A systematic airport runway maintenance and inspection policy based on a delay time modeling approach

Operations research applications of dichotomous search

As businesses operating in the production sector often need to deal with defective products and machine breakdowns, they may experience challenges in their production planning and control processes. This study addresses random machine breakdown to derive an optimal production time for defective products under an abort/resume inventory control policy. Machine time-to-breakdown involves two scenarios: namely, the occurrence of machine breakdown during production and its occurrence after production. Total expected cost functions are derived for each scenario. The average cost is then assessed in terms of expense over time. This study explores assumptions such as the performance of the inspection both during and after production, defective products being discarded, and others being sold at discount prices, and the time-to-breakdown being exponentially distributed. Numerical examples are given to explain the model which has been developed, and the convex formation of the expected function of total cost is illustrated in a graph. Optimal values are investigated for production time and total cost based on two different values of the number of machine breakdowns per unit time. Sensitivity analyses are used to show how a number of system parameters affect the optimal solution. These analyses demonstrate that the demand rate and the number of machine breakdowns have a significant effect on the optimal solutions.

Modeling an inventory problem with random supply, inspection and machine breakdown

An economic off-line inspection/disposition approach is proposed, which incorporates manufacturing variation. This approach includes a new inspection algorithm for inspections based on cost minimization and utilizing a specified confidence level for identifying in-control items. This approach addresses two situations not addressed in previous papers: (i) the last unit in the batch is conforming; (ii) inspection time is non-negligible. Advantages are that there is no need to record the original position of each unit, the impact of manufacturing variation is reduced and non-negligible inspection times can be easily incorporated. Comparisons of this approach to other approaches are provided.

An economic off-line quality control approach for unstable production processes

Supply chains are vulnerable to disruptions at any stage of the distribution system. These disruptions can be caused by natural disasters, production problems, or labor defects. The consequences of these disruptions may result in significant economic losses or even human deaths. Therefore, it is important to consider any disruption as an important factor in strategic supply chain design. Consequently, the primary outputs of this dissertation include insights for designing robust supply chains that are neither significantly nor adversely impacted by disruptions. The impact of correlated supplier failures is examined and how this problem can be modeled as a variant of a facility location problem is described. Two main problems are defined, the first being the design of a robust supply chain, and the second being the optimization of operational inspection schedules to maintain the quality of an already established supply chain. In this regard, both strategic and operational decisions are considered in the model and (1) a twostage stochastic programming model; (2) a multi-objective stochastic programming model; and (3) a dynamic programming model are developed to explore the tradeoffs between cost and risk. Three methods are developed to identify optimal and robust solutions: an integer L-shaped method; a hybrid genetic algorithm using Data Envelopment Analysis; and an approximate dynamic programming method. Several sensitivity analyses are performed on the model to see how the model output would be affected by uncertainty. The findings from this dissertation will be able to help both practitioners designing supply chains, as well as policy makers who need to understand the impact of different disruption mitigation strategies on cost and risk in the supply chain.

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Designing a robust supply chain network against disruptions

This study presents an off-line inspection problem for a batch produced from a process subject to random failures and exhibiting manufacturing variations. The objective of this paper is to develop an inspection policy in which units should be inspected in a particular order to find the transition unit in the batch under a required confidence level. This study develops an algorithm to compute the expected number of inspections. This approach uses the information theory of entropy to select an un-inspected unit to be inspected, and effectively minimizes the uncertainty of the transition unit in the production batch. A numerical example illustrates the proposed off-line inspection policy, and the effects of model parameters on the expected inspection number are investigated. The numerical example in this study indicates that full inspection is required when the required confidence level is one or the process has larger manufacturing variations.

Utilizing the information theory of entropy to solve an off-line inspection problem

Economic production lot size models with a process inspection delay have been studied over several decades in the literature. When an imperfect process is assumed to have a given probability to run from an in-control state to an out-of-control state each time an item is produced, an inspection schedule is arranged to monitor the process reliability; however, a time delay to obtain the inspection results exists. This study further includes process restoration cost in the inspection/production model to study its effects on the optimal production lot size and the economic inspection lot under the consideration of minimizing the approximated total cost per week. For the case of multiple inspections, when the restoration cost is considered, the resulting the economic inspection lot may depend on the production lot size, especially when the fixed part of the restoration cost is large.

W. C. Tsai

Papers

Utilizing the information theory of entropy to solve an off-line inspection problem

The effects of inspection delay and restoration cost on the optimal inspection and production policy