A review of multi-component maintenance models with economic dependence

In this paper we review the literature on multi-component maintenance models with economic dependence. The emphasis is on papers that appeared after 1991, but there is an overlap with Section 2 of the most recent review paper by Cho and Parlar (1991). We distinguish between stationary models, where a long-term stable situation is assumed, and dynamic models, which can take information into account that becomes available only on the short term. Within the stationary models we choose a classification scheme that is primarily based on the various options of grouping maintenance activities: grouping either corrective or preventive maintenance, or combining preventive-maintenance actions with corrective actions. As such, this classification links up with the possibilities for grouped maintenance activities that exist in practice

Irrigation scheduling of grapefruit trees in a mediterranean environment throughout evaluation of plant water status and evapotranspiration

In this study, 1 full irrigation regime (100% of crop evapotranspiration, I100) and 2 deficit irrigation regimes (70%, I70, and 50%, I50) were evaluated in a Rio Red grapefruit (Citrus paradisi Macfad. ‘Rio Red’) orchard in Adana, Turkey. Fruit yield, leaf water potential (LWP), and soil water depletion (SWD) were measured among trees from each treatment. Actual evapotranspiration was calculated in 3 ways, using 2 energy balance methods (eddy correlation and Bowen’s ratio) and water balance. Evapotranspiration rates of I70 and I50 treatments were 10% and 18% less than I100, respectively. Average irrigation amount for I50 was less than half of the average irrigation amount for I100. Considering that yield for the experimental treatments did not change statistically significantly, the I50 treatment provided about 50% more irrigation water savings than full irrigation conditions. Grapefruit tree LWP was highly correlated to soil water status and significantly associated with irrigation treatment. Average LWP values for treatments were -2.70 MPa for I100, -2.96 MPa for I70, and -3.28 MPa for I50. LWP increased up to a threshold level equivalent to 60%-66% of SWD, above which LWP decreased linearly with a continuous increase of SWD. This indicates that an average LWP of -3.28 MPa can be allowed for grapefruit under these experimental conditions while keeping the crop yield at that of full irrigation levels. The research findings showed that an enhanced understanding of physiological parameters is essential for irrigation scheduling of fruit plants. These will result in obtaining the optimum yield of fruit while conserving water. © TÜBİTAK

A disruption recovery model in a production-inventory system with demand uncertainty and process reliability

This paper develops a risk management tool for a productioninventory system that involves an imperfect production process and faces production disruption and demand uncertainty. In this paper, the demand uncertainty is represented as fuzzy variable and the imperfectness is expressed as process reliability. To deal with the production scheduling in this environment, a non-linear constrained optimization model has been formulated with an objective of maximizing the graded mean integration value (GMIV) of the total expected profit. The model is applied to solve the production-inventory problem with single as well as multiple disruptions on a real time basis that basically revises the production quantity in each cycle in the recovery time window. We propose a genetic algorithm (GA) based heuristic to solve the model and obtain an optimal recovery plan. A numerical example is presented to explain usefulness of the developed model. © 2013 IFIP International Federation for Information Processing