Maintainability and Availability of a complex semi-up system

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V.K. Pathak
H.L. Manker

Abstract

The increasing complexity of present day equipment has brought into focus the important aspects of reliability, known as maintainability and availability. When any system fails, the ease with which it is brought back into operation reflects, in some measure, the maintainability character of the equipment. Similarly, if the system is capable of being repaired easily or if it has high maintainability factor, then the availability will also be high. In this paper we will touch upon various factors leading to the calculation of MTSF, Availability, Busy period of the repairman in repairing the failed units and expected profit of a system which is laid in semi-up state. A system is defined into a semi-up state wherein, some units of the equipment are in failed state yet the equipment is delivering its normal work but the system cannot be put in working condition for a longer period to avoid the complete failure. In other words, we can classify such systems into systems working with failures till the immediate repairing facility arrives. Such systems may be useful in remote areas where, arduous type of work is done on robust machines and repair facility arrives late. In recent years many papers on reliability have been written in order to predict, estimate or optimize the probability of survival, the mean life or more generally the life distribution of components or systems. Earlier, Murari et al [7] have done reliability analysis taking units in two different modes. Rander et-al [4] has evaluated the cost analysis of two dissimilar cold standby systems with preventive maintenance and replacement of standby units. In the past, Arora et-al [2] has done reliability analysis of two unit standby redundant system with constrained repair time. Gupta et-al [6] has worked on a cold standby system with arrival time of server and correlated failures and repairs. A pioneer work in this field was done by Gopalan [1] and Osaki [3] by performing analysis of warm standby system and parallel system with bivariate exponential life respectively. Earlier Pathak et al [8& 9] studied reliability parameters of a main unit with its supporting units and also compared the results with two different distributions. In all the papers authors have worked with only two kinds of states i.e. up state and down state. However, there are times and conditions wherein the states are neither up or completely down mode. We can refer such states in sleeping mode or more in reliability terms they can be stated in semi-up mode. In many papers, the working system is often assumed to be down when the main unit is not operating. In fact, it is not so. There is need to conceptualize systems in Industries that are complex in nature but they yield such results which are more suitable to industries in order to meet the ever increasing demands of society. In this paper an attempt has been made by authors by incorporating the concept of semi-up mode and tried to obtain the reliability parameters of working system using regenerative point technique.

Keywords: Regenerative Point, MTSF, Availability, Busy Period

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