International Journal of Reliability and Safety (5 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 a photovoltaic module, an inverter, connecting cable, battery and 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 (such as chance of error, human intelligence, etc.) which may be overcome by integrating them with an artificial technique. Therefore, fuzzy logic is implemented to assess and rank each failure mode of different subassemblies of an 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 practising engineers by making them aware of the qualitative analysis of SPV systems.
Keywords: FMEA; SPV system; fuzzy RPN.
A TSST of the reliability function for exponential failure model using Type II censored data with minimum cost of experimentation
by Zuhair Al-Hemyari, Alla Jiheel
Abstract: This article considers a class of efficient two-stage shrinkage testimator (TSST) of the reliability function of an exponential distribution, and the class uses additional information that can be obtained from the past estimation practices, and in the form of past initial estimate about the unknown parameter. The TSST is dependent on a convenient shrinking factor, conventional estimators, the right censored plan of ordered observations of a valiable sample of size and by developing five testing regions for screening the closeness by different criteria. A conceptually transparent derivation of the measures bias, mean squared error, expected sample size and relative efficiency are discussed. In order to study the behaviour and the properties of the proposed estimator, different criteria have been employed. Comprehensive empirical computations of the criteria bias, mean squared error, expected sample size and relative efficiency, probability of avoiding the second stage sample, and the percentage of overall sample saved of TSST are carried out. The computations show that the behaviour of the class of TSST is almost similar to existing testimators and better than classical and similar estimators in several properties, for different constants and variables involved in it. Throughout the article an application in a lifetime problem is provided to illustrate the applicability of the TSST and expressions that are obtained from it. The behaviour of the developed TSST and the significant comparative results offer some useful sufficient insights for researchers to continue in the TSST direction, and give adequate reasons for experimenters/practitioners to use TSST in their applications.
Keywords: reliability function; Bessel’s function; exponential failure model; two-stage shrinkage; minimum experimentation; type II censored data; relative efficiency.