CEGI - Other Publications

Permanent URI for this collection

http://localhost:4000/handle/123456789/263

Browse

Browsing CEGI - Other Publications by Title

  • Item
    Combining the principles of variable neighborhood decomposition search and the fix&optimize heuristic to solve multi-level lot-sizing and scheduling problems
    ( 2013) Seeanner,F ; Bernardo Almada-Lobo ; Meyr,H
    In this paper a new heuristic is proposed to solve general multi-level lot-sizing and scheduling problems. The idea is to cross-fertilize the principles of the meta-heuristic Variable Neighborhood Decomposition Search (VNDS) with those of the MIP-based Fix&Optimize heuristic. This combination will make it possible to solve the kind of problems that typically arise in the consumer goods industry due to sequence-dependent setups and shifting bottlenecks. In order to demonstrate the strength of this procedure, a GLSP variant for multiple production stages is chosen as a representative. With the help of artificial and real-world instances, the quality of the solution as well as the computational performance of the new procedure is tested and compared to a standard MIP-solver.
  • Item
    Cutting and packing
    ( 2013) Bennell,JA ; José Fernando Oliveira ; Waescher,G
  • Item
    The Dotted-Board Model: A new MIP model for nesting irregular shapes
    ( 2013) Toledo,FMB ; Maria Antónia Carravilla ; Cristina Ribeiro ; José Fernando Oliveira ; António Miguel Gomes
    The nesting problem, also known as irregular packing problem, belongs to the generic class of cutting and packing (C&P) problems. It differs from other 2-D C&P problems in the irregular shape of the pieces. This paper proposes a new mixed-integer model in which binary decision variables are associated with each discrete point of the board (a dot) and with each piece type. It is much more flexible than previously proposed formulations and solves to optimality larger instances of the nesting problem, at the cost of having its precision dependent on board discretization. To date no results have been published concerning optimal solutions for nesting problems with more than 7 pieces. We ran computational experiments on 45 problem instances with the new model, solving to optimality 34 instances with a total number of pieces ranging from 16 to 56, depending on the number of piece types, grid resolution and the size of the board. A strong advantage of the model is its insensitivity to piece and board geometry, making it easy to extend to more complex problems such as non-convex boards, possibly with defects. Additionally, the number of binary variables does not depend on the total number of pieces but on the number of piece types, making the model particularly suitable for problems with few piece types. The discrete nature of the model requires a trade-off between grid resolution and problem size, as the number of binary variables grows with the square of the selected grid resolution and with board size.
  • Item
    Equilibria on a Game with Discrete Variables
    ( 2014) João Pedro Pedroso ; Smees,Yves
  • Item
    Glass container production scheduling through hybrid multi-population based evolutionary algorithm
    ( 2013) Motta Toledo,CFM ; Arantes,MD ; Ribeiro de Oliveira,RRR ; Bernardo Almada-Lobo
    Driven by a real-world application in the capital-intensive glass container industry, this paper provides the design of a new hybrid evolutionary algorithm to tackle the short-term production planning and scheduling problem. The challenge consists of sizing and scheduling the lots in the most cost-effective manner on a set of parallel molding machines that are fed by a furnace that melts the glass. The solution procedure combines a multi-population hierarchically structured genetic algorithm (GA) with a simulated annealing (SA), and a tailor-made heuristic named cavity heuristic (CH). The SA is applied to intensify the search for solutions in the neighborhood of the best individuals found by the GA, while the CH determines quickly values for a relevant decision variable of the problem: the processing speed of each machine. The results indicate the superior performance of the proposed approach against a state-of-the-art commercial solver, and compared to a non-hybridized multi-population GA.
  • Item
    Lot sizing versus batching in the production and distribution planning of perishable goods
    ( 2013) Pedro Amorim ; Belo Filho,MAF ; Toledo,FMB ; Almeder,C ; Bernardo Almada-Lobo
    Joint production and distribution planning at the operational level has received a great deal of attention from researchers. In most industries these processes are decoupled by means of final goods inventory that allow for a separated planning of these tasks. However, for example, in the catering industry, an integrated planning framework tends to be more favorable due to the perishable nature of the products that forces a make-to-order production strategy. So far this planning problem has only been addressed by allowing the batching of orders. The main contribution of this paper is to extend this approach and prove the importance of lot sizing for make-to-order systems when perishability is explicitly considered. The value of considering lot sizing versus batching is further investigated per type of production scenario. Overall, results indicate that lot sizing is able to deliver better solutions than batching. On average, for the improved instances, the cost savings ascend to 6.5% when using lot sizing. The added flexibility of lot sizing allows for a reduction on production setup costs and both fixed and variable distribution costs. The savings derived from lot sizing are enhanced by customer oriented time windows and production systems with non-triangular setups. © 2013 Elsevier B.V.
  • Item
    Operations research in agriculture: Better decisions for a scarce and uncertain world
    ( 2013) Maria Antónia Carravilla ; José Fernando Oliveira
    Operations Research/Management Science (OR/MS) can be described as the discipline of applying advanced analytical methods to help making better decisions and has been around in the agricultural and forestry management sectors since the fifties, approaching decision problems that range from more strategic sectorlevel planning to farm operation issues and integrated supply chain management. In this paper insights are given on the use of OR/MS in agriculture, illustrating them with cases drawn from the literature on this topic while keeping the descriptions accessible to uninitiated readers. The presence of OR/MS in Agriculture and Forest Management applications is already extensive but the potential for development is huge in times where resources are becoming increasingly scarce and more has to be done with less, in a sustainable way.
  • Item
    Pricing, relaxing and fixing under lot sizing and scheduling
    ( 2013) Luís Guimarães ; Klabjan,D ; Bernardo Almada-Lobo
    We present a novel mathematical model and a mathematical programming based approach to deliver superior quality solutions for the single machine capacitated lot sizing and scheduling problem with sequence-dependent setup times and costs. The formulation explores the idea of scheduling products based on the selection of known production sequences. The model is the basis of a matheuristic, which embeds pricing principles within construction and improvement MIP-based heuristics. A partial exploration of distinct neighborhood structures avoids local entrapment and is conducted on a rule-based neighbor selection principle. We compare the performance of this approach to other heuristics proposed in the literature. The computational study carried out on different sets of benchmark instances shows the ability of the matheuristic to cope with several model extensions while maintaining a very effective search. Although the techniques described were developed in the context of the problem studied, the method is applicable to other lot sizing problems or even to problems outside this domain.
  • Item
    Time Automaton: A visual mechanism for temporal querying
    ( 2013) Certo,L ; Teresa Galvão ; José Luís Borges
    Available visual temporal querying tools do not provide the means for formulating complex temporal queries. For these queries users have to adopt text-based querying languages, such as SQL. The problem, however, is that using text-based languages is less comfortable than using visual tools and, most important, in some cases temporal queries can be extremely difficult to formulate for users that do not possess programming competences. In this paper we propose the Time Automaton, a highly flexible visual mechanism that enables the formulation of a large set of different types of temporal queries, ranging from the simple to the most complex ones. To prove its practical application we created a tool that implements the mechanism and used it to analyze a real dataset. Time Automaton was validated against a representative sample of temporal queries extracted from the matured OWL-Time Ontology. In order to understand if users, with or without programming competences, could understand and use the Time Automaton we conducted a usability experiment.
  • Item
    Towards a holistic approach to the travel experience: A qualitative study of bus transportation
    ( 2013) Rui Carreira ; Lia Patrício ; Jorge,RN ; Magee,C ; Hommes,QV
    This article presents the results of a qualitative study with 49 bus passengers in two types of mid-distance journeys: (1) experience-centric trips (touristic), and (2) utilitarian trips (intercity transportation). Study results show that passenger travel experience encompasses all moments of contact with the transportation service, as well as aspects that are not in direct control of the transportation provider. The results also reveal that the travel experience involves a holistic set of customer responses that go beyond cognitive assessments, also comprising sensorial and emotional components. The comparison of the two transportation settings shows that both experience-centric and utilitarian trip passengers have a holistic view of the travel experience, although focusing on different experience drivers and customer responses. These findings indicate that transport providers and planners should pay attention to the overall customer travel experience from a holistic view, and that transportation services should be carefully designed and managed in a systemic way.
  • Item
    Understanding participation in company social networks
    ( 2013) Martins,CS ; Lia Patrício
    Purpose - This article seeks to contribute to a better understanding of company social networks (CSNs), which constitute people connected to a company or brand through a social networking site. To this end, the research addresses both participation goals and CSN attributes that drive participation in CSNs. Design/methodology/approach - With a grounded theory approach, this research begins with an exploratory study of the page maintained by a large retailer for six months, followed by a qualitative study featuring in-depth individual interviews and focus groups with 26 members of the CSN. Findings - The results highlight differences between CSNs and other types of online communities (OCs). Members rely on the company to help them achieve their goals; few count on their CSN peers, with whom they maintain weak ties. Unlike in brand communities (BCs), most members are not enthusiasts but instead engage in a pragmatic relationship with the brand. Practical implications - CSNs can create value for both the host company and its members; active management is necessary to unlock that potential. The implications for CSN management include strategies to foster participation and increase value for companies and members. Originality/value - Although the previous research has studied OCs, specific research on CSNs is scarce. This study characterizes CSNs and provides details regarding participation factors in this new context, as well as relevant implications for CSN management and service research.
  • Item
    Unit commitment with valve-point loading effect
    ( 2014) João Pedro Pedroso ; Kubo,Mikio ; Ana Viana