International Journal of Reliability and Safety (13 papers in press)
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.
An optimal rejuvenation scheme for improving VoIP service reliability in the existence of resource exhaustion and security breaches
by Vandana Gupta, Rahul Kumar
Abstract: Voice over internet protocol (VoIP) is a progressive technology in the area of telecommunication. The escalating number of end-users of VoIP and the challenges faced in furnishing first-class quality of service (QoS) are the major driving force for research in the area of VoIP service up-gradation. When the resources allotted to every end-user gets exhausted, the resulting crisis can lead to either a decline in the QoS or a total loss of service. In addition, as VoIP is an application operating on the internet, it is prone to numerous security breaches. It is noteworthy to realise that VoIP is a comparatively young technology, and with any new technology, security naturally gets better with maturity. This paper addresses the issues of resource exhaustion and security breaches in a VoIP network, and is intended to analyse their combined effect on the QoS of VoIP. To help avert performance degradation and other associated failures in a VoIP system, and to improve its comprehensive reliability software rejuvenation procedure is performed. The performance of a VoIP system in the existence of resource exhaustion and security breaches is modelled by means of a continuous time Markov chain (CTMC) to study the system reliability. From the CTMC the mean time to failure (MTTF) is obtained as a system reliability measure. Furthermore, an optimal rejuvenation scheme is proposed for achieving the best attainable value of MTTF with respect to the parameters involved in the CTMC model.
Keywords: VoIP; software rejuvenation; continuous time Markov chain; system reliability; mean time to failure.
Effort-based software release and testing stop-time decisions
by Rana Majumdar, P.K. Kpaur, Sunil K. Khatri, A.K. Shrivastava
Abstract: To remain competitive and at the same time to satisfy the users' desire, these days software organisations are releasing the software early and removing the remaining number of bugs based on users' feedback or reports in the post-release testing phase. Early release may affect software performance owing to inadequate elimination of faults due to which the manufacturer may bear post-release cost of fixing the undetected faults. On the other hand, late release may increase the risk of more failures in the functioning environment. Software reliability can be achieved by efficient testing, and testing is directly proportional to testing effort/resources consumed. In this paper we have proposed a testing effort-based cost model to determine the optimal release and testing stop-time and corresponding optimal effort consumed by minimising the total cost. Numerical illustration is done to validate the proposed cost model.
Keywords: software reliability; release decisions; post-release testing; modelling; optimisation.
A Fuzzy based failure mode effect and criticality analysis of solar photovoltaic systems
by Sana Parveen, Haroon Ashfaq, Mohammad Asjad
Abstract: In this research work, a failure mode and effect analysis (FMEA) has been applied to a solar photovoltaic (SPV) system that consists of photovoltaic module, an inverter, connecting cable, battery and a charge controller. The FMEA is a tool that can gauge the possible failure mode(s) in order to determine the probability of the failure. The traditional (crisp) method of FMEA ranks all failure modes using risk priority number (RPN) according to severity order. However, traditional FMEA has been several disadvantages (like chance of error, human intelligence, etc.) which may be overcome by integrating them with an Artificial Techniques. Therefore, fuzzy logic is implemented to assess and ranks associated to each failure modes of different subassemblies of SPV system. Ranking of all failure modes has been done on the basis of fuzzy RPN, which is calculated by weighted Euclidean distance formula and centroid defuzzification method. It is expected that, this work will help the designers and practicing engineers by making them aware of the qualitative analysis of solar photovoltaic (SPV) systems.
Keywords: FMEA; SPV system; fuzzy RPN
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.