Iterative restricted space search : a solving approach based on hybridization

Face à la complexité qui caractérise les problèmes d'optimisation de grande taille l'exploration complète de l'espace des solutions devient rapidement un objectif inaccessible. En effet, à mesure que la taille des problèmes augmente, des méthodes de solution de plus en plus sophistiquées sont exigées afin d'assurer un certain niveau d 'efficacité. Ceci a amené une grande partie de la communauté scientifique vers le développement d'outils spécifiques pour la résolution de problèmes de grande taille tels que les méthodes hybrides. Cependant, malgré les efforts consentis dans le développement d'approches hybrides, la majorité des travaux se sont concentrés sur l'adaptation de deux ou plusieurs méthodes spécifiques, en compensant les points faibles des unes par les points forts des autres ou bien en les adaptant afin de collaborer ensemble. Au meilleur de notre connaissance, aucun travail à date n'à été effectué pour développer un cadre conceptuel pour la résolution efficace de problèmes d'optimisation de grande taille, qui soit à la fois flexible, basé sur l'échange d'information et indépendant des méthodes qui le composent. L'objectif de cette thèse est d'explorer cette avenue de recherche en proposant un cadre conceptuel pour les méthodes hybrides, intitulé la recherche itérative de l'espace restreint, ±Iterative Restricted Space Search (IRSS)>>, dont, la principale idée est la définition et l'exploration successives de régions restreintes de l'espace de solutions. Ces régions, qui contiennent de bonnes solutions et qui sont assez petites pour être complètement explorées, sont appelées espaces restreints "Restricted Spaces (RS)". Ainsi, l'IRSS est une approche de solution générique, basée sur l'interaction de deux phases algorithmiques ayant des objectifs complémentaires. La première phase consiste à identifier une région restreinte intéressante et la deuxième phase consiste à l'explorer. Le schéma hybride de l'approche de solution permet d'alterner entre les deux phases pour un nombre fixe d'itérations ou jusqu'à l'atteinte d'une certaine limite de temps. Les concepts clés associées au développement de ce cadre conceptuel et leur validation seront introduits et validés graduellement dans cette thèse. Ils sont présentés de manière à permettre au lecteur de comprendre les problèmes que nous avons rencontrés en cours de développement et comment les solutions ont été conçues et implémentées. À cette fin, la thèse a été divisée en quatre parties. La première est consacrée à la synthèse de l'état de l'art dans le domaine de recherche sur les méthodes hybrides. Elle présente les principales approches hybrides développées et leurs applications. Une brève description des approches utilisant le concept de restriction d'espace est aussi présentée dans cette partie. La deuxième partie présente les concepts clés de ce cadre conceptuel. Il s'agit du processus d'identification des régions restreintes et des deux phases de recherche. Ces concepts sont mis en oeuvre dans un schéma hybride heuristique et méthode exacte. L'approche a été appliquée à un problème d'ordonnancement avec deux niveaux de décision, relié au contexte des pâtes et papier: "Pulp Production Scheduling Problem". La troisième partie a permit d'approfondir les concepts développés et ajuster les limitations identifiées dans la deuxième partie, en proposant une recherche itérative appliquée pour l'exploration de RS de grande taille et une structure en arbre binaire pour l'exploration de plusieurs RS. Cette structure a l'avantage d'éviter l'exploration d 'un espace déjà exploré précédemment tout en assurant une diversification naturelle à la méthode. Cette extension de la méthode a été testée sur un problème de localisation et d'allocation en utilisant un schéma d'hybridation heuristique-exact de manière itérative. La quatrième partie généralise les concepts préalablement développés et conçoit un cadre général qui est flexible, indépendant des méthodes utilisées et basé sur un échange d'informations entre les phases. Ce cadre a l'avantage d'être général et pourrait être appliqué à une large gamme de problèmes

Planejamento da etapa de aquisição da cadeia de suprimentos da indústria florestal : aplicação em indústria canadense

Orientador : Prof. José Eduardo Pécora Junior PhDDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia de Produção. Defesa: Curitiba, 25/02/2016Inclui referências : f. 84-92Área de concentração: Pesquisa operacionalResumo: A indústria florestal possui importante papel em diversos países. No Brasil o setor florestal foi responsável por aproximadamente $10 bilhões do total das exportações nacionais e no Canadá por cerca de$ 29 bilhões. No entanto, como outros setores, a indústria florestal sofreu com o impacto gerado pelas incertezas da economia global e enfrenta o declínio dos meios de comunicação baseados em papel. Para que os índices obtidos pelo setor continuem a melhorar, a constante busca pela racionalização do uso de recursos na cadeia de suprimentos desta indústria é necessária. Para alcançar este objetivo, há mais de 50 anos a indústria florestal faz uso de técnicas da Pesquisa Operacional para o planejamento e otimização de sua cadeia, seja para melhorar o manejo ou tornar mais eficiente, por exemplo, a entrega de produtos para clientes. O presente trabalho tem por objetivo auxiliar no planejamento da etapa de aquisição de matéria-prima da cadeia de suprimentos de uma empresa produtora de polpa e papel, localizada na Província de Québec, Canadá, minimizando custos relacionados a esta etapa, como custos de transporte, abertura de estoques e manuseio de carga nos mesmos. Propõe-se para tanto, um modelo de programação linear inteira misto, que considera em sua formulação os efeitos causados pelas políticas de restrição de carga impostas pelo governo provincial durante o período de degelo, bem como a influência da redução do teor de umidade na madeira causado pela secagem ao ar livre, durante seu armazenamento em estoques nos custos de transporte. O modelo proposto foi implementado na linguagem C++ e sua solução obtida pelo solver CPLEX. Os resultados obtidos foram comparados ao modelo de transporte tradicional a fim de avaliar sua qualidade. Em todas as instâncias testadas o modelo proposto alcançou um custo total menor que o modelo de transporte, com baixo tempo de processamento, atingindo sempre o valor ótimo.Abstract: Forestry industry plays an important role in several countries. In Brazil, the forest sector accounted for approximately $10 billion of total national exports and about$ 29 billion in Canada. However, like many other industry sectors, the forestry industry felt the effects of the world's economic downturn and have faced the decline of the paper-based communication products.In order to continue evolve the results obtained by the forest industry the rational use of resources in its supply chain is required. To meet this goal, for over 50 years the forest industry makes use of Operations Research techniques for planning and optimizing its supply chain, as for example to improve the forest management or make the product delivery process more efficient. The present work aims to assist at the procurement stage of supply chain planning of a pulp and paper company, based in the province of Quebec, Canada, in order to minimize costs encountered during this stage, such as transport, handling and stockyards opening costs. We propose a mixed integer linear programming model, which incorporates in its formulation the effects of the weight restriction zones, imposed during the thawing periods by the Quebec's government and the reduction of the wood moisture caused by the air drying effect, on the transportation costs. The proposed model was implemented using C++ programing language and solved with CPLEX. Results obtained with computational experiments were compared with results achieved by the traditional transportation model, in order to evaluate the model quality. In every tested instance, the proposed model reached lower costs when compared to the transportation model, with low computational times, always reaching the solutions global optimum

O problema de roteamento periódico e capacitado em arcos com movimentos contínuos

Orientador: Prof. Dr. Cassius Tadeu ScarpinCoorientador: Prof. Dr. José Eduardo Pécora JuniorTese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Métodos Numéricos em Engenharia. Defesa : Curitiba, 22/10/2018Inclui referências: p.128-134Área de concentração: Programação MatemáticaResumo: Esse trabalho aborda o Problema de Roteamento Periódico e Capacitado em Arcos, Periodic Capacitated Arc Routing Problem (PCARP), que pode ser definido como um problema de roteamento em arcos envolvendo um horizonte de tempo composto por mais de um período, os quais podem ser formados por qualquer fração temporal desde que discretas. Um ou mais veículos, ao fazerem suas rotas, devem executar da melhor maneira possível as tarefas que estão associadas a cada arco sem exceder sua capacidade e respeitando as frequências exigidas. Esse trabalho visa classificar as pesquisas acerca do PCARP por meio de uma proposta taxonômica que considera características físicas, foco aplicável ou teórico e abordagem resolutiva. Outra contribuição é um estudo aplicado à inspeção de ferrovias, o qual é classificado como PCARP com Movimentos Contínuos. Rotas com movimentos contínuos são caracterizadas por não terem a obrigatoriedade de serem iniciadas e terminadas em um depósito. O problema tem sua formulação matemática apresentada e sua a resolução é feita utilizando métodos exato, heurístico e híbridos. O método exato consiste na utilização de um solver comercial e a heurística utilizada é um novo algoritmo de Otimização de Colônia de Formigas, Ant Colony Optimization (ACO). Ambos têm seus pontos fortes que se complementam, sendo assim foram propostas três abordagens híbridas. A primeira consiste na utilização da colônia de formigas como solução inicial para o modelo exato, e as outras duas abordagens são variações do algoritmo Busca Iterativa em Espaço Restrito, Iterative Restricted Space Search (IRSS). A IRSS é baseada na exploração estratégica do espaço de soluções de um dado problema que, nesse trabalho, será auxiliada pelo algoritmo ACO. Os resultados alcançados mostram que as estratégias de resolução propostas são capazes de superar os resultados alcançados pelo solver comercial. Palavras-chave: Problema de Roteamento Periódico e Capacitado em Arcos 1. Movimentos Contínuos 2. Otimização da Colônia de Formigas 3. Busca Iterativa em Espaço Restrito 4. Manutenção e Inspeção de Ferrovias 5.Abstract: The Periodic Capacitated Arc Routing Problem (PCARP) can be defined as an arc routing problem that involves a time horizon, which is greater than one period that can be composed by any fraction of time. One or many vehicles, while into routes, must perform, in the best way possible, all tasks in the arcs without exceeding their capacities and attending the required frequencies. This work classifies researches about PCARP using a taxonomy that considers physical features, applied or academic focus and resolution approach. An additional contribution is a study based on inspection of railroads; this one is classified as PCARP with Continuous Moves. Routes with continuous moves do not need a depot as a starting or finishing point. This work presents the mathematical formulation for the problem and tackles it with exact, heuristic and hybrid methods. The exact approach consists of the use of a commercial solver, and the heuristic is a new Ant Colony Optimization (ACO) algorithm. Both have strengths that may be combined to compose hybrid approaches, three of them are explored. The first one uses the ACO to form an initial solution to the solver, and the two others are variants of the Iterative Restricted Space Search (IRSS) framework. The IRSS strategically exploits the solution space of one problem assisted by an algorithm, in this case, the ACO. The results achieved showed that the strategies proposed are able to overcome the ones from the commercial solver. Keywords: Periodic Capacitated Arc Routing Problem 1. Continuous Moves 2. Ant Colony Optimization 3. Iterative Restricted Space Search 4. Inspection and Maintenance in Railways 5

Density Measurement of Multiphase Pipe Flows

Density is an important physical property and its measurement has wide application in a vast number of industries including; oil and gas, petrochemical, pharmaceutical, brewing, food & beverage production and mining. Density is often required to be accurately measured either as a standalone property or in combination with other flow properties for the purpose of quality assessment, process control, and custody transfer. Given the increasing importance of density measurement, extensive research has been conducted over recent years to develop newer and more accurate density measurement sensors and to improve the accuracy of existing sensors. This thesis describes the design and development of a novel, non-invasive, non-radioactive Vibrating Density Measurement System (VDMS) capable of measuring fluid density in both single phase and multiphase flows. The device is also capable of measuring mean in-situ phase volume fractions in two-phase flows. The VDMS comprises three sub-units; (i) a measurement unit which includes a straight length of sensing pipe with corrugated bellows at both ends, an actuator and relevant sensors; (ii) a signal conditioning and processing unit; and (iii) a data acquisition unit. The thesis also reports the development of a novel mathematical density prediction model which is used in conjunction with the VDMS. It then goes on to report the results of static bench test experiments that were conducted on the VDMS using a bespoke test rig. These tests were performed (i) to obtain the mass of the sensing pipe, its stiffness constant and damping constant; (ii) to investigate the frequency response characteristics of the VDMS; (iii) to obtain the VDMS constant; (iv) to investigate the sensing pipe displacement pattern; (v) to investigate the capability of the VDMS to give accurate density measurements of static fluids and (vi) to define the optimal VDMS operating conditions. Computation of density was achieved using the VDMS, the density prediction model and a novel signal processing technique. This signal processing technique used the Discrete Fourier Transforms (DFTs) of the measured force, used to mechanically excite the sensing pipe at its centre, and the measured displacement at the sensing pipe centre. Next, the thesis reports a novel computer based control system that was developed to ensure that the VDMS automatically operated at its optimal operating conditions, so that errors in the density measurement were minimised. The control system was also capable of providing online computation of the flow mixture density. Results are reported of several experiments conducted by the author on the VDMS to measure the fluid density in a range of “water only” flows, “solids-in-water” flows and “air-in-water” flows. These flows were all vertically upward and were established in the working section of a multiphase flow loop. These multiphase flow experiments were subsequently extended to compute the mean in-situ phase volume fraction of the solids phase in “solids-water” flows and the gas phase in “air-water” flows. For the “water only” and “solids-water” flow experiments, the mean error in the predicted density was consistently within 0.5% of the reference density and the standard deviation of the error was less than 1%. For “air-in-water” flows the predicted density was within 1% of the reference density for flows where the air volume fraction in the mixture was less than 10%. The mean in-situ volume fractions, measured by the VDMS, of the dispersed solids in “solids-in-water” flows and of the dispersed air in “air-in-water” flows were within 10% of the reference measurements for the vast majority of measurements taken. Finally, the thesis describes a modified mathematical model, used with the VDMS, for predicting mixture density in “air-in-water” flows. This modified model is extended to make use of the predicted coupling stiffness between the VDMS sensing pipe and the multiphase mixture. The modified model gave density measurements with a higher order of accuracy than the earlier model which did not consider the effect of the flow compressibility on the coupling between the sensing pipe and the pipe contents