Many maintenance optimization models need to iteratively evaluate the integrals with a renewal function being a part of the integrated function. For those cases, a simple and analytically tractable approximation to the renewal function is desired in order to facilitate the applications of the models. This paper proposes such an approximation that is applicable for both the Weibull and non-Weibull distributions. The approximation is obtained by neglecting the probability of having more than two failures, and hence is suitable for the situation where the evaluated time interval is not too large. This is often the case for maintenance optimization problems. The usefulness and appropriateness of the approximation is illustrated using examples.
Received on February 02, 2009, revised October 18, 2009
References: 23

The design of dynamic systems in terms of dependability and sustainability is a computationally intensive task - especially when probabilities are needed. This paper presents a methodology that greatly reduces the design time with a controlled loss of accuracy. The proposed approach combines design of computer experiments, a judicious application of linear metamodels and an explicit evaluation of probabilities. This approach is much faster than traditional Monte Carlo simulation. A further reduction in time can be accomplished through the application of singular value decomposition. The application of the methodology for two popular forms of metamodels (i.e. response surface methods via Least-squares fit and Kriging via maximum likelihood estimation) is presented. Parameter design is provided through robust design principles and constrained optimization. A detailed case study of a system with multiple performance measures and multiple design variables shows the efficacy and practicality of the methodology.
Received on March 11, 2009, revised on September 30, 2009
References: 19

This paper proposes an improved methodology for machine tool reliability analysis. The overall objective of the proposed methodology is to provide the machine tool manufacturers with the approach that will help them in making cost driven decisions while improving the performance of their machines in the field. The methodology consists of three parts viz., modified fault tree diagram, simulation based data analysis and cost based Failure Modes and Effects Analysis (FMEA). Modified fault tree diagram found useful in providing better insight into the failures and their impact. The simulation based approach helps in obtaining time to failure distribution parameters for each failure events using expert's judgements. The effect of uncertainty in the experts' judgements is also quantified in terms of 90 per cent confidence interval values of the parameters. Finally, the cost based FMEA proposed in this paper will help the manufacturer in identifying the critical failure events based on actual cost of failures to the users. The methodology is illustrated with the help of an example of a CNC grinding machine.
Received on March 15, 2009, revised October 21, 2009
References: 13

The purpose of this paper is to describe a methodology for the identification of different operational consequences and associated costs, caused by known or suspected technical difficulties or malfunctions caused by aircraft system failure, in order to facilitate and enhance the capability of taking correct and efficient decisions for design of required maintenance tasks, analysis of cost-effectiveness, and possible design modifications. To identify the operational consequences of the technical interruption of failures, empirical studies of possible scenarios involving aircraft failures and their operational consequences for a commercial airline have been performed. Empirical data were extracted through document studies and interviews, guided by the application of an Event Tree Analysis (ETA). The study was performed together with experienced practitioners from an aircraft manufacturer and commercial airlines, which contributed to a verification of the study's outcome.
Received on April 17, 2009, revised November 03, 2009
References: 11

Screening new industrial product ideas at the early stages of a new product development process is a critical activity. Although making a good new product choice is vital, managers have not applied systematic screening models because these models have not been customized to reflect the particular character of their company and industry. A customized systematic procedure is proposed to manage the task of selecting potential new products for an electronic component distributor at the early stages of a new product development (NPD) process. Screening criteria have been reviewed and optimized by project leaders and managers closest to the new product selection decision. The screening model has been used in a company to predict the success or failure of projects, and these predictions have been compared to the actual results from real projects. Thus, the study provides insights into the capability of the screening model and suggests further improvements to the screening process.
Received on May 23, 2009, revised on October 17, 2009
References: 53

The cold load pick up current during frequent energization of the distribution transformers produces high stress and hot spot temperature in their windings. This condition is responsible for elongation in the winding conductors due to creep. The winding conductors between spacers become loose due to elongation which in turn causes turn to turn fault in the winding. Thus, creep causes failure of the distribution transformers. The steady state creep rate is an important design parameter which specifies strain rate in the wire during steady state creep stage. This paper reports the steady state creep rate of the aluminum and the copper wires used in the windings of the 25 kVA distribution transformers.
Received on May 08, 2009, revised on August 26,2009
References: 23

In every day life, we encounter events which have very diverse causes, mechanisms of development and consequences. It is the concept of the events′ description that is often of importance in safety or risk studies. In pure technical terms, these events are related to the occurrence of failures, be it of equipment, a device, a system or an item. This paper considers the complex, sometimes problematic, area of the term "failure" and its related characteristics. A two fold objective is pursued in this paper to understand the complexity of this fundamental term. The primary objective is to provide an understanding of the key concepts and classifications. In fact this is related to the functions of an object and its description, classification of failures, the main characteristics of failure, possible causes of failure, failure mechanisms and the consequences of failures. Each of these issues can be subdivided and illustrations are used to differentiate between these subdivisions. For example, to distinguish failure occurrence, the meaning of design failures, manufacturing failures and ageing failure etc is explained. The secondary objective is related to information sources. To gain information about a failure, it may need to be found or transferred from a variety of sources, these sources have been identified and discussed. In conclusion, this paper aims to offer an appraisal in understanding failures and their implications.
Received on October 31, 2008, revised on June 9, 2009
References: 09

Demands on water resources for household, commercial, industrial, and agricultural purposes are increasing greatly, and growing urbanization exacerbates the situation. Responsible water use is an integral part of sustainable communities. The use of reclaimed water for industrial use represents a significant potential market for reclaimed water in the City of Regina. Saskatchewan, Canada. The concept of reusing the Regina Wastewater Treatment Plant (RWWTP) effluent for cooling water and process water in industries in Regina may be economically attractive and sustainable. Preliminary investigation showed that the RWWTP effluent quality is generally not much different than the City of Regina drinking water and local groundwater except for nitrogen, phosphorus and bacteria levels. The study also showed that by assuming no further treatment is required, the effluent reuse scheme could be competitive with the supply of water from the City system. A more detailed economic analysis is needed once the treatment plant is upgraded by the installation of a biological nutrient removal system and other treatment needs are assessed.
Received on November 07, 2007, revised on August 05, 2009
References: 08