Strategic defense and attack for reliability systems

This article illustrates a method by which arbitrarily complex series/parallel reliability systems can be analyzed. The method is illustrated with the series–parallel and parallel–series systems. Analytical expressions are determined for the investments and utilities of the defender and the attacker, depend on their unit costs of investment for each component, the contest intensity for each component, and their evaluations of the value of system functionality. For a series–parallel system, infinitely many components in parallel benefit the defender maximally regardless of the finite number of parallel subsystems in series. Conversely, infinitely many components in series benefit the attacker maximally regardless of the finite number of components in parallel in each subsystem. For a parallel–series system, the results are opposite. With equivalent components, equal unit costs for defender and attacker, equal intensity for all components, and equally many components in series and parallel, the defender always prefers the series–parallel system rather than the parallel–series system, and converse holds for the attacker. Hence from the defender's perspective, ceteris paribus, the series–parallel system is more reliable, and has fewer “cut sets” or failure modes.     

Reliability analysis of mining equipment: A case study of a crushing plant at Jajarm Bauxite Mine in Iran

The performance of mining machines depends on the reliability of the equipment used, the operating environment, the maintenance efficiency, the operation process, the technical expertise of the miners, etc. As the size and complexity of mining equipments continue to increase, the implications of equipment failure become ever more critical. Therefore, reliability analysis is required to identify the bottlenecks in the system and to find the components or subsystems with low reliability for a given designed performance. It is important to select a suitable method for data collection as well as for reliability analysis. This paper presents a case study describing reliability and availability analysis of the crushing plant number 3 at Jajarm Bauxite Mine in Iran. In this study, the crushing plant number 3 is divided into six subsystems. The parameters of some probability distributions, such as Weibull, Exponential, and Lognormal distributions have been estimated by using ReliaSoft's Weibull++6 software. The results of the analysis show that the conveyer subsystem and secondary screen subsystem are critical from a reliability point of view, and the secondary crusher subsystem and conveyer subsystem are critical from an availability point of view. The study also shows that the reliability analysis is very useful for deciding maintenance intervals.     

Approximate Reliability and Availability Models for High Availability and Fault‐tolerant Systems with Repair

Systems designed for high availability and fault tolerance are often configured as a series combination of redundant subsystems. When a unit of a subsystem fails, the system remains operational while the failed unit is repaired; however, if too many units in a subsystem fail concurrently, the system fails. Under conditions usually met in practical situations, we show that the reliability and availability of such systems can be accurately modeled by representing each redundant subsystem with a constant, ‘effective’ failure rate equal to the inverse of the subsystem mean‐time‐to‐failure (MTTF). The approximation model is surprisingly accurate, with an error on the order of the square of the ratio mean‐time‐to‐repair to mean‐time‐to‐failure (MTTR/MTTF), and it has wide applicability for commercial, high‐availability and fault‐tolerant computer systems. The effective subsystem failure rates can be used to: (1) evaluate the system and subsystem reliability and availability; (2) estimate the system MTTF; and (3) provide a basis for the iterative analysis of large complex systems. Some observations from renewal theory suggest that the approximate models can be used even when the unit failure rates are not constant and when the redundant units are not homogeneous. Copyright © 2004 John Wiley & Sons, Ltd.     

Spacecraft electrical power subsystem: Failure behavior, reliability, and multi-state failure analyses

This article investigates the degradation and failure behavior of spacecraft electrical power subsystem (EPS) on orbit. First, this work provides updated statistical reliability and multi-state failure analyses of spacecraft EPS and its different constituents, namely the batteries, the power distribution, and the solar arrays. The EPS is shown to suffer from infant mortality and to be a major driver of spacecraft unreliability. Over 25% of all spacecraft failures are the result of EPS failures. As a result, satellite manufacturers may wish to pursue targeted improvement to this subsystem, either through better testing or burn-in procedures, better design or parts selection, or additional redundancy.Second, this work investigates potential differences in the EPS degradation and failure behavior for spacecraft in low earth orbits (LEO) and geosynchronous orbits (GEO). This analysis was motivated by the recognition that the power/load cycles and the space environment are significantly different in LEO and GEO, and as such, they may result in different failure behavior for the EPS in these two types of orbits. The results indicate, and quantify the extent to which, the EPS fails differently in LEO and GEO, both in terms of frequency and severity of failure events. A casual summary of the findings can be stated as follows: the EPS fails less frequently but harder (with fatal consequences to the spacecraft) in LEO than in GEO.     

Effects of Common Structural Rules on hull-girder reliability of an Aframax oil tanker

This paper aims at quantifying the changes in notional reliability levels that result from redesigning an existing Aframax tanker to comply with the Common Structural Rules (CSR) for double-hull oil tankers. The probability of structural failure is calculated using the first-order reliability method. The evaluation of the wave-induced load effects that occur during long-term operation of the ship in the seaway is carried out in accordance with the International Association of Classification Societies (IACS)-recommended procedure, while transfer functions are calculated using the sink–source 3D linear method. The still-water loads are defined on the basis of a statistical analysis of loading conditions from the loading manual. The ultimate collapse bending moment of the midship cross section, which is used as the basis for the reliability formulation, is evaluated by progressive collapse analysis and by a single-step procedure according to CSR. The reliability assessment is performed for “as-built” and “corroded” states of the existing ship and a reinforced ship complying with CSR. It is shown that the hull-girder failure probability of an Aframax tanker is reduced several times due to the reinforcements according to CSR. Sensitivity analysis and a parametric study are performed to investigate the variability of results with the change of parameters of pertinent random variables within their plausible ranges. Finally, differences between load combination approaches by Ferry-Borges and Castanheta method and Turkstra's rule are investigated.     

On the value of redundancy subject to common-cause failures: Toward the resolution of an on-going debate

Common-cause failures (CCF) are one of the more critical and challenging issues for system reliability and risk analyses. Academic interest in modeling CCF, and more broadly in modeling dependent failures, has steadily grown over the years in the number of publications as well as in the sophistication of the analytical tools used. In the past few years, several influential articles have shed doubts on the relevance of redundancy arguing that “redundancy backfires” through common-cause failures, and that the latter dominate unreliability, thus defeating the purpose of redundancy. In this work, we take issue with some of the results of these publications. In their stead, we provide a nuanced perspective on the (contingent) value of redundancy subject to common-cause failures. First, we review the incremental reliability and MTTF provided by redundancy subject to common-cause failures. Second, we introduce the concept and develop the analytics of the “redundancy–relevance boundary”: we propose this redundancy–relevance boundary as a design-aid tool that provides an answer to the following question: what level of redundancy is relevant or advantageous given a varying prevalence of common-cause failures? We investigate the conditions under which different levels of redundancy provide an incremental MTTF over that of the single component in the face of common-cause failures. Recognizing that redundancy comes at a cost, we also conduct a cost–benefit analysis of redundancy subject to common-cause failures, and demonstrate how this analysis modifies the redundancy–relevance boundary. We show how the value of redundancy is contingent on the prevalence of common-cause failures, the redundancy level considered, and the monadic cost–benefit ratio. Finally we argue that general unqualified criticism of redundancy is misguided, and efforts are better spent for example on understanding and mitigating the potential sources of common-cause failures rather than deriding the concept of redundancy in system design.     

Demonstration of statistical approaches to identify component's ageing by operational data analysis—A case study for the ageing PSA network

The paper presents some results of a case study on “Demonstration of statistical approaches to identify the component's ageing by operational data analysis”, which was done in the frame of the EC JRC Ageing PSA Network. Several techniques: visual evaluation, nonparametric and parametric hypothesis tests, were proposed and applied in order to demonstrate the capacity, advantages and limitations of statistical approaches to identify the component's ageing by operational data analysis. Engineering considerations are out of the scope of the present study.     

The thermal control system

This paper presents the design, analysis and performance of the thermal control system ofAryabhata. A passive thermal control system, using flat absorber-AK-512 black paint for the outer surface of the satellite and a combination of solar reflector-AK-512 white paint and mechanical polishing for the inner surfaces, was employed to maintain the temperature of all the electronics subsystems onboard the satellite within the specified limits of 0°C and 40°C during the operational life of the satellite. The in-flight temperature data obtained from sixteen temperature sensors onboard the satellite was compared with the theoretically predicted temperature values and the agreement was good for all electronic subsystems housed within the framework of the satellite. The observed deviations in temperature for the tape recorder, proportional counter package and gas bottles of the spin-up system are attributed to the assumptions made for the mathematical model. It has been found that by improving these approximations, the deviations could be reduced to negligible values.     

Mission reliability analysis of fault-tolerant multiple-phased systems

Fault-tolerant multiple-phased systems (FTMPS) are defined as systems whose critical components are independently replicated and whose operational life can be partitioned into a set of disjoint periods, called “phases”. Because of their deployment in critical applications, their mission reliability analysis is a task of primary relevance to validate the designs. This paper is focused on the reliability analysis of FTMPS with random phase durations, non-exponentially distributed repair activities and different repair policies. For self-repairable FTMPS with a component-level reconfiguration architecture, we derive several efficient formulations from the underlying structure characteristics for their intraphase behavior analysis. We also present a uniform solution framework of the mission reliability for FTMPS with generally distributed phase durations. Compared with existing methods based on deterministic and stochastic Petri nets or Markov regenerative stochastic Petri nets, our approach is more simple in concept and powerful in computation. Two examples of FTMPS are analyzed to illustrate the advantages of our approach.     

Functional failure analysis of a thermal–hydraulic passive system by means of Line Sampling

Assessing the failure probability of a thermal–hydraulic (T–H) passive system amounts to evaluating the uncertainties in its performance. Two different sources of uncertainties are usually considered: randomness due to inherent variability in the system behavior (aleatory uncertainty) and imprecision due to lack of knowledge and information on the system (epistemic uncertainty).In this paper, we are concerned with the epistemic uncertainties affecting the model of a T–H passive system and the numerical values of its parameters. Due to these uncertainties, the system may find itself in working conditions that do not allow it to accomplish its functions as required. The estimation of the probability of these functional failures can be done by Monte Carlo (MC) sampling of the epistemic uncertainties affecting the model and its parameters, followed by the computation of the system function response by a mechanistic T–H code.Efficient sampling methods are needed for achieving accurate estimates, with reasonable computational efforts. In this respect, the recently developed Line Sampling (LS) method is here considered for improving the MC sampling efficiency. The method, originally developed to solve high-dimensional structural reliability problems, employs lines instead of random points in order to probe the failure domain of interest. An “important direction” is determined, which points towards the failure domain of interest; the high-dimensional reliability problem is then reduced to a number of conditional one-dimensional problems which are solved along the “important direction”. This allows to significantly reduce the variance of the failure probability estimator, with respect to standard random sampling.The efficiency of the method is demonstrated by comparison to the commonly adopted Latin Hypercube Sampling (LHS) and first-order reliability method (FORM) in an application of functional failure analysis of a passive decay heat removal system in a gas-cooled fast reactor (GFR) of literature.     

Operating Environment-Based Availability Importance Measures for Mining Equipment (Case Study: Sungun Copper Mine)

When a system’s performance is inadequate, the concept of availability importance can be used to improve it. The availability of an item depends on the combined aspects of its reliability and maintainability. In a system consisting of many subsystems, the availability of some subsystems is more important to system performance than others. The availability measure determines the priority of availability across subsystems. Most researchers only consider operation time and ignore the influence of the operating environment; therefore, their estimations are not accurate enough. In contrast to previous research, we focus on the influence of the operating environment on the system/subsystem’s characteristics with a view to prioritizing them based on the importance of availability. The paper considers part of the mining fleet system of Sungun copper mine, including the wagon drill, loader, bulldozer, and dump truck subsystems. We identify an ordered list of possibilities for availability improvement and suggest changes or remedial actions for each item to either reduce its failure rate or reduce the time required to repair it.     

System repairs: When to perform and what to do

In this paper an indicator is used that reflects the “state” of a system as a function of the ages of the (groups of) subsystems of which it consists. The contribution of the ages of the subsystems to the state of the system is defined by their weights. The indicator can be interpreted as the virtual age of the system, and can therefore be used to define age-reduction factors of different types of repair in a virtual age or age-reduction process. The state indicator is used as the time scale in a proportional intensity model. In this way, the joint impact of different repair strategies and covariates on the system failure intensity can be evaluated. This relationship is then used to address the question of which subsystems to replace whenever a system comes in for repair and when to set the preventive inspection/repair interval, in order to minimize the expected costs per unit time until the next inspection and/or repair. A numerical and a practical example are given.     

Multitarget-tracking optical processing system

We consider multitarget tracking, estimating the state vector (two-dimensional position and velocity) of each target from physical measurements. We consider a full system for this and the role for analog optical processing within its subsystems. We emphasize the neural network data-association subsystem (which associates measurements in the present input frame with estimates from previous frames of data). Our new optimization neural net results concern associations between measurements and estimates and show that use of a simple fixed-coefficient estimation filter is sufficient. For completeness in our full system approach we briefly describe our optical detection subsystem and its use to reduce frame-to-frame jitter in the measurements. We also briefly note our Hough-transform optical subsystem and discuss its use in detecting and correcting data dropout errors and errors in the data-association and estimator systems. We conclude that analog optical processing has significant use in a full multitarget tracking system.     

The fast alternative cryogenic experiment testbed

Subsystems for a “proof of concept” cryogenic payload have been developed to demonstrate the ability to accommodate low temperature science investigations within the constraints of the Hitchhiker siderail (HH-S) carrier on the Space Shuttle. These subsystems include: a hybrid solid neon – superfluid helium cryostat, a multi-channel Versa Modular European (VME) architecture Germanium Resistance Thermometer (GRT) readout and heater control servo system, and a multiple thermal isolation stage “probe” for thermal control of helium samples. The analysis and tests of these subsystems have proven the feasibility of a cryogenic HH-S carrier payload.     

Parametric and nonparametric inference for the reliability of copula-based stress-strength models

This paper provides a general treatment of statistical inference for the reliability in copula-based stress-strength models. Most of the current literature is either focused on specific models that yield clean formulas or restricted to estimation and engineering aspects without addressing statistical inference. We present two general frameworks, one parametric, one nonparametric, for the estimation of the reliability. The parametric methodology is presented under the general framework of estimating equations, mostly as a combination of existing methodologies from the fields of multivariate analysis, reliability, and econometrics, with some new results. The nonparametric methodology is a novel application based on an existing bivariate kernel method combined with Monte Carlo estimation of the reliability without specification of the copula or the margins. We present results from a small simulation study designed to assess the robustness of the methods discussed in terms of model misspecification. We used geotechnical data and data from the Brazilian Household Survey to illustrate the proposed methodologies in the estimation of factors of safety and financial fragility.     

Reliability Analysis and Evaluation of Differential System Based on low Load Strengthening Model

The differential is an important part of a driveline, and differential performance is related to the handling and stability performance of a vehicle. Thus, a differential with sound design structure and reasonable form and size parameters could lead to satisfactory driving performance. In this work, we analyze and evaluate the reliability of the key parts of a differential system. Firstly, each of key parts is regarded as a subsystem of a differential system, so the subsystem reliability models are obtained. A system reliability model is built based on the paths of the forces from the differential system, and system reliability is calculated. Secondly, according to the result of the analysis of system reliability and the use of the six sigma method, 45 steel or 1Cr18Ni9Ti utilized as the material for the worm shaft, system reliability is analyzed and discussed separately. Then, the reliability of the key parts and the overall system reliability increase with the low load strengthening characteristic of the material. Finally, according to the analysis and discussion, the level of system reliability matches that required for differential systems, and the cost is also considerably reduced, as demonstrated using the stress–strength interference and low‐load strengthening models. These results provide a theoretical basis for the improvement of the design of Torsen differentials. Similar methods can be used to develop automobile subsystems in the future. Copyright © 2015 John Wiley & Sons, Ltd.     

Research on multiple-state industrial robot system with epistemic uncertainty reliability allocation method

Reliability allocation of industrial robot (IR) system is one of the important means to improve its whole life cycle, reduce maintenance cost, and characterize weak subsystems. The IR system is not only very complex but also has strong customization; meanwhile, its sample data are small, resulting in unclear degeneration and failure. Based on the above two epistemic uncertainties, a new methodology called multiple-state IR system reliability allocation method with epistemic uncertainty (MIRS-RAM-EU) is proposed. First, the Dempster-Shafer (D-S) evidence theory is used to quantify the epistemic uncertainty. Then, the Kolmogorov differential equations of MIR's subsystems are calculated. The reliability index of MIRS is allocated based on Birnbaum importance degree theory, and the reliability allocation coefficient of each IR subsystem is clearly expressed by this method. Finally, compared with traditional importance allocation method, the MIRS-RAM-EU is more efficient and accurate. This method is usefully directive for reliability evaluation of IR.     

A parameter tree approach to estimating system sensitivities to parameter sets

A post-processing technique for determining relative system sensitivity to groups of parameters and system components is presented. It is assumed that an appropriate parametric model is used to simulate system behavior using Monte Carlo techniques and that a set of realizations of system output(s) is available. The objective of our technique is to analyze the input vectors and the corresponding output vectors (that is, post-process the results) to estimate the relative sensitivity of the output to input parameters (taken singly and as a group) and thereby rank them. This technique is different from the design of experimental techniques in that a partitioning of the parameter space is not required before the simulation. A tree structure (which looks similar to an event tree) is developed to better explain the technique. Each limb of the tree represents a particular combination of parameters or a combination of system components. For convenience and to distinguish it from the event tree, we call it the parameter tree.To construct the parameter tree, the samples of input parameter values are treated as either a “+” or a “−” based on whether or not the sampled parameter value is greater than or less than a specified branching criterion (e.g., mean, median, percentile of the population). The corresponding system outputs are also segregated into similar bins. Partitioning the first parameter into a “+” or a “−” bin creates the first level of the tree containing two branches. At the next level, realizations associated with each first-level branch are further partitioned into two bins using the branching criteria on the second parameter and so on until the tree is fully populated. Relative sensitivities are then inferred from the number of samples associated with each branch of the tree.The parameter tree approach is illustrated by applying it to a number of preliminary simulations of the proposed high-level radioactive waste repository at Yucca Mountain, NV. Using a Total System Performance Assessment Code called TPA, realizations are obtained and analyzed. In the examples presented, groups of five important parameters, one for each level of the tree, are used to identify branches of the tree and construct the bins. In the first example, the five important parameters are selected by more traditional sensitivity analysis techniques. This example shows that relatively few branches of the tree dominate system performance. In another example, the same realizations are used but the most important five-parameter set is determined in a stepwise manner (using the parameter tree technique) and it is found that these five parameters do not match the five of the first example. This important result shows that sensitivities based on individual parameters (i.e. one parameter at a time) may differ from sensitivities estimated based on joint sets of parameters (i.e. two or more parameters at a time).The technique is extended using subsystem outputs to define the branches of the tree. The subsystem outputs used in this example are the total cumulative radionuclide release (TCR) from the engineered barriers, unsaturated zone, and saturated zone over 10,000 yr. The technique is found to be successful in estimating the relative influence of each of these three subsystems on the overall system behavior.     

Reliability Reallocation for Fuel Cell Vehicles Based on Genetic Algorithm

A fuel cell vehicle (FCV) is a type of alternative energy vehicle that could help resolve the energy crisis, mitigate environmental problems, and contribute to sustainable development. Developing an FCV with high reliability is an important goal for automobile factories and research institutions. Other key factors required by FCVs include mass production and customer approval. An FCV is a complex mechanism composed of many subsystems. During the development of the overall vehicle, steps should be taken to ensure that every subsystem is reliable. However, such development must also consider costs, which must be kept as low as possible. To ensure the reliability of FCV while operating under conditions that demand minimal cost, a genetic algorithm is employed to reallocate the reliability of the overall vehicle system. First, the growth factor of the reliability–feasibility of each subsystem is determined according to the complexity, importance, and technological level of the FCV subsystems. The FCV cost model is then established on the basis of such parameters as subsystem cost, reliability–feasibility growth factor, initial reliability, limit reliability, and so on. A genetic algorithm is then used to compute for the reliability of FCV subsystems. The rationality of reliability reallocation is verified according to the subsystem importance coefficient. This method considers the benefits for both enterprises and customers by applying principles of engineering and conducting a reliability study. Copyright © 2014 John Wiley & Sons, Ltd.     

空间站可靠性定额设计

象空间站这样的大型航天器的可靠性问题是十分重要而又十分复杂的，本文仅就其可靠性问题中的定额部分进行了研究，以俄罗斯相关资料上的可靠性指标资料，载人航天器故障统计资料作为原型资料，对未来某型空间站的总体可靠性以及其站上系统的可靠性进行了定额设计。