International Journal of Reliability and Safety (20 papers in press)
Random finite element method for bearing capacity assessment of a shallow foundation under varied uniaxial loadings
by Amal Hentati, Mbarka Selmi, Tarek Kormi, Nizar Bel Hadj Ali
Abstract: This paper focuses on the application of the random finite element method (RFEM) for the assessment of the uniaxial bearing capacities of a shallow foundation subjected to centred vertical, horizontal and rotational loadings. The analysis combines finite element modelling, spatial variability analysis and Monte Carlo simulation. For this, the soil undrained shear strength is assumed to be variable in both horizontal and vertical directions with spatial dependency expressed via a Markovian autocorrelation function. The application of the proposed methodology to a shallow foundation permitted to highlight the insufficiency of the deterministic approach to predict the uniaxial foundation bearing capacities and led to different failure mechanisms.
Keywords: random finite element method; random fields; spatial variability; shallow foundation reliability.
Bayesian networks and probability boxes to model uncertainty in unavailability assessment
by Walid Mechri, Wassim Snene, Kamel Ben Othman
Abstract: In this article, the problem of uncertainty in assessing the unavailability of Safety Instrumented Systems (SIS) is treated. The characteristic parameters of the SIS, including common cause failure factors, are replaced by probability densities families (p-boxes) allowing reliability experts to express their uncertainty on the statement of value probabilities. We show how the imprecision is modelled and propagated in a Bayesian network, which induces uncertainty about the failure probability on demand of the SIS and its safety integrity level. We will demonstrate how the uncertainty on some characteristic parameters values causes significant variations on the level risk.
Keywords: safety systems; probability of failure on demand; uncertainty; Bayesian networks; common cause failure; p-boxes.
A prediction interval approach to developing life test acceptance criteria for progressively censored data
by Maram Salem, Zeinab Amin, Moshira Ismail
Abstract: In this paper we use the prediction-interval approach to construct acceptance criteria to determine whether or not certain batches of products are acceptable. The procedure is intended to protect us against highly defective lots and demonstrate that a required quality level is met with certain confidence. The prediction interval approach is particularly useful to employ when the lifetime of the product represents the quality characteristic of interest. On the basis of a progressively censored sample from the Weibull lifetime distribution, the problem of constructing acceptance criteria by predicting a future lifetime based on an independent past sample of lifetimes from the same distribution is addressed in a Bayesian setting with a dependent bivariate prior. The Metropolis-within-Gibbs sampler algorithm is used to obtain a sequence of draws from the posterior predictive distribution of future observations. This sequence is used to derive the prediction intervals based on which the lot acceptance criteria are determined. An example using real data is illustrated.
Keywords: acceptance criteria; Metropolis-within-Gibbs sampler algorithm; prediction interval; progressively censored sample; Weibull lifetime model.
Availability optimization of Pre Heat Exchanger system with random repair and failure rates using PSO
by Ajay Kumar
Abstract: The main objective of this study is to carry out performance analysis and availability maximization with randomly selected failure and repair rates (FRR) of a Pre Heat Exchanger (PHE) system of a brewery plant using the Particle Swarm algorithm. The behavioral analysis of each system is carried out by Markovian method and the schematic diagram of Pre Heat Exchanger system represents various components and their connectivity (series/parallel/hybrid) whereas the transition diagram explores various possibilities and combinations of working states of the components i.e. full capacity working (FCW), reduced capacity working (RCW) and failed state (FS). The mathematical equations are formulated using the transition diagrams in order to carry out steady state availability (SSA) and transient state availability (TSA) analysis. The prediction of failure and repair rate to attain maximum availability of a system is done by using Particle Swarm Optimization (PSO) technique. These results are beneficial for plant personnel by steering of failure and repair rates to achieve maximum availability in plant.
Keywords: Performance Modelling; Repair rates; Availability Optimization; Brewery Plant; Failure rate.
Reliability analysis of ((e, f), k, lc)/(m, n):F system under multiple failure using universal generating function
by Km. Meenakshi, S.B. Singh
Abstract: In this paper, the ((e, f),k, lc)/(m, n):F system is taken for study under multiple failures. The target system has m and n rows and columns, respectively. The system fails if any (e, f) submatrices fail or any k components fail, or consecutive lc components within any m rows or n columns fail out of (m, n) matrix. A Markov stochastic process is applied to obtain the probability of components of the system. Reliability indices such as reliability, mean time to failure and sensitivity analysis of the considered system are evaluated with the help of universal generating function. Finally, a numerical example is taken to demonstrate the model.
Keywords: ((e; f),k; lc)/(m; n):F system; reliability; mean time to failure; sensitivity analysis; universal generating function.
Performance assessment of repairable system in series configuration under different types of failure and repair policies using copula linguistics
by Monika Gahlot, V.V. Singh, Hamisu Ismial Ayagi, C.K. Goel
Abstract: This paper deals with the study of reliability measures of a complex system consisting of two subsystems, subsystem-1 and subsystem-2, in a series configuration. The subsystem-1 has three units that work under the policy 2-out-of-3: F; and the subsystem-2 has two units working under 1-out-of-2: G; policy. Failure rates of the units of subsystems are constant and assumed to follow an exponential distribution, but the repair supports two types of distribution, general distribution and Gumbel- Hougaard family copula distribution. Two types of repair (general repair and Copula repair) are employed for partially failed and completed failed states. The system is analysed using the supplementary variable technique. Some important measures of reliability, such as the availability of the system, the reliability of the system, (MTTF) and profit analysis are discussed. Computations have taken a particular case by evaluating availability, reliability, MTTF and profit of operation of the system.
Keywords: k-out-of-n: F; system; k-out-of-n: G; system; availability; MTTF; cost analysis; Gumbel-Hougaard family copula distribution.
Model-checking software product line based on multi-valued logic
by Shuang Liu, Yufeng Shi, Mingyu Huang
Abstract: A software product line (SPL) maximises commonality between software products to reduce cost and improve productivity. In this paper, we consider model-checking partial software product line designs. We first propose bilattice-based feature transitions systems (BFTSs) for modelling partial SPL designs, which support description of uncertainty and preserve features as a first class notion; the partial model and final model of product are defined via projection and simulation. We then express system behavioral properties using ACTL formulas and define its semantics over BFTSs. We investigate model-checking software product lines based on bilattice in two efficient ways: we provide the procedures that translate BFTSs to multi-valued Kripke structure and develop a software model-checker assistant BPMCA to leverage the power of the existing model-checking engine called XChek for verification; we decompose the multivalued BFTS into three-valued BFTS. Finally, we implement our approach on a benchmark from the literature.
Keywords: model checking; software product line; multi-valued.
A fuzzy-QFD approach for the enhancement of work equipment safety: a case study in the agriculture sector
by Mario Fargnoli, Mara Lombardi, Nicolas Haber
Abstract: The paper proposes a design for safety methodology based on the use of the Quality Function Deployment (QFD) method, focusing on the need to identify and analyse risks related to a working task in an effective manner, i.e. considering the specific work activities related to such a task. To reduce the drawbacks of subjectivity while augmenting the consistency of judgements, the QFD was augmented by both the Delphi method and the fuzzy logic approach. To verify such an approach, it was implemented through a case study in the agriculture sector. While the proposed approach needs to be validated through further studies in different contexts, its positive results in performing hazard analysis and risk assessment in a comprehensive and thorough manner can contribute practically to the scientific knowledge on the application of QFD in design for safety activities.
Keywords: design for safety; risk assessment; hazard analysis; quality function deployment; fuzzy logic; agricultural machinery.
Bayesian sample size determination for product retesting after design change in Poisson-distributed data
by Swapnil Khorate, Digambar Shirke
Abstract: Many times, design is changed after product validation testing in the design world. It occurs more frequently in the engineering field, which will create a problem of retesting the product with original product specification without consideration of degree and significance of the design change. As far as cost and resources are concerned, we have to find minimum sample size for retesting the product. In this article, we present a Bayesian method for determining sample size for retesting the redesigned product in Poisson-distributed data via prior success-based testing. Numerical results of sample size for retesting the redesigned product are given. An example of paper pulp is provided.
Keywords: Bayesian analysis; retesting; gamma priors; redesign; Poisson distribution; sample size reduction.
State-control-limit-based rejuvenation modelling and optimisation of the virtualised cloud server
by Weichao Dang, Jianchao Zeng
Abstract: Software rejuvenation modelling and optimisation of the virtualised cloud server has been studied. A software rejuvenation policy on the virtual machines and the virtual machine monitor is proposed in order to ensure high availability of the virtualised cloud server. The multi-component system, composed of the virtual machines and the virtual machine monitor, which are structurally dependent, is reduced to the multiple two-component systems. A state-control-limit-based rejuvenation policy is proposed, and the joint probability density of the degraded state of the two-component VM-VMM is derived. Furthermore, the solution to the joint probability density is proposed. Finally, the stationary unavailability of the virtualised cloud server is modelled. Numerical experiments have verified the correctness of the probability density function and the feasibility of the rejuvenation policy. The state-control-limit-based rejuvenation policy leads to lower unavailability of the virtualised cloud server in comparison with the lifetime-based rejuvenation policy.
Keywords: software rejuvenation; state-control-limit; virtualised cloud server; availability.
Bearing health assessment based on Hilbert transform envelope analysis and cluster analysis
by Xin Zhang, Jianmin Zhao, Xianglong Ni, Fucheng Sun, Haiping Li
Abstract: In this paper, the improved K-means clustering analysis is used to evaluate the bearing health state. The high-pass filter and Hilbert transform envelope analysis are used to enable the original signal to become smooth and gentle, so as to reduce the influence of noise. The combination of three feature parameters is chosen to evaluate the bearing health state. The extracted feature parameters are clustered by using K-means algorithm. The degradation state of the bearing can be recognised by cluster analysis. In this paper, there are two case studies are provided to verify the effectiveness of the method.
Keywords: cluster analysis; bearing; Hilbert transform; envelope analysis; high-pass filter.
Special Issue on: Engineering Design for Safety and Reliability
Topology optimisation design of mechanical tee backsheet
by Wang Jinlong, Chen Junlong
Abstract: A finite element model of ASTM 114.3 mechanical tee backsheet is established by using the finite element software ANSYS. The stress distribution of the backsheet under pretension force load is obtained through the strength analysis, and based on this,a topology optimisation calculation of the backsheet is analysed. According to the topology optimisation results, the backsheet structure is redesigned and finite element analysis showed that, by reducing the volume of the model of the backsheet while improving its stress distribution, the maximum equivalent stress is reduced and the chip reliability is enhanced.
Keywords: mechanical tee backsheet; finite element analysis; topology optimisation; optimal design.
Reliability assessment of pressure vessel design methods
by Hongjun Li, Peng Yang, Xun Huang, Hui Yang
Abstract: Several pressure vessel design methods based on elastic analysis and elastic-plastic analysis are available to designers. This paper proposes a reliability analysis method to assess three pressure vessel design methods: stress categorisation method, limit-load analysis in ASME code, and DBA-L method, which was recently proposed by the present authors. It was concluded that, with the same input variables into the three analyses, the responses of calculated results of the three methods were different, which provided an effective guidance to assess and choose the proper design method in engineering practice.
Keywords: pressure vessel design; reliability; stress categorisation method; limit-load analysis method.
Multi-state system reliability analysis methods based on Bayesian networks, merging dynamic and fuzzy fault information
by Qin He, Ruijun Zhang, Tianyu Liu, Jie Liu
Abstract: Traditional Bayesian networks (BNs) have limited abilities to analyse system reliability with fuzzy and dynamic information. To deal with such information in system reliability analysis, a new multi-state system reliability analysis method based on BNs is proposed. The method expands the traditional BNs and effectively solves the deficiencies of existing reliability analysis methods based on BNs incorporating fuzziness and fault information. In this work, fuzzy set theory and changing failure probability function of components are introduced into BNs, and the concept of dynamic fuzzy subsets is introduced. The curve of the fuzzy dynamic fault probability of the leaf node fault state and fuzzy dynamic importance are developed and calculated with MATLAB software. Finally, a case study of a truck system is employed to demonstrate the performance of the proposed methods in comparison with traditional fault tree analysis methods and T-S fuzzy importance analysis methods. The proposed methods proved to be feasible in capturing the fuzzy and dynamic information in real-world systems.
Keywords: fuzzy subsets; fuzziness; Bayesian network; travel system of a truck.
Reliability allocation technique for complex system of systems
by Antony Gratas Varuvel
Abstract: Reliability allocation is one of the important tasks during the design phase, which is to be executed as part of DfR practices. There are many techniques published in the literature for the stated purpose. Appropriate methodology is chosen based on the data available and the factors of influence required to be considered. Among those, the AGREE method is one of the reliability allocation techniques that is widely adopted during the early stages of the product/project definition. The popularity of this model is attributed to the assumption of standard exponential failure rate distribution, which is the simplest and easiest among the statistical failure rate distributions. Despite this, the AGREE method fails to meet the target reliability, when any/many of the importance index[es] is/are less than unity, resulting in impractical allocation of reliability. In addition, the assumption of exponential probability density function, which is the basis of the AGREE method stands valid only to depict failures arising out of randomness in the physical/environmental behaviour resulting in failures. Hence, validity and appropriateness of the AGREE
method for a complex system of systems [SoS], wherein electronics, mechanical, and electromechanical systems are to be allocated, cease to converge. Subjectivity involved with the methodology published recently on reliability allocation procedure in complex redundant systems is greater, which leads to inconsistent results. This paper aims to eliminate the shortcomings of both the methods, which are enumerated. Representing the complex SoS and generalisation of a universal model that could be adapted to any domain, for the purposes of reliability allocation during the initial phases of design are the main objectives that are set forth, while conceptualising the model. Verification of the model under various boundary conditions has been carried out. Although the proposed model is aimed for general usage, it has been validated with the available data in the aerospace domain. Results obtained are found to be achieving the target goal set for the platform, which is a complex SoS.
Keywords: AGREE; allocation; failure rate; fighter aircraft; maintainability; MTBF; MTTF; reliability.
New component-based reliability model to predict the reliability of component-based software
by Dimpal Tomar, Pradeep Tomar
Abstract: Component-based software technology has potential impact on the evolution of software development. One of the dominant questions while designing Component-Based Software (CBS) is to preserve its quality in which reliability has a crucial part. Therefore, prognosis of the reliability of a component-based software system is difficult because mostly components are of black type so the prediction of the emergent properties, such as reliability, is particularly difficult. In this paper, we propose a reliability estimation model noted as Component-Based Reliability Model (CBRM) to assess the reliability of individual components, and after integration of components, i.e. based on two factors: component reliability and average number of interaction failures.
Keywords: component-based software reliability; CBSS; interaction ratio.
Risk-energy aware service level agreement assessment for computing quickest path in computer networks
by Ashutosh Sharma, Rajiv Kumar
Abstract: In this paper, a new variant of the quickest path problem (QPP) is addressed with additional factors of risk and energy, which leads to the evaluation of risk-energy constrained quickest path problem (REQPP) computation. In REQPP, risk is based on lag-time or delay and energy necessary for the transmission between two adjacent nodes. The formulation of this problem presents a realistic path computation for the critical applications. Success of REQPP is measured by defining a service level agreement (SLA). The proposed algorithm is able to solve the risk-energy constrained quickest path problem for the continuity of communication. SLA fulfills the needs of multi-constrained path whereas its time-complexity is of the order of the Dijkstras algorithm. Finally, variation of penalty time and risk variation helps to find the high-performance value of the allowed delay time toward success of SLA.
Keywords: green communications; risk-energy constraints; quickest path problem; requested service level agreements.
Emergency braking mechanism for an elevator using hydraulic and pneumatic actuation
by Krutarth Mehta, Nitin Rohatgi, Parijat Sarkar, Christo Michael Tharsis
Abstract: The proposed idea aims at replacing the current safety mechanisms used by the elevators (i.e. governors) which are rope-based safety mechanism to rope-independent, actuated by pneumatic and hydraulic cylinders. The proposed safety mechanism is lightweight and mounted on the top of the elevator. The mechanism involves a pneumatic cylinder actuating a hydraulic master cylinder using a class 1 lever for mechanical advantage. The hydraulic cylinder will pressurise the brake fluid and supply it to the calipers mounted on the elevator body. Calipers will cling to the guide rails upon actuation, thus stopping the elevator in a very short distance. The effective force to be stopped by the calipers was calculated and parts were designed accordingly. Analyses of parts are done by considering maximum forces acting on hydraulic caliper mount and lever arm for varying thickness. Through calculations and analyses, the proposed system was found to be safe and reliable.
Keywords: safety mechanism; elevator; pneumatic cylinder; hydraulic master cylinder; class 1 lever; guide rail; hydraulic caliper mount; lever arm.
A hybrid fault tolerance framework for SaaS services based on hidden Markov model
by Feng Ye, Qian Huang, Zhijian Wang, Ling Li
Abstract: With the booming of cloud computing, more and more applications adopt cloud services to implement their critical business. However, failures causing either service downtime or producing invalid results in such applications may range from a mere inconvenience to significant monetary penalties or even loss of human lives. In critical systems, making the cloud services highly dependable is one of the main challenges. Existing researches show that using fault injection for experimental assessment of fault tolerance architecture for cloud services is still an open problem because of the complexity and diversity of failures in cloud environment. Therefore, we propose a hybrid fault tolerance framework that uses replication and design diversity techniques for SaaS service. In order to verify the effectiveness of the fault tolerance framework in various pragmatic failure scenarios, a mixed fault simulator based on urn and ball model in the hidden Markov model is introduced. A series of experiments are carried out for evaluating the reliability of the SaaS service, including single service without replication, single service with retry or reboot, and a service with spatial replication. The results show that the mixed fault simulator is flexible for simulating various faults in cloud environment, and both temporal and spatial redundancy have better effect on the availability and reliability improvement of the SaaS service.
Keywords: hidden Markov model; SaaS; fault tolerance; cloud services.
The probabilistic analysis of fatigue crack effect based on magnetic flux leakage
by Meor Qram Meor Ahmad, A. Arifin, S. Abdullah, W.Z.W. Jusoh, S.S.K. Singh
Abstract: In this paper, probabilistic analysis on the fatigue crack effect was investigated by applying the Metal Magnetic Memory (MMM) method, based on Self-Magnetic Leakage Field (SMLF) signals on the surface of metal components. The precision of MMM signals is essential in identifying the validity of the proposed method. The tension-tension fatigue test was conducted using the testing frequency of 10 Hz with 4 kN loaded, and the MMM signals were captured using the MMM instrument. As a result, a linear relationship was observed between the magnetic flux leakage and cyclic loading parameter, presenting the R-squared value at 0.72 0.97. The 2P-Weibull distribution function was used as a probabilistic approach to identify the precision of the data analysis from the predicted, and experimental fatigue lives, thereby showing that all points are placed within the range of a factor of 2. Additionally, the characteristics of PDF, CDF, failure rate and failure probability data analysis were plotted and described. Therefore, a 2P-Weibull probability distribution approach is determined to be an appropriate method to determine the accuracy of data analysis for MMM signals in a fatigue test for metal components.
Keywords: MMM signals; fatigue lives; Weibull distribution.