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Publications

Publications by SEM

2018

Integrating pricing and capacity decisions in car rental: A matheuristic approach

Authors
Oliveira, BB; Carravilla, MA; Oliveira, JF;

Publication
OPERATIONS RESEARCH PERSPECTIVES

Abstract
Pricing and capacity decisions in car rental companies are characterized by high flexibility and interdependence. When planning a selling season, tackling these two types of decisions in an integrated way has a significant impact. This paper tackles the integration of capacity and pricing problems for car rental companies. These problems include decisions on fleet size and mix, acquisitions and removals, fleet deployment and repositioning, as well as pricing strategies for the different rental requests. A novel mathematical model is proposed, which considers the specific dynamics of rentals on the relationship between inventory and pricing as well as realistic requirements from the flexible car rental business, such as upgrades. Moreover, a solution procedure that is able to solve real-sized instances within a reasonable time frame is developed. The solution procedure is a matheuristic based on the decomposition of the model, guided by a biased random-key genetic algorithm (BRKGA) boosted by heuristically generated initial solutions. The positive impact on profit, of integrating capacity and pricing decisions versus a hierarchical/sequential approach, is validated.

2018

Collaborative Transformation Systems - Path to Address the Challenges Around the Competitiveness of Mature Countries

Authors
Azevedo, A;

Publication
COLLABORATIVE NETWORKS OF COGNITIVE SYSTEMS

Abstract
In mature countries manufacturing is one of the most significant sources of economic development and growth. In those countries, manufacturing transformation systems will be grounded on seamless collaborative environments and will have a high degree of flexibility in production, in terms of product needs (specifications, quality, design), volume, timing, resource efficiency and cost, being able to adapt to customer needs and make use of the entire network chain for value creation. Future transformations systems will be massively collaborative and will be enabled by a network-centric approach, making use of multidimensional data analytics, driven by advanced ICT and the latest available proven manufacturing technologies.

2018

Planning woody biomass supply in hot systems under variable chips energy content

Authors
Marques, A; Rasinmaki, J; Soares, R; Amorim, P;

Publication
BIOMASS & BIOENERGY

Abstract
The growing economic importance of the biomass-for-bioenergy in Europe motivates research on biomass supply chain design and planning. The temporally and geographically fragmented availability of woody biomass makes it particularly relevant to find cost-effective solutions for biomass production, storage and transportation up to the consumption facility. This paper addresses tactical decisions related with optimal allocation of wood chips from forest residues at forest sites to terminals and power plants. The emphasis is on a "hot-system" with synchronized chipping and chips transportation at the roadside. Thus, decisions related with the assignment of chippers to forest sites are also considered. We extend existing studies by considering the impact of the wood chips energy content variation in the logistics planning. This is a key issue in biomass-for-bioenergy supply chains. The higher the moisture content of wood chips, the lower its net caloric value and therefore, a larger amount of chips is needed to meet the contracted demand. We propose a Mixed Integer Programming (MIP) model to solve this problem to optimality. Results of applying the model in a biomass supply chain case in Finland are presented. Results suggest that a 20% improvement in the supplier profit can be obtained with the proposed approach when compared with a baseline situation that relies on empirical estimates for a fixed and known moisture content in the end of an obliged storage age.

2018

A new load balance methodology for container loading problem in road transportation

Authors
Ramos, AG; Silva, E; Oliveira, JF;

Publication
EUROPEAN JOURNAL OF OPERATIONAL RESEARCH

Abstract
The load balance aspect of the Container Loading Problem (CLP) has been handled in an simplified way in the literature. Either load balance has been treated as a soft constraint or the geometrical centre of the container has been assumed to be the ideal location for the centre of gravity of the cargo, or both, which does not meet regulatory directives and transportation legislation. In this paper, we treat load balance as a 'hard constraint and adopt vehicle specific diagrams that define the feasibility domain for the location of the centre of gravity of the cargo, according to the vehicle specific technical characteristics, thus fulfilling and complying with real-world regulations and legislation. We propose a multi-population biased random-key genetic algorithm (BRKGA), with a new fitness function that takes static stability and load balance into account. Extensive computational experiments were performed with different variants of the proposed approach. Also solutions taken from the literature were evaluated in terms of load balance. The computational results show that it is possible to obtain stable and load balanced solutions without compromising the performance in terms of container volume utilization, and demonstrate also the advantage in incorporating load balance in the packing generation algorithm.

2018

Solving irregular strip packing problems with free rotations using separation lines

Authors
Peralta, J; Andretta, M; Oliveira, JF;

Publication
Pesquisa Operacional

Abstract
Solving nesting problems or irregular strip packing problems is to position polygons on a fixed width and unlimited length strip, obeying polygon integrity containment constraints and non-overlapping constraints, in order to minimize the used length of the strip. To ensure non-overlapping, we use separation lines, i.e., straight lines that separate polygons. We present a nonlinear programming model that considers free rotations of the polygons and of the separation lines. This model uses a considerable smaller number of variables than the few other approaches proposed in the literature. We use the nonlinear programming solver IPOPT (an algorithm of interior points type), which is part of COIN-OR. Computational tests were run using established benchmark instances and the results were compared with the ones obtained with other methodologies in the literature that use free rotations. © 2018 Brazilian Operations Research Society.

2018

Delivery mode planning for distribution to brick-and-mortar retail stores: discussion and literature review

Authors
Martins, S; Amorim, P; Almada Lobo, B;

Publication
FLEXIBLE SERVICES AND MANUFACTURING JOURNAL

Abstract
In the retail industry, there are multiple products flowing from different distribution centers to brick-and-mortar stores with distinct characteristics. This industry has been suffering radical changes along the years and new market dynamics are making distribution more and more challenging. Consequently, there is a pressure to reduce shipment sizes and increase the delivery frequency. In such a context, defining the most efficient way to supply each store is a critical task. However, the supply chain planning decision that tackles this type of problem, delivery mode planning, is not well defined in the literature. This paper proposes a definition for delivery mode planning and analyzes multiple ways retailers can efficiently supply their brick-and-mortar stores from their distribution centers. The literature addressing this planning problem is reviewed and the main interdependencies with other supply chain planning decisions are discussed.

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