Scheduling a Dynamic Aircraft Repair Shop with Limited Repair Resources

We address a dynamic repair shop scheduling problem in the context of military aircraft fleet management where the goal is to maintain a full complement of aircraft over the long-term. A number of flights, each with a requirement for a specific number and type of aircraft, are already scheduled over a long horizon. We need to assign aircraft to flights and schedule repair activities while considering the flights requirements, repair capacity, and aircraft failures. The number of aircraft awaiting repair dynamically changes over time due to failures and it is therefore necessary to rebuild the repair schedule online. To solve the problem, we view the dynamic repair shop as successive static repair scheduling sub-problems over shorter time periods. We propose a complete approach based on the logic-based Benders decomposition to solve the static sub-problems, and design different rescheduling policies to schedule the dynamic repair shop. Computational experiments demonstrate that the Benders model is able to find and prove optimal solutions on average four times faster than a mixed integer programming model. The rescheduling approach having both aspects of scheduling over a longer horizon and quickly adjusting the schedule increases aircraft available in the long term by 10% compared to the approaches having either one of the aspects alone.

The Application of the Minimum Cut Sets in Reliability Evaluation of Power Transmission and Transformation System

As an important part of power systems, power transmission and transformation system involves various equipments, complicated structure and operation modes, and its reliability level has a significant influence on the reliability of the whole system. The paper proposes a practical method for reliability evaluation of power transmission and transformation system based on minimum cut sets. The algorithm, based on topological structure and reliability data without power flow, analyses the reliability of system by different voltage grades. In each voltage grade analysis, the method resolves minimum path sets by depth first search method, gets minimum cut sets, and calculates reliability index. The method considers three states involved normal operating, schedule repair and fault repair, and it makes the evaluation process much more reasonable and effective as it resolves branch-node mixed cut sets. The paper verifies the effectiveness of the algorithm by the test of IEEE-RTS 79 system

Applying the TOC Thinking Process: A case study in the government sector

In the past, the TOC Thinking Process (TP) has been primarily applied to address managerial challenges in private sector manufacturing, logistics, and project-oriented organizations. The purpose of this paper is to present an application of the TOC TP in a public sector service organization, namely, the Water Utility Division Maintenance System (WUDMS) within the Albuquerque Public Works Department. The two necessary conditions for meeting the WUDMS's goal of effective management are (1) completing work in a waste-free manner and (2) responding promptly to customer requests for service. Although seven undesirable effects (UDEs) were identified by the improvement team, UDEs from three diverse areas were selected for creating the requisite conflict clouds, namely, (1) much repair work is not completed promptly, (2) WUDMS has some wasteful practices, and (3) managers are unable to schedule repair work effectively. Entities from these conflict clouds were synthesized into a core conflict cloud that revolved around the issue of dedicating more human resources to repair work or improvement efforts and that formed the base of the Current Reality Tree. By surfacing assumptions underlying entity pair relationships within the core conflict, a strategic direction for change was identified as: expansion of WUDMS capacity through the use of non-traditional resources. This injection was logically validated via a Future Reality Tree. Initial results from its implementation demonstrate that the direction of the solution is correct.