574 research outputs found
Multi-product economic lot scheduling problem with separate production lines for manufacturing and remanufacturing
Get PDFWe study the economic lot scheduling problem with two production sources, manufacturing and remanufacturing, for which operations are performed on separate, dedicated lines. We develop an exact algorithm for finding the optimal common-cycle-time policy. The algorithm combines a search for the optimal cycle time with a mixed integer programming (MIP) formulation of the problem given a fixed cycle time. Using case study data from an auto part producer, we perform a sensitivity study on the effects of key problem parameters such as demand rates and return fractions. Furthermore, by comparing to results in Tang and Teunter [Tang, O., Teunter, R.H., 2006. Economic lot scheduling problem with returns. Production and Operations Management] for the situation where all operations are performed on the same line, we analyze the cost benefits of using dedicated lines
Heuristics for the economic lot scheduling problem with returns. [In special section on problems and models of inventories selected papers of the fourteenth International symposium on inventories]
Get PDFWe study the multi-item economic lot scheduling problem (ELSP) with two sources of production: manufacturing of new items and remanufacturing of returned items. Manufacturing and remanufacturing operations are performed on the same production line. Tang and Teunter [2006. Economic lot scheduling problem with returns. Production and Operations Management 15 (4), 488–497.] recently presented a complex algorithm for this problem that determines the optimal solution within the class of policies with a common cycle time and a single (re)manufacturing lot for each item in each cycle. This algorithm is rather complex and time consuming, combining a large MIP formulation with a search procedure, and may therefore not always be practical. In this paper, we deal with this type of problems and propose simple heuristics that are very fast and can be applied in a spreadsheet package. A large numerical study shows that the heuristics provide close to optimal solutions
The Repair Kit Problem with positive replenishment lead times and fixed ordering costs
Get PDFThe Repair Kit Problem (RKP) concerns the determination of a set of items taken by a service engineer to perform on-site product support. Such a set is called a kit. Models developed in the literature have always ignored the lead times associated with delivering items to replenish the kit, thereby limiting the practical relevance of the proposed solutions. Motivated by a real life case, we develop a model with positive lead times to control the replenishment quantities of the items in the kit, and study the performance of ( s , S ) policies under a service objective. The choice for ( s , S ) policies is made in order to accommodate fixed ordering costs. We present a method to calculate job fill rates with exact expressions, and discuss a heuristic approach to optimize the reorder level and order-up-to level for each item in the kit. The empirical utility of the model is assessed on real world data from an equipment manufacturer and useful insights are offered to after-sales managers
Multi-product economic lot scheduling problem with separate production lines for manufacturing and remanufacturing
No full textWe study the economic lot scheduling problem with two production sources, manufacturing and remanufacturing, for which operations are performed on separate, dedicated lines. We develop an exact algorithm for finding the optimal common-cycle-time policy. The algorithm combines a search for the optimal cycle time with a mixed integer programming (MIP) formulation of the problem given a fixed cycle time. Using case study data from an auto part producer, we perform a sensitivity study on the effects of key problem parameters such as demand rates and return fractions. Furthermore, by comparing to results in Tang and Teunter [Tang, O., Teunter, R.H., 2006. Economic lot scheduling problem with returns. Production and Operations Management] for the situation where all operations are performed on the same line, we analyze the cost benefits of using dedicated lines.
Heuristics for the economic lot scheduling problem with returns
No full textWe study the multi-item economic lot scheduling problem (ELSP) with two sources of production: manufacturing of new items and remanufacturing of returned items. Manufacturing and remanufacturing operations are performed on the same production line. Tang and Teunter [2006. Economic lot scheduling problem with returns. Production and Operations Management 15 (4), 488-497.] recently presented a complex algorithm for this problem that determines the optimal solution within the class of policies with a common cycle time and a single (re)manufacturing lot for each item in each cycle. This algorithm is rather complex and time consuming, combining a large MIP formulation with a search procedure, and may therefore not always be practical. In this paper, we deal with this type of problems and propose simple heuristics that are very fast and can be applied in a spreadsheet package. A large numerical study shows that the heuristics provide close to optimal solutions.ELSP Returns Remanufacturing Reverse logistics
Classification for forecasting and inventory
No full textABC classifications are commonly used to streamline a large number of SKUs into fewer, more manageable categories. As Aris, John, and Ruud explain, this classification may be useful for inventory control, but it does not provide much help in the selection of appropriate forecasting methods. The authors demonstrate a need for a classification that accounts for demand patterns and customer characteristics. Copyright International Institute of Forecasters, 201
Enhanced lateral transshipments in a multi-location inventory system
Get PDFIn managing an inventory network, two approaches to the pooling of stock have been proposed. Reactive transshipments respond to shortages at a location by moving inventory from elsewhere within the network, while proactive stock redistribution seeks to minimize the chance of future stockouts. This paper is the first to propose an enhanced reactive approach in which individual transshipments are viewed as an opportunity for proactive stock redistribution. We adopt a quasi-myopic approach to the development of a strongly performing enhanced reactive transshipment policy. In comparison to a purely reactive approach to transshipment, service levels are improved while a reduction in safety stock levels is achieved. The aggregate costs incurred in managing the system are significantly reduced, especially so for large networks. Moreover, an optimal policy is determined for small networks and it is shown that the enhanced reactive policy substantially closes the gap to optimality
Optimality, flexibility and efficiency for cell formation in group technology
Get PDFHet onderzoek van Dmitry Krushynskyi concentreert zich op de ontwikkeling van mathematische modellen voor celformatie (CF), die in de praktijk kunnen worden gebruikt om bedrijfsprestaties te verbeteren. Hoewel al meer dan 50 jaar onderzoek is gedaan naar het CF-probleem, baseren de meeste methoden zich op intuïtieve overwegingen en kampen ze onder meer met modellerings- en rekenfouten. Een ander nadeel van de meeste bestaande modellen is hun gebrek aan flexibiliteit: als een model op een ad hoc-procedure is gebaseerd, veroorzaakt elke nieuwe beperking een belangrijke wijziging van het model. In het proefschrift worden twee modellen ontwikkeld.
The thesis focuses on a development of optimal, flexible and efficient models for cell formation (CF) in group technology. By optimality is meant guaranteed quality of the solutions provided by the model, by flexibility - possibility of taking additional constraints and objectives into account, by efficiency - reasonable running times. The main aim is, thus, to provide a reliable tool that can be used by managers to design manufacturing cells based on their own preferences and constraints imposed by a particular manufacturing system.
Though the CF problem has been extensively studied for more than 50 years, there have been very few attempts of solving the problem to optimality and almost all the proposed models for CF problem are either of intuitive (heuristic) nature or are solved by heuristic procedures. This means that the obtained solutions incorporate two types of errors: an intrinsic error of modelling and a computational error induced by a heuristic solution procedure.
The author proposes two models based on the p-Median and the minimum multicut problems, respectively. The first model has very short running times (usually less than 1 sec.) at a cost of a small modelling error. The second approach excludes the modelling error but has substantially larger (yet, practically acceptable) running times. Both models are expressed in terms of Mixed Integer Linear Programs and require a general-purpose MILP solver, like CPLEX or Xpress. Several realistic constraints and objectives, as well as the ways of introducing them into the proposed modes, are discussed.
Condition-based maintenance for complex systems: coordinating maintenance and logistics planning for the process industries
Get PDFMaintenance planning in the process industries is extremely complex for various reasons. Plants often run nonstop, allowing little time for performing preventive maintenance. Failures should be prevented, however, as they can lead to system downtime and high losses of revenue. Corrective maintenance strategies are thus not suitable. Moreover, preventive maintenance strategies, such as time- or age-based maintenance, are generally too conservative, by scheduling maintenance more often than strictly necessary. Condition-Based Maintenance (CBM) therefore offers a lot of potential, as it bases the maintenance decisions on the actual system condition. Besides, in the process industries, systems generally comprise multiple components subject to various inter-component dependencies. In such cases, the optimal policy for one component may not result in a close-to-optimal solution at the system level. In this thesis, we focus on obtaining insights into the optimal CBM policy structure for systems subject to various types of dependencies, thereby focusing on decisions such as when to inspect, when to maintain, when to add a redundant component, and when to order spares. Our key finding is that CBM planning extends beyond merely using monitoring information to schedule maintenance right before component failure. Component dependencies can severely complicate the (maintenance) decisions at the system level. Many complex systems require a custom-fit, dynamic CBM policy, as classical maintenance policies or threshold CBM policies can be significantly more expensive. The insights obtained in this thesis constitute an important step towards such customized CBM policies
Forty years of the European Journal of Operational Research: A bibliometric overview
Get PDFThe European Journal of Operational Research (EJOR) published its first issue in 1977. This paper presents a general overview of the journal over its lifetime by using bibliometric indicators. We discuss its performance compared to other journals in the field and identify key contributing countries/institutions/authors as well as trends in research topics based on the Web of Science Core Collection database. The results indicate that EJOR is one of the leading journals in the area of operational research (OR) and management science (MS), with a wide range of authors from institutions and countries from all over the world publishing in it. Graphical visualization of similarities (VOS) provides further insights into how EJOR links to other journals and how it links researchers across the globe. (C) 2017 Elsevier B.V. All rights reserved.Complex Engineering Systems Institute / ISCI, ICM-FIC: P-05-004-F, CONICYT: FB0816 /
Fondecyt Regular Program, 116028
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