Browsing by Author "Mendez, Carlos A."
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- A hybrid scheduling approach for automated flowshops with material handling and time constraintsPublication . Aguirre, Adrian M.; Mendez, Carlos A.; Castro, PedroFlowshop scheduling problems have been extensively studied by several authors using different approaches. A typical flowshop process consists of successive manufacturing stages arranged in a single production line where different jobs have to be processed following a predefined production recipe. In this work, the scheduling of a complex flowshop process involving automated wet-etch station from semiconductor manufacturing systems requires a proper synchronisation of processing and transport operations, due to stringent storage policies and fixed transfer times between stages. Robust hybrid solution strategies based on mixed integer linear programming formulations and heuristic-based approaches, such as aggregation and decomposition methods, are proposed and illustrated on industrial-scale problems. The results show significant improvements in solution quality coupled with a reduced computational effort compared to other existing methodologies.
- Multi-period design and planning of closed-loop supply chains withuncertain supply and demandPublication . Zeballos, Luís J.; Mendez, Carlos A.; Barbosa-Póvoa, Ana Paula; Novais, Augusto Q.A design and planning approach is proposed for addressing general multi-period, multi-product closed-loop supply chains (CLSCs), structured as a 10-layer network (5 forward plus 5 reverse flows), with uncertain levels in the amount of raw material supplies and customer demands. The consideration ofa multi-period setting leads to a multi-stage stochastic programming problem, which is handled by amixed-integer linear programming (MILP) formulation. The effects of uncertain demand and supply onthe network are considered by means of multiple scenarios, whose occurrence probabilities are assumed to be known. Several realistic supply chain requirements are taken into account, such as those relatedto the operational and environmental costs of different transportation modes, as well as capacity limitson production, distribution and storage. Moreover, multiple products are considered, which are groupedaccording to their recovery grade. The objective function minimizes the expected cost (that includes facil-ities, purchasing, storage, transport and emissions costs) minus the expected revenue due to the amount of products returned, from repairing and decomposition centers to the forward network. Finally, com-putational results are discussed and analyzed in order to demonstrate the effectiveness of the proposedapproach. Due to the large size of the addressed optimization problem containing all possible scenariosfor the two uncertain parameters, scenario reduction algorithms are applied to generate a representative,albeit smaller, subset of scenarios.
- Scope for industrial applications of production scheduling models and solution methodsPublication . Harjunkoski, Iiro; Maravelias, Christos T.; Bongers, Peter; Castro, Pedro; Engell, Sebastian; Grossmann, Ignacio E.; Hooker, John; Mendez, Carlos A.; Sand, Guido; Wassick, JohnThis paper gives a review on existing scheduling methodologies developed for process industries. Above all, the aim of the paper is to focus on the industrial aspects of scheduling and discuss the main characteristics, including strengths and weaknesses of the presented approaches. It is claimed that optimization tools of today can effectively support the plant level production. However there is still clear potential for improvements, especially in transferring academic results into industry. For instance, usability, interfacing and integration are some aspects discussed in the paper. After the introduction and problem classification, the paper discusses some lessons learned from industry, provides an overview of models and methods and concludes with general guidelines and examples on the modeling and solution of industrial problems.