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Volume 11, Number 3, May 2015 - Editorial - p 201



We have nine papers included in this issue. They come from different areas of applications for variety of systems and use new modelling approaches.

The first paper, A System Dynamics Model for Transient Availability Modeling of Repairable Redundant Systems, combines the Markov approach with system dynamics simulation approach for availability modelling of a system. Further the paper demonstrates that the authors’ approach can be used for transient availability modeling both with time varying failure and repair rates as well as constant failure and repair rates.

In the second paper of this issue, A Comparison of Hidden Markov and Semi-Markov Modeling for a Deterioration System subject to Vibration Monitoring, the authors compare a hidden Markov and Erlang semi-Markov modeling of a partially observable deteriorating system operating under a varying load and subject to multi-sensor vibration monitoring. The evolution of the unknown state process is described by a hidden, two state semi-Markov process with an Erlang sojourn time distribution in the healthy state. The unknown model parameters are estimated using the EM algorithm. The authors derive explicit formulae for the parameter re-estimation in the EM algorithm, which provides a fast estimation procedure.

The third paper of the issue, An Integrated Approach for Fleet Level Maintenance Planning, the authors develop an integrated approach to simultaneously optimize the decision of location of maintenance, the level of indenture for maintenance, the degree of maintenance and the level of repair spares inventory at different echelons. The authors use time dependent failure rate model for different part failure in a machine. This helps in considering preventive maintenance (PM) for machine and to integrate PM plans with above decisions.

In the fourth paper, Reliability Estimation Based on Moving Average and State Space Model for Rolling Element Bearing, a new method for rotating machine reliability estimation is presented. Wavelet packet feature extraction, moving average, and SSM are combined together for condition estimation. Based on the rolling element bearing analysis, the effectiveness of this method is demonstrated. The results indicate that the moving average filtering can effectively improve the signal noise ratio of the degradation characteristics and improve the accuracy of the prediction.

The fifth paper, Experimental Studies of In-House Developed Magnetorheological Fluid in a Damper, presents a process to develop stable MR fluid using in-house technology at a fraction of cost at which the fluid is available commercially. The developed fluid is tested for on-state as well as off-state rheological properties in a fabricated prototype MR damper.

In the sixth paper, Bi-Objective Topology Design of Communication Networks Using Dynamic Programming, the authors present, what they call as called NTD-CR/B, to design networks with minimum cost and maximum reliability subject to the condition of satisfying a required operational bandwidth. For a given a set of nodes, their possible connecting links, link failure rate, bandwidth and installation cost, the problem selects the best set of links such that the resulting topology meets its required bandwidth Bmin while minimizing its installation cost and maximizing its reliability.

The seventh paper of this issue, Examining Efficacy of Metamodels in predicting Ground Water Table,

the authors examine the capability of Gaussian Process Regression (GPR), Generalized Regression Neural Network (GRNN) and Relevance Vector Machine (RVM) for prediction of Ground Water Table (dw) at a site. RVM, GRNN and GPR have been adopted as regression techniques. The results show that the developed RVM gives the best model for prediction of dw at the site, viz., at Vellore.

In the eighth paper, Hybrid Tool for Optimal Preventive Maintenance Schedule for Deteriorating Systems, the authors claim that a hybrid tool combining Simulated Annealing and integrating it with graphical model provides a feasible alternative in arriving at decisions regarding the feasibility of preventive maintenance (PM) over break down maintenance (BDM) and hence providing close to global optimal schedules for PM of deteriorating systems while maximizing availability.

In the last paper of the issue, Stochastic Analysis of a Two-Unit Cold Standby System with Arbitrary Distributions for Life, Repair and Waiting Times, the authors discuss a stochastic model considering general distributions for life, repair and waiting times. Expressions for various measures of the system effectiveness have been derived by making use of semi-Markov processes and regenerative point technique.

Besides the above nine papers, reviews of four latest books are provided in this issue for the benefit of IJPE readers.

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