Models and advanced optimization algorithms for the integrated management of logistics operations

Tese de Doutoramento em Engenharia Industrial e de Sistemas.In this thesis, we propose a set of algorithms regarding real combinatorial optimization problems in the context of transportation of goods. These problems consist in the combination of the vehicle routing problem with the two-dimensional bin-packing problem, which is also known as the vehicle routing problem with two-dimensional loading constraints. We also analyzed two related problems, namely the elementary shortest path and the vehicle routing problem with mixed linehauls and backhauls. In both problems, two-dimensional loading constraints are explicitly considered. Two column generation based approaches are proposed for the vehicle routing problem with two-dimensional constraints. The rst one relies on a branch-and-price algorithm with di erent branching schemes. A family of dual valid inequalities is also de ned, aiming to accelerate the convergence of the algorithm. The second approach is based on a set of di erent heuristics strategies, which are applied to the reformulated model. The elementary shortest path problem with two-dimensional constraints is addressed due to its importance in solving the subproblem of the column generation algorithms. To the best of our knowledge, we contribute with the rst approach for this problem, through di erent constructive strategies to achieve feasible solutions, and a variable neighborhood search algorithm in order to search for improved solutions. In what concerns the vehicle routing problem with mixed linehaul and backhauls and two-dimensional loading constraints, di erent variable neighborhood search algorithms are proposed. These algorithms explored various neighborhood structures, being some of those developed based on the features of the problem. All the proposed methods were implemented and experimentally tested. An exhaustive set of computational tests was conducted, using, for this purpose, a large group of benchmark instances. In some cases, a large set of benchmark instances was adapted in order asses the quality of the proposed models. All the obtained results are presented and discussed.Nesta tese, propomos um conjunto de algoritmos sobre problemas reais de otimiza c~ao combinat oria no contexto do transporte de bens. Estes problemas consistem na combina c~ao do problema de planeamento de rotas de ve culos com o problema de empacotamento bidimensional, que tamb em e conhecido como o problema de planeamento de rotas de ve culos com restri c~oes de carregamento bidimensional. Analisamos tamb em dois problemas relacionados, nomeadamente o problema de caminho mais curto e o problema de planeamento de rotas ve culos com entregas e recolhas indiferenciadas. Em ambos os problemas, s~ao explicitamente consideradas restri c~oes de carregamento bidimensional. Duas abordagens baseadas em gera c~ao de colunas s~ao propostas para o problema de planeamento de rotas de ve culos com restri c~oes de carregamento bidimensional. O primeiro baseia-se num algoritmo de parti c~ao e gera c~ao de colunas com diferentes estrat egias de parti c~ao. Uma fam lia de desigualdades duais v alidas e tamb em apresentada, com o objetivo de acelerar a converg^encia do algoritmo. A segunda abordagem baseia-se num conjunto de diferentes estrat egias heur sticas, que s~ao aplicadas ao modelo reformulado. O problema do caminho mais curto com restri c~oes de carregamento bidimensional e abordado devido a sua import^ancia na resolu c~ao do subproblema dos aos algoritmos de gera c~ao de colunas. De acordo com o nosso conhecimento, contribu mos com a primeira abordagem para este problema, atrav es de diferentes estrat egias construtivas para obter solu c~oes v alidas, e um algoritmo de pesquisa em vizinhan ca vari avel, com o objetivo de encontrar solu c~oes de melhor qualidade. No que concerne ao problema de planeamento de rotas de ve culos com entregas e recolhas indiferenciadas, diferentes algoritmos de pesquisa em vizinhan ca vari avel s~ao propostos. Estes algoritmos exploram v arias estruturas de vizinhan ca, sendo algumas destas desenvolvidas com base nas caracter sticas do problema. Todos os m etodos propostos foram implementados e testados experimentalmente. Um extenso conjunto de testes computacionais foi efetuado, utilizando um grande grupo de inst^ancias descritas na literatura. Em alguns casos, um grande conjunto de inst^ancias descritas na literatura foi adaptado com o objetivo de avaliar a qualidade dos m etodos propostos

An exact optimization approach for personnel scheduling problems in the call center industry

Nowadays, the importance of the call center industry is increasing because they are a major means of communication between organizations and their customers. So, ensuring optimized personnel schedules in call centers has several advantages, such as reduced total labor costs, overstaffing, increased employee satisfaction, and acceptable waiting times. In this paper, we address the personnel scheduling problem in a 24/7 call center where the scheduling process is done manually. So, the main goal is to explore exact solution approaches to achieve better solutions while reducing the processing time. The proposed optimization model is an Integer Programming model to assign shifts to workers while minimizing the total penalization associated with employees’ time preferences. The model is tested with several instances, including randomly generated and real-world data instances. The quality of the model is assessed through a computational study of its linear relaxation, concluding that the model presents null integrality gaps in all the tested instances. Additionally, to evaluate the performance of the model when running large instances, several randomly generated instances were tested, achieving good computational results.This work has been supported by FCT – Fundação para a Ciência e a Tecnologia within the R&D Units Project Scope UIDB/00319/2020

Smart and parallel general variable neighborhood search for the pollution-routing problem

This work addresses a new approach to the Pollution-Routing Problem (PRP), a variant of the Vehicle Routing Problem (VRP) under environmental concerns, which includes costs associated with fuel, drivers, and greenhouse gas emissions. The many factors impacting the environment and, simultaneously, the real cost of the routes are usually ignored in the approaches defined to solve routing problems since the total distance traveled remains the standard objective. However, in pollution-routing problems, these elements play an essential role and each one is significantly influenced by the vehicle load and/or speed over the pathways which are followed. To contribute with methods that can provide solutions within an acceptable computational time, we explore local search and meta-heuristic based approaches, with emphasis on a Smart and Parallel General Variable Neighborhood Search algorithm for the PRP. Innovative neighborhood structures allowing continuous speed values in the arcs were a implemented. Additionally, we incorporate parallel programming strategies. To evaluate the effectiveness of these strategies, we report on the computational experiments conducted on benchmark instances, and we compare the results obtained with other studies from the literature.The first author has been supported by FCT – Fundac¸ao para a Ciência e Tecnologia, through national funds from MCTES – Ministerio da Ciência, Tecnologia e Ensino Superior, and by European Social Fund through NORTE2020 – Programa Operacional Regional Norte, within the research grant SFRH/BD/146217/2019. This work has been supported by FCT – Fundação para a Ciencia e a Tecnologia within the R&D Units Project Scope: UIDB/00319/2020

Optimization algorithms for integrated processes in industry 4.0

Evidence of an increasingly dynamic market forces companies to look for new ways to respond, given that traditional supply chain management systems are increasingly more vulnerable in their needs. In this sense, we have seen a paradigm shift at the industrial level with the emergence of new concepts from Industry 4.0 to improve productivity and process efficiency. However, their implementation in companies can be an expensive and time-consuming process, particularly for small and medium-sized enterprises. This work presents a perspective for optimization algorithms in the context of Industry 4.0. With new methods and models, simultaneously integrating traditional supply chain processes, it is possible to find good solutions (globally optimal), in real time and with an investment cost more proportional to the reality of each company. It may, therefore, be an alternative to mitigate the discrepancy between companies of quite different sizes.This work has been supported by FCT - Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020 and by FEDER funds through the program COMPETE – Programa Operacional Factores de Competitividade – and by national funds through FCT – Fundação para a Ciência e a Tecnologia –, under the project UIDB/00285/2020

A constructive heuristic for the multi-compartment vehicle routing problem: an approach for a fuel distribution company

In this paper, we suggest a Decision Support System (DSS) for route planning. This DSS was developed in a real context in a fuel distribution company. This company distributes three types of fuel through multi-compartment vehicles with limited capacity, and satisfying delivery time windows imposed by the customers. Two approaches for this problem were considered: The first one considers the route planning without replenishments while the second one considers the multi-trip case. The solution method is based on a Clarke and Wright savings algorithm incorporating all the constraints referred to above. Both approaches were tested using real instances. The savings for the company, in terms of the distribution process, were identified in the computational results. The DSS may provide an effective support to a complex decision problem.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013.info:eu-repo/semantics/publishedVersio

Gestão ambiental na indústria da cortiça

Mestrado em Engenharia do AmbienteNas últimas décadas tem-se verificado uma degradação contínua do meio ambiente, intensificada pela produção em massa das indústrias, aliado a um crescente consumismo da sociedade. Atualmente, as organizações e a sociedade civil demonstram uma crescente preocupação com os problemas ambientais, é neste contexto que surgem as questões associadas aos sistemas de gestão ambiental (SGA), como forma de integrar as preocupações das organizações com a proteção do ambiente. O presente projeto, realizado no âmbito do estágio curricular do Mestrado de Engenharia do Ambiente, pretende explorar e servir de apoio na implementação e desenvolvimento de um Sistema de Gestão Ambiental em duas Unidades Industriais da Amorim & Irmãos, S.A. Para o cumprimento dos objetivos do projeto foi realizada uma revisão bibliográfica da temática Sistemas de Gestão Ambiental, que possibilitou alargar o conhecimento sobre o tema do estágio. A segunda fase do trabalho consistiu na integração nos processos e infraestruturas da empresa. A terceira fase incluiu a realização dos trabalhos práticos necessários para a implementação e desenvolvimento dos Sistemas de Gestão Ambiental. Tendo em conta a metodologia seguida conclui-se que a realização este projeto foi muito vantajosa para todas as partes envolvidas, tendo contribuído: para um grande avanço na implementação e desenvolvimento dos Sistemas de Gestão Ambiental nas duas Unidades Industriais, permitindo assim melhorar os seus desempenhos ambientais; para a aquisição e consolidação de conhecimentos na área e proporcionou uma experiencia que será benéfica no envolvimento de um projeto desta natureza.Over the last few decades we have experienced a continuing deterioration of the environment, intensified by the mass production of the industry sector combined with a growing promotion of consumerism. In nowadays organizations and civil society have showed a growing awareness towards environmental issues. It’s in this context that the questions linked to the Environmental Management Systems EMS, as a way to integrate environment protection in the organizations concerns. This project, carried out in the framework of the curricular internship of the Environmental Engineering masters degree, intends to explore and serve as support on the implementation and development of an Environmental Management System in two industrial unites of Amorim & Irmãos, S.A. Amorim & Irmãos. To the fulfillment of the project objectives was carried out a bibliographic review of the Environmental Management Systems theme, which gave a deeper knowledge about the internship theme. The second stage consisted in the integration into the company processes and infrastructures. The third stage includes the practical processes needed for the implementation and development of the Environmental Management Systems. Taking into account the adopted methodology we can conclude that this project was very beneficial for all the parts involved, having contributed for a great advance in the implementation and development of the Environmental Management Systems of the two industrial units, allowing to improve their environmental performance; to the acquisition and consolidation of knowledge in this area and contributed with an experience that will be beneficial to the involvement into a project of this nature

A matheuristic approach to the integration of three-dimensional Bin Packing Problem and vehicle routing problem with simultaneous delivery and pickup

This work presents a hybrid approach to solve a distribution problem of a Portuguese company in the automotive industry. The objective is to determine the minimum cost for daily distribution operations, such as collecting and delivering goods to multiple suppliers. Additional constraints are explicitly considered, such as time windows and loading constraints due to the limited capacity of the fleet in terms of weight and volume. An exhaustive review of the state of the art was conducted, presenting different typology schemes from the literature for the pickup and delivery problems in the distribution field. Two mathematical models were integrated within a matheuristic approach. One model reflects the combination of the Vehicle Routing Problem with Simultaneous Delivery and Pickup with the Capacitated Vehicle Routing Problem with Time Windows. The second one aims to pack all the items to be delivered onto the pallets, reflecting a three-dimensional single bin size Bin Packing Problem. Both formulations proposed—a commodity-flow model and a formulation of the Three-Dimensional Packing Problem must be solved within the matheuristic. All the approaches were tested using real instances from data provided by the company. Additional computational experiments using benchmark instances were also performed.This research was funded by national funds through FCT—Fundação para a Ciência e a Tecnologia, under the projects UIDB/00285/2020, UIDB/00319/2020. This work was supported by the Research Unit on Governance, Competitiveness and Public Policies (UIDB/04058/2020) + (UIDP/04058/2020), funded by national funds through the Foundation for Science and Technology, IP. This work was also funded by FEDER in the frame of COMPETE 2020 under the project POCI-01-0247-FEDER-072638

Comparison of three control theories for single-phase active power filters

Active Power Filters have been developed in last years, mostly for three-phase systems applications. The use of Shunt Active Power Filters on single-phase facilities brings many benefits for the electrical grid, since these installations have non linear loads and power factor problems, and in their total, they are responsible by a significant portion of the total electric energy consumption. Harmonics and reactive power consumed by single-phase installations cause additional power losses on the electrical grid. So, mitigate harmonics at the origin helps reducing these extra losses and other problems caused by the harmonics. The drawback of this solution is the necessity of a large number of Active Power Filters distributed by the generality of the single-phase facilities. So, it becomes necessary a simple and low cost Shunt Active Power Filter to install on single-phase installations. This paper presents three simple control theories to use on single-phase Shunt Active Power Filters. Simulation and experimental results comparing the three different control theories are presented and analyzed.Fundação para a Ciência e a Tecnologia (FCT