2011
Autores
Amorim, P; Antunes, CH; Almada Lobo, B;
Publicação
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
Abstract
The recent evidence demonstrating the importance of perishables in terms of store choice and shopping experience makes these products a very interesting topic in many different research areas. Nevertheless, the production planning research has not been paying the necessary attention to the complexities of production systems of such items. The evidence that consumers of perishable goods search for visual and other cues of freshness, such as the printed expiry dates, triggered the development of a multi-objective lot-sizing and scheduling model taking this relevant aspect into account by considering it explicitly as an objective function. A hybrid genetic algorithm based on NSGA-II was developed to allow the decision maker a true choice between different trade-offs from the Pareto front. Computational experiments were based on a case study, reported in the literature, concerning a diary company producing yogurt.
2011
Autores
James, RJW; Almada Lobo, B;
Publicação
COMPUTERS & OPERATIONS RESEARCH
Abstract
We propose a general-purpose heuristic approach combining metaheuristics and mixed integer programming to find high quality solutions to the challenging single- and parallel-machine capacitated lotsizing and scheduling problem with sequence-dependent setup times and costs. Commercial solvers fail to solve even medium-sized instances of this NP-hard problem; therefore, heuristics are required to find competitive solutions. We develop construction, improvement and search heuristics all based on MIP formulations. We then compare the performance of these heuristics with those of two metaheuristics and other MIP-based heuristics that have been proposed in the literature, and to a state-of-the-art commercial solver. A comprehensive set of computational experiments shows the effectiveness and efficiency of the main approach, a stochastic MIP-based local search heuristic, in solving medium to large size problems. Our solution procedures are quite flexible and may easily be adapted to cope with model extensions or to address different optimization problems that arise in practice.
2011
Autores
Menezes, AA; Clark, A; Almada Lobo, B;
Publicação
JOURNAL OF SCHEDULING
Abstract
In production planning, sequence dependent setup times and costs are often incurred for switchovers from one product to another. When setup times and costs do not respect the triangular inequality, a situation may occur where the optimal solution includes more than one batch of the same product in a single period-in other words, at least one sub tour exists in the production sequence of that period. By allowing setup crossovers, flexibility is increased and better solutions can be found. In tight capacity conditions, or whenever setup times are significant, setup crossovers are needed to assure feasibility. We present the first linear mixed-integer programming extension for the capacitated lot-sizing and scheduling problem incorporating all the necessary features of sequence sub tours and setup crossovers. This formulation is more efficient than other well known lot-sizing and scheduling models.
2011
Autores
Gomes, C; Sperandio, F; Borges, J; Almada Lobo, B; Brito, A;
Publicação
ENTERPRISE INFORMATION SYSTEMS, PT 3
Abstract
From lone to short term planning, the decision processes inherent to surgery theatre organization are often subject of empiricism. The current hospital information systems available on Portuguese public hospitals lack a decision support system component that could help achieve better planning solutions, thus better operational performance of the surgery theatre. Since the surgery theatre is the biggest hospital budget consumer, the use of surgery related resources and its intrinsic planning must be carefully studied. We developed a new decision support system for surgery planning conjointly with one of the largest hospitals in the north of Portugal. As for now, the goals of the DSS are to improve the planning process and increase policy compliance. We will enhance this framework by integrating data mining, optimization and simulation techniques in a way that enables a more accurate representation of the surgery theatre problems' stochastic nature, allowing the users to rind enhanced planning alternatives.
2011
Autores
Ferreira, I; Cabral, JA; Saraiva, P;
Publicação
Injection Molding: Process, Design, and Applications
Abstract
The injection mold is a high precision tool responsible for the production of most plastic parts used everywhere. Its design is considered critically important for the quality of the product and efficient processing, as well as determinant for the economics of the entire injection molding process. However, typically, no formal engineering analysis is carried out during the mold design stage. In fact, traditionally, designers rely on their skills and intuition, following a set of general guidelines. This does not ensure that the final mold design is acceptable or the best option. At the same time, mold makers are now highly pressured to shorten both leading times and cost, as well as to accomplish higher levels of mold performance. For these reasons, it is imperative to adopt new methods and tools that allow for faster and higher integrated mold design. To that end, a new global approach, based on the integration of well-known quantitative techniques, such as Design for Six Sigma (DFSS), Structural Equation Modeling (SEM), Axiomatic Design (AD) and Multidisciplinary Design Optimization (MDO) is presented. Although some of these methods have been largely explored, individually or in combination with other methodologies, a quantitative integration of all aspects of design, in such a way that the whole process becomes logical and comprehensible, has not yet been considered. To that end, the DFSS methodology, through its IDOV roadmap, was adopted. It is based on the ICOV Yang and El-Haik proposal, establishing four stages for the design process: Identify, which aims to define customers' requirements/expectations; Design, where the creation of a product concept, and its system-level design, is performed; Optimization, in which all the detailed design, through product optimization, is handled; and finally, Validation, where all product design decisions are validated, in order to verify if the new designed entity indeed meets customer and other requirements. As a result, this approach tackles the design of an injection mold in a global and quantitative approach, starting with a full understanding of customer requirements and converting them into optimal mold solutions. In order to validate it, an integrated platform was developed, where all different analysis modules were inserted and optimized through an overseeing code system. The results attained highlight the great potential of the proposed framework to achieve mold design improvements, with consequent reduction of rework and time savings for the entire mold design process.
2011
Autores
Nunes, AA; Galvao, T; Falcao e Cunha, JFE; Pitt, JV;
Publicação
13TH IEEE INTERNATIONAL CONFERENCE ON COMMERCE AND ENTERPRISE COMPUTING (CEC 2011)
Abstract
Public transport users are increasingly connected in real time through mobile devices to social networks, such as Twitter and Facebook. This allows them both to access and to provide valuable operational and emotional information from and to fellow travellers. Transport network management could benefit from this exchange, and also participate by providing rewards to valuable contributors. This paper introduces a model for such cooperative exchanges of information and proposes a valuation system for the information provided and obtained. Users and automatic systems (sensors) would provide information, such as punctuality, noise levels, and assessments of driver's skills, referenced to particular vehicles, routes and times. Then other users accessing such information would classify it on the level of correctness and usefulness, under a validation scheme operated by the transport network management. Such information could either be openly available or private in some degree within a social network, taking account of security aspects that need to be preserved. In a mature environment, more valuable information could only be made available via subscription or freely available to highly valued contributing users. The use of social networks would provide an easy way of sharing information and also provide a sense of community to the involved travellers. Transport network management benefiting from relevant information exchanges could reward users contributing with valuable data, as an incentive to enhance participation. In this context, the information exchanged would achieve a real transactional value and present a new electronic commerce paradigm. Overall, such exchange could also be seen as a serious game.
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