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The progressive regulatory moves in the competitive energy market have encouraged market participants to invest more in the green energy sector worldwide. The unpredictability of renewable energy s...

This research presents an in-class activity and accompanying homework assignment designed to encourage students to engage in critical thought about managerial decisions made by a real-world company...

This paper investigates a multiple-vacation M/M/1 warm-standby machine repair problem with an unreliable repairman. We first apply a matrix-analytic method to obtain the steady-state probabilities. Next, we construct the total expected profit per unit time and formulate an optimisation problem to find the maximum profit. The particle swarm optimisation (PSO) algorithm is implemented to determine the optimal number of warm standbys S* and the service rate μ* as well as vacation rate ν* simultaneously at the optimal maximum profit. We compare the searching results of the PSO algorithm with those of exhaustive search method to ensure the searching quality of the PSO algorithm. Sensitivity analysis with numerical illustrations is also provided.

This article analyses a repairable deteriorating system with quasi-renewal operating and repair times during warranty. To establish the importance of non-negligible repair times modelled with quasi-renewal processes in warranty cost analysis, a fixed warranty model is developed and the results are compared with an existing model using expected warranty cost. Sensitivity analysis and graphical illustrations are provided to highlight the effect of various cost parameters on the expected warranty cost by means of three different distributions. In order to examine the cost implications to the customer and manufacturer, an extended warranty model in which a manufacturer offers a warranty option to the customer with two different policies, has been proposed. Based on the long-run average cost per unit time, profit analysis has been carried out for the manufacturer as it is an essential aspect of warranty management. This article emphasises the incorporation of non-negligible ‘improved’ repair times during warranty.

This paper discussed a two-unit cold standby system by considering the concepts of degradation, inspection, preventive maintenance (PM), and priority. The unit works as a reduced capacity after its repair and is called degraded unit. There is a single repairman who visits the system immediately. The repairman inspects the failed degraded unit to see the feasibility of repair. If the repair of the degraded unit is not possible, it is replaced by new unit. PM will provide to the system when both the units are degraded and available for use. Priority for operation and repair is provided to new unit over-degraded unit. Various reliability characteristics such as mean time to system failure (MTSF), availability, busy period of the repairman, expected number of visits by the repairman, and profit of the system have been obtained using regenerative point graphical technique. For particular case, the results for MTSF, availability, and profit function are obtained considering exponential, Rayleigh, and Weibull distributions for all random variables.

This paper studies the machine-repair problem consisting of M operating machines with S spares, and R servers which themselves are subject to breakdown under steady-state conditions. Spares are considered to be either cold-standby, or warm-standby or hot-standby. Failure and service times of the machines, and breakdown and repair times of the servers, are assumed to follow a negative exponential distribution. Each server is subject to breakdown even if no failed machines are in the system. A profit model is developed in order to determine the optimal values of the number of servers and spares. Numerical results are provided in which several system characteristics are evaluated for all cases under the optimal operating conditions.

A model suitable for evaluating the performance of n-unit priority standby systems is developed. The modelling approach is fairly general and applies to most commonly used priority strategies including pre-emption. The results are employed to develop a profit analysis as a measure of system performance. An example system operating under a particular pre-emptive priority strategy is treated so as to demonstrate the modelling approach

This paper deals with the profit analysis of a single-server two-unit (one priority and the other ordinary) cold standby system subject to degradation. Initially the priority (P) unit is operative and the ordinary (O) unit is kept as the cold standby. It is assumed that the P-unit passes through three operative stages (excellent, good and satisfactory) before it fails. The P-unit enters into the total failure (F) mode only from the satisfactory stage, and after repair it enters into the normal (N) mode with any of the ‘excellent’, ‘good’ and ‘satisfactory’ stages with probabilities p1, p2 and p3 , respectively. Identifying the system at suitable regenerative instants, the integral equations are set up and the explicit expressions of interest to system designers are obtained to carry out the profit function analysis. The results are also derived in a particular case.

This paper studies the machine-repair problem with two different types of a single service station breakdown under steady-state conditions. In type 1, the service station can break down only when there is at least one failed machine in the system, while in type 2, the station can break down even if no failed machines are in the system. A profit model is developed in order to determine the optimal value of the number of machines to be assigned to the service station for both types. Numerical results are provided in which several system characteristics are evaluated under optimal operating conditions.

The profit analysis of a single server two-unit (one priority and the other ordinary) cold standby system with two modes normal and total failure is examined. The priority unit gets preference both for operation and repair. Whenever an operative unit fails, a delay occurs in locating the repairman and getting him to the system location due to certain administrative actions with known probability p. The system is observed at suitable regenerative epochs in order to obtain several economics-related reliability characteristics. Explicit results are obtained in a few particular cases.