tolerances of the first level, larger than 25%, with increasing multiplicity, p_kr increases and smaller than 25% decreases with increasing multiplicity. The similar nature of the change in the p_kr values has a 28.6% tolerance for the implemented second-level tolerances.

Probabilistic Analysis of a Ceramic Tile Production System Considering Various Redundant Subsystems and Inspection

The present paper gives analysis of a stochastic model for a ceramic tile production system considering its five main subsystems viz. Ball Mill, Spray Dryer, Hydraulic Press, Glaze Line and Kiln and a storage system, Silo. It was considered that the failure of Ball Mill and Spray Dryer subsystems depends upon Silo while failure of other subsystems are independent of Silo. Also the storage in Silo is consumed during the repair/replacement of the failed subsystems then the system goes to failure otherwise it is operative. During the occurrence of failure in subsystems Hydraulic Press, Glaze Line and Kiln, leads to the failure in other subsequent subsystem and the repairman first inspects in which redundant unit of the subsystem has a fault and then accordingly repair/replacement is carried out. The system has been analysed using Markov process and regenerative point techniques. Various conclusions for the system regarding its reliability and availability are drawn by plotting several graphs for a particular case.

Rare Event Simulation to Optimise Maintenance Intervals of Safety Critical Redundant Subsystems

In the railway sector, many redundant subsystem structures are applied to increase the safety and availability of the overall railway system. Failures to single paths of these structures occur and are found during routine inspection. Routine inspections are, depending on their type and the equipment location, quite costly and limit the vehicle availablity. The present paper analyses occurrences based on simulated data resembling field data of a fleet of rail vehicles. The system is analysed statistically to identify the wear mechanisms leading to the failures. Failure data is then used to identify wear models which are consequently used in a Markov Chain (MC) to simulate the probability of multiple path failure. The failure rate of the overall system is typically expected to be in the range $\left(10^{-9}\cdots10^{-6}\right)\, \mathrm{h}^{-1}$ due to the safety critical nature of the railway system. For this reason, it is required to apply rare event simulation techniques to the MC simulation in order to limit the number of simulations. The simulation results are then applied to an optimisation of the inspection routine, which yields an appropriate failure rate for the associated hazards.

Variation-Aware Reliable Many-Core System Design by Exploiting Inherent Core Redundancy

Reliability issues are more severe in multi/many-core systems because of the integration of more devices in advanced technology nodes. To achieve robust computing in nanoscale designs, many circuit-level and architecture-level redundancy techniques had been proposed, which pose large fixed silicon area overhead and a lack of flexibility. In recent years, some methods have exploited the “inherent core redundancy” of many-core systems to implicitly implement N-modular redundant (NMR) subsystems to achieve area-efficient fault-tolerant computing. However, while facing the different levels of soft error rate, task vulnerability, and task significance in the many-core system, existing core-level redundancy methods become ineffective. To achieve robust computation in many-core systems with intercore variations and mixed workloads, we propose a variation-aware core-level redundancy scheme. Two novel approaches are presented in this scheme: 1) we construct NMR tables that store the degree of redundancy using mathematical models for systems affected by these variations and 2) we dynamically allocate each replicated task to a proper core with variation-aware mapping algorithms to achieve high reliability. Based on a modified multicore simulator, Sniper-Transient Error Process Variation (TEVR), the experimental results show that the proposed scheme can increase the reliability by 47.92% and achieve the energy saving of 39% compared with conventional core-level redundancy methods.

Improving the reliability and availability of railway track switching by analysing historical failure data and introducing functionally redundant subsystems.

Track switches are safety critical assets that not only provide flexibility to rail networks but also present single points of failure. Switch failures within dense-traffic passenger rail systems cause a disproportionate level of delay. Subsystem redundancy is one of a number of approaches, which can be used to ensure an appropriate safety integrity and/or operational reliability level, successfully adopted by, for example, the aeronautical and nuclear industries. This paper models the adoption of a functional redundancy approach to the functional subsystems of traditional railway track switching arrangements in order to evaluate the potential increase in the reliability and availability of switches. The paper makes three main contributions. First, 2P-Weibull failure distributions for each functional subsystem of each common category of points operating equipment are established using a timeline and iterative maximum likelihood estimation approach, based on almost 40,000 sampled failure events over 74,800 years of continuous operation. Second, these results are used as baselines in a reliability block diagram approach to model engineering fault tolerance, through subsystem redundancy, into existing switching systems. Third, the reliability block diagrams are used with a Monte-Carlo simulation approach in order to model the availability of redundantly engineered track switches over expected asset lifetimes. Results show a significant improvement in the reliability and availability of switches; unscheduled downtime reduces by an order of magnitude across all powered switch types, whilst significant increases in the whole-system reliability are demonstrated. Hence, switch designs utilising a functional redundancy approach are well worth further investigation. However, it is also established that as equipment failures are engineered out, switch reliability/availability can be seen to plateau as the dominant contributor to unreliability becomes human error.

Reliability–redundancy allocation problem considering optimal redundancy strategy using parallel genetic algorithm

To maximize the reliability of a system, the traditional reliability–redundancy allocation problem (RRAP) determines the component reliability and level of redundancy for each subsystem. This paper proposes an advanced RRAP that also considers the optimal redundancy strategy, either active or cold standby. In addition, new examples are presented for it. Furthermore, the exact reliability function for a cold standby redundant subsystem with an imperfect detector/switch is suggested, and is expected to replace the previous approximating model that has been used in most related studies. A parallel genetic algorithm for solving the RRAP as a mixed-integer nonlinear programming model is presented, and its performance is compared with those of previous studies by using numerical examples on three benchmark problems.

Multi-Objective Optimization of a Complex System using GPSIA+DS

In this study, an efficient biologically inspired constrained multi-objective optimization algorithm called Genetic Pareto Set Identification Algorithm plus Different Sex (GPSIA+DS) was developed. A complex system comprising of mixed configuration, k-out-of-n and redundant subsystem was used to validate GPSIA+DS in comparison with Genetic Pareto Set Identification Algorithm (GPSIA) and Fast Non–Dominated Sorting Genetic Algorithm plus Constrain Domination (NSGA-II+CD). The optimization strategy based on Genetic Pareto Set Identification Algorithm (GPSIA) only considered feasible solutions. That is, solutions, which satisfies all constraints conditions. Infeasible solutions could facilitate faster convergence to the true Pareto front. GPSIA+DS, which considers feasible and infeasible solutions in it optimization strategy was shown to outperform GPSIA and NSGA-II for the test problem considered.