International Journal of Reliability and Safety (7 papers in press)
Reliability assessment and performance analysis of DFIG-based wind turbines for wind energy conversion system
by Om Prakash Bharti, R.K. Saket, S.K. Nagar
Abstract: This paper presents the reliability assessment and performance analysis of doubly fed induction generator (DFIG)-based wind turbines (WT) for accurate DFIG-based WT modelling. This model calculates and describes the reliability of each unit and component of the WECs by using the Markov process. To analyse the DFIG-based WT during transient and steady-state operations, both the control and modelling of the system are illustrated in detail. The main contribution of this paper is the reliability assessment of the DFIG-based WT units in terms of failures as well as repair rate and performance analysis in normal as well as faulty conditions. For fault analysis of the WECs, a DFIG-based WT has been simulated in MATLAB Simulink for line to line, line to ground and double line to ground fault study.
Keywords: renewable energy; wind energy conversion systems; wind turbine; synchronous generator; permanent magnet synchronous generator; doubly fed induction generator.
Probabilistic evaluation and design aspects for reliability enhancement of induction motors
by Sanjay Kumar, Sachin Kumar, Om Prakash Bharti, Lokesh Varshney, K.S. Anand Kumar, R.K. Saket, D.N. Vishwakarma
Abstract: This paper presents the probabilistic evaluation, design aspects and scientific suggestions to improve the reliability and performance of an industrial induction motor. The induction motors have experienced a long life and a high efficiency in service with appropriate design and quality control. However, reliability quantification and adequacy evaluation are still necessary and important for customer satisfaction, design improvement, marketing, vendor selection, production plan, service life determination and scheduled maintenance. The industrial data related to manufacturing and failure of induction motors are analysed for reliability assessment and design suggestions. The reliability indices, such asMTBF and failure rate of induction motors, are evaluated using industrial data based exponential distribution function, which is issued to plan the maintenance schedule of the industrial induction motors. The technological suggestions are finally presented in this paper to reduce the failure rate and enhance the MTBF for reliability improvement of induction motors.
Keywords: probabilistic evaluation; design aspect; induction motor; reliability improvement; MTBF; MTTF; failure rate; exponential distribution function.
Bearing health assessment based on Hilbert transform envelope analysis and cluster analysis
by Xin Zhang, Jianmin Zhao, Xianglong Ni, Haiping Li, Fucheng Sun
Abstract: The rolling bearings are one of the most critical and prevalent elements in rotating machinery. It is necessary to develop a suitable health assessment method to prevent malfunctions and breakages during operation. In this paper, a novel health assessment method for bearings based on Hilbert transform envelope analysis and cluster analysis is proposed. 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. And the combination of time domain features parameters is chosen to evaluate the bearing health state. Then extracted feature parameters are clustered by using improved K-means algorithm. In this paper, bearing degradation data and fault data are used to prove the effectiveness of the method.
Keywords: cluster analysis; bearing; Hilbert transform; envelope analysis; high-pass filter; health assessment; feature parameter; K-means algorithm; degradation; rotating machinery.
An optimal rejuvenation scheme for improving VoIP service reliability in the existence of resource exhaustion and security breaches
by Vandana Gupta, Rahul Kumar
Abstract: The escalating number of end-users of VoIP and the challenges faced in furnishing first-class quality of service (QoS) are the major driving forces for research in the area of VoIP. When the resources allotted to every end-user get exhausted, it leads to a decline in the QoS. Further, as VoIP is an application operating on the internet, it is prone to security breaches. This paper addresses the issues of resource exhaustion and security breaches in a VoIP network. To help avert performance degradation in a VoIP system, software rejuvenation is also 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. Furthermore, an optimal rejuvenation scheme is proposed for achieving the best attainable value of MTTF.
Keywords: VoIP; software rejuvenation; CTMC; continuous time Markov chain; system reliability; MTTF; mean time to failure.
Effort-based software release and testing stop time decisions
by Rana Majumdar, P.K. Kapur, 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 report in the post-release testing phase. Early release may affect software performance due 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 propose 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; cost modelling; optimisation.
A fuzzy-based failure mode effect and criticality analysis of solar photovoltaic systems
by Sana Perveen, 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 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 several disadvantages (like chance of error, human intelligence, etc.) which may be overcome by integrating them with artificial intelligence techniques. Therefore, fuzzy logic is implemented to assess and ranks associated with each failure mode 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 engineers by making them aware of the qualitative analysis of SPV systems.
Keywords: FMEA; failure mode and effect analysis; SPV system; fuzzy RPN.
A TSST of the reliability function for exponential failure model using type II censored data with minimum cost of experimentations
by Zuhair A. Al-Hemyari, Alla K. Jiheel
Abstract: This paper considers a class of an efficient 'two-stage shrinkage testimator' (TSST) of 'reliability function' of 'exponential distribution', and the class uses additional information which can be obtained from the past practices, and in the form of past initial estimates (λ0) about the unknown parameter λ. The TSST is dependent upon a convenient shrinking factor, conventional estimators, the 'right censored plan' of sj 'ordered observations' of a variable sample of 'size' Sj and by developing five 'testing regions' for screening the 'closeness' of λ0 to λ by different 'criteria'. The computations of 'bias', 'mean squared error', 'expected sample size' and 'relative efficiency' 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 paper an application to a 'life time' problem is provided to illustrate 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 and 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; efficiency.