Dissertations / Theses on the topic 'Rolling horizons'

In this paper, a job shop scheduling problem with the objective of minimizing work in process (WIP) subject to meeting due dates constraints is evaluated in a rolling horizon setting. An iterative-adaptive deterministic simulation-based procedure is first used to obtain a feasible solution. This procedure, the Virtual Factory, has been shown to provide near-optimal solutions to industrial-sized problems in seconds for the criterion of minimizing maximum lateness, L_max. Then, a simulated annealing post-processing procedure is used to determine when to release jobs to minimize WIP while keeping L_max &#8804 0.

Over the last decade, the semiconductor industry has witnessed a steady increase in its complexity based on improvements in manufacturing processes and equipment. Progress in the technology used is no longer the key to success, however. In fact, the semiconductor technology has reached such a high level of complexity that improvements appear at a slow pace. Moreover, the diffusion of technology among competitors shows that traditional approaches based on technological advances and innovations are not sufficient to remain competitive. A recent crisis in the semiconductor field in the summer 2001 made it even clearer that optimizing the operational control of semiconductor wafer fabrication facilities is a vital key to success. Operating research-oriented studies have been carried out to this end for the last 5 years. None of them, however, suggest a comprehensive model and solution to the operational control problem of a semiconductor manufacturing facility. Two main approaches, namely mathematical programming and dispatching rules, have been explored in the literature so far, either partially or entirely dealing with this problem. Adapting the Shifting Bottleneck (SB) procedure is a third approach that has motivated many studies. Most research focuses on optimizing a certain objective function under idealized conditions and thus does not take into consideration system disruptions such as machine breakdown. While many papers address the adaptations of the SB procedure, the problem of re-scheduling jobs dynamically to take disruptions and local disturbances (machines breakdown, maintenance...) into consideration shows interesting perspectives for research. Dealing with local disturbances in a production environment and analyzing their impact on scheduling policies is a complex issue. It becomes even more complex in the semiconductor industry because of the numerous inherent constraints to take into account. The problem that is addressed in this thesis consists of studying dynamic scheduling in a job-shop environment where local disturbances occur. This research focuses on scheduling a large job shop and developing re-scheduling policies when local disturbances occur. The re-scheduling can be applied to the whole production horizon considered in the instance, or applied to a restricted period T that becomes a decision variable of the problem. The length of the restricted horizon T of re-scheduling can influence significantly the overall results. Its impact on the general performance is studied. Future extensions can be made to include constraints that arise in the semiconductors industry, such as the presence of parallel and batching machines, reentrant flows and the lot dedication problem. The theoretical results developed through this research will be applied to data sets to study their efficiency. We hope this methodology will bring useful insights to dealing effectively with local disturbances in production environments.<br>Master of Science

Neste trabalho, estudamos o problema de corte bidimensional multiperíodo com sobras aproveitáveis, que consiste em cortar objetos grandes visando a produção de um conjunto de itens menores. Supomos um horizonte de planejamento finito com uma quantidade finita de períodos entre os tempos inicial e final. Primeiramente consideramos uma versão determinística em que conhecemos, à priori, os itens solicitados em uma ordem de trabalho e o custo dos objetos a cada período. Algumas das sobras geradas durante o processo de corte dos itens solicitados em um período podem ser utilizadas como objetos no futuro. As sobras que podem ser usadas no futuro são denominadas sobras aproveitáveis. De forma geral, uma sobra é considerada aproveitável se possui dimensões iguais ou superiores as de algum item de uma lista pré-definida para o período. O objetivo é minimizar o custo total dos objetos utilizados para satisfazer a ordem de trabalho dos itens solicitados de todo o horizonte considerado. Havendo soluções com o mesmo custo, desejamos encontrar aquela que, no fim do horizonte de tempo considerado, maximize o valor das sobras aproveitáveis remanescentes. Apresentamos uma modelagem matemática do problema usando uma formulação em dois níveis, que é transformada em um modelo de programação linear inteira mista, devido às características do problema. Considerando a dificuldade em resolver o modelo desenvolvido, apresentamos uma proposta de uma abordagem heurística baseada em Programação Dinâmica Aproximada (PDA) para lidar com o problema proposto. Outras opções baseadas em estratégias do tipo horizonte rolante e relax-and-fix também são consideradas. Consideramos também o cenário onde não conhecemos de antemão os itens da ordem de trabalho e o custo dos objetos, mas temos informações das distribuições de probabilidade de ambos. Nesse caso, apresentamos uma abordagem baseada em programação dinâmica aproximada para estimar a melhor estratégia a ser seguida em cada período. Comparamos os resultados obtidos pela PDA com os resultados encontrados por um método guloso. Em cenários adequados, os resultados mostram que a PDA consegue soluções superiores ao método guloso.<br>In this research, we study the multi-period two-dimensional cutting problem with usable leftover, which consists of cutting objects to produce a set of items. We assume a finite planning horizon with a finite amount of periods between the initial and final times. First we consider a deterministic version in which we know, a priori, the set of ordered items and the cost of the objects at each period. Some of the leftovers generated during the cutting process of the ordered items in a period may be used as objects in the future. The leftovers that can be used in the future are called usable leftovers. In general, a leftover is considered usable if it has dimensions equal to or greater than that of some item from a predefined list for the period. The goal is to minimize the total cost of the objects used to cut the set of ordered items of the entire considered horizon. If there are solutions with the same cost, we wish to find one that, at the end of the considered time horizon, maximizes the value of the remaining usable leftovers. We present a mathematical model of the problem using a bilevel formulation, which is transformed into a mixed integer linear programming model, due to the characteristics of the problem. Considering the difficulty in solving the developed model, we propose a heuristic approach based on approximate dynamic programming (ADP) to deal with the proposed problem. Other options based on the rolling horizon and relax-and-fix strategies are also considered. We also consider the scenario where we do not know in advance the set of ordered items and the cost of the objects, but we have information about the probability distributions of both. In this case, we present an approach based on approximate dynamic programming to estimate the best strategy to be followed at each period. We compared the results obtained by the ADP with the results found by a greedy method. In suitable scenarios, the results show that the ADP achieves superior solutions to the greedy method.

As air traffic congestion grows, air traffic flow management (ATFM) is becoming a great concern. ATFM deals with air traffic and the efficient utilization of the airport and airspace. Air traffic efficiency is heavily influenced by unanticipated factors, or uncertainties, which can come from several sources such as mechanical breakdown; however, weather is the main unavoidable cause of uncertainty. Because weather is unpredictable, it poses a critical challenge for ATFM in current airport and airspace operations. Convective weather results in congestion at airports as well as in airspace sectors. During times of congestion, the decision as how and when to send aircraft toward an airspace sector in the presence of weather is difficult. To approach this problem, we first propose a two-stage stochastic integer program by emphasizing a given single sector. By considering ground delay, cancellation, and cruise speed for each flight on the ground in the first stage, as well as air holding and diversion recourse actions for each flight in the air in the second stage, our model determines how aircraft are sent toward a sector under the uncertainty of weather. However, due to the large number of weather scenarios, the model is intractable in practice. To overcome the intractability, we suggest a rolling horizon method to solve the problem to near optimal. Lagrangian relaxation and subgradient method are used to justify the rolling horizon method. Since the rolling horizon method can be solved in real time, we can apply it to actual aircraft schedules to reduce the costs incurred on the ground as well as in airspace. We then extend our two-stage model to a multistage stochastic program, which increases the number of possible weather realizations and results a more efficient schedule in terms of costs. The rolling horizon method as well as Lagrangian relaxation and subgradient method are applied to this multistage model. An overall comparison among the previously described methodologies are presented.

Les blocs opératoires sont l’un des principaux postes de dépenses du système hospitalier, rationaliser et optimiser leur gestion permet donc une réduction des coûts pour la structure. S’aidant de l’unité de chirurgie orthopédique du CHU d’Angers, nous proposons donc des outils d’aide à la planification des interventions chirurgicales prenant aussi en compte les contraintes liées à la stérilisation d’instruments médicaux tels que les kits d’intervention. Le but de ces outils est de baisser les coûts de fonctionnement des blocs opératoires, optimiser le recours aux heures supplémentaires et les stérilisations de matériels en urgence, etc. Nous considérons premièrement que toutes les données sont connues et nous proposons un modèle de type MILP et une heuristique de construction de solutions dont les résultats obtenus améliorent la planification du CHU. Nous adaptons ensuite une approche permettant d’assimiler l’arrivée dynamique des patients et montrons, résultats à l’appui, que cette technique permettrait d’améliorer le processus de prévision des opérations du bloc, si les durées opératoires sont connues. Cette dernière hypothèse ne tenant pas dans le cas réel, nous suggérons de la lever en proposant de robustifier tout d’abord notre approche statique de deux façons que nous adaptons au cas dynamique. A l’issue de ces travaux, une amélioration de 54% est constatée du processus de planification en termes d’heures supplémentaires tout comme une réduction du nombre de stérilisations à effectuer dans l’urgence (90%) et d’une hausse significative du taux d’occupation des blocs opératoires (5.7%)<br>The operating theater is considered as the most expensive and important resource in hospitals as it counts as the main source of income and expenses. This critical rule and the increase in costs urge hospitals to organize their processes more efficiently and effectively. In this thesis, we will be working with the Centre Hospitalier Universitaire d’Angers (CHU) of Angers in France. We focus on the surgery scheduling problem at the orthopedic surgery unit. The main contribution of this work is the consideration of the activities of the sterilizing unit as a hard constraint and a performancemeasure for the problem. In the first part of this work, we present a multidimensional classification of the current literature on the surgical case scheduling problem. In the second part, we solve the deterministic version of the problem. Starting with the static problem, we propose a MILP and a constructive heuristic and show that the obtained results significantly improve over the ones of the CHU.Next, we solved the deterministic dynamic version by implementing our MILP in a rolling horizon approach. Again, the results were superior to the CHU ones. We then showed that a non-deterministic approach is a must due to the big degradations caused by surgeries duration uncertainties. In the third part, we tackled the non-deterministic version of the problem. Similarly, we started with the static problem and proposed two robust models. Finally, we implement both robust models in a rolling horizon method to solve the dynamic scheduling problem. The results of the both non-deterministic versions show much more robustness compared to the deterministic ones and better values overall

Le service des urgences est un important service de soins qui représente le goulot d'étranglement de l'hôpital. Les urgences sont souvent confrontées à des problèmes de tension dans de nombreux pays à travers le monde. L'une des causes de la tension dans les urgences est l'interférence permanente entre trois types de patients : les patients déjà programmés, les patients non programmés et les patients non programmés urgents. Le but de cette thèse est de contribuer à l'étude et au développement d'un système d’aide à la décision pour améliorer la prise en charge des patients aussi bien en mode de fonctionnement normal qu’en mode tension. Deux principaux processus ont été développé. Un processus d’ordonnancement à horizon glissant en utilisant un algorithme mimétique avec l’intégration des opérateurs génétiques contrôlés pour déterminer un calendrier optimal de passage des patients. Le deuxième processus d’orchestration dynamique, à base d’agents communicants, tient compte de la nature dynamique et incertaine de l'environnement des urgences en actualisant continuellement ce calendrier. Cette orchestration pilote en temps réel le workflow du parcours patient, améliore pas à pas les indicateurs de performance durant l'exécution. Grâce aux comportements des agents et aux protocoles de communication, le système proposé a établi un lien direct en temps réel entre les performances requises sur le terrain et les actions afin de diminuer l'impact de la tension. Les résultats expérimentaux, mis en œuvre au CHRU de Lille, indiquent que l’application de nos approches permet d’améliorer les indicateurs de performance grâce aux pilotage par les agents du workflow en cours exécution<br>The emergency department is an important care service that represents the hospital's bottleneck. Emergencies often face overcrowding problems in many countries worldwide. One of the causes of the emergency department overcrowding is the permanent interference between three types of arriving patients: already programmed patients, non-programmed patients and urgent non-programmed patients. The aim of this thesis is to contribute to the study and development a decision support system to improve patient management in both normal and overcrowding situation. Two main processes have been developed. A rolling-horizon scheduling process using a memetic algorithm with the integration of controlled genetic operators to determine an optimal schedule for patient. The second dynamic orchestration process, based on communicating agents, takes into account the dynamic and uncertain nature of the emergency environment by continually updating this schedule for patient. This orchestration monitoring in real time the workflow of the patient pathway improves step by step the performance indicators during the execution. Through agent behaviors and communication protocols, the proposed system has established a direct real-time link between the required performances and the effective actions in order to decrease the overcrowding impact. The experimental results in this thesis, implemented at the Regional University Hospital Center (RUHC) of Lille, justify the interest of the application of our approaches to improve the performance indicators thanks to the agents driven patient pathway workflows during their execution

I den här vetenskapliga essän: Konsten att vara specialist och kunna lyssna, reflekterar jag kring och undersöker min praktik som yrkesverksam inom HR-området. Jag undersöker några av de förväntningar som jag och min omgivning har på mig och min yrkesroll. Hur gör jag när jag möter motstridiga förväntningar? Hur ska jag förstå mitt agerande? För att synliggöra min praktiska kunskap tar jag hjälp av tre möten med chefer, hämtade ur mitt arbetsliv. Genom dessa möten och frågorna ovan låter jag min yrkesutövning möta modern managementforskning och teorier kring främst tolkning, sammanhang och specialistrollen från filosoferna Paul Feyerabend och Hans-Georg Gadamer. Jag kommer fram till att min praktiska kunskap är att kunna läsa av situationerna och förväntningarna i situationen jag befinner mig och våga stanna i osäkerheten utan att ha svaren givna, jag måste stanna i processen och när jag gör det visar sig även lösningarna. Jag kommer också fram till vikten av att kunna lyssna. En annan viktig insikt är att min roll som HR-medarbetare är beroende av att det är just jag i en viss kontext som utövar mitt yrke och att min person och min roll är intimt sammankopplade i min yrkesutövning. Det går inte att skilja oss åt.<br>In this scientific essay: The art of being a specialist and listening, I reflect and examine my practice as a professional in the area of HR. I examine some of the expectations that I and my surrounding have on me and my professional role. How do I do when I meet conflicting expectations? How should I understand the way I’m acting at work? I retell three situations from meetings with managers taken from my work experience. These stories help me to make my practical knowledge visible. Through these examples, and the questions above I let my profession meet modern management research and theories about interpretation, context and specialist role from the philosophers Paul Feyerabend and Hans-Georg Gadamer. I conclude that my practical knowledge is to read the complexity and expectations in the situation I find myself and dare to remain in uncertainty without having the answers given, I have to stay in the process, and when I do, solutions will be given to me. The importance of being able to listen turns out as an important part of my practical knowledge. Another important insight is that my role as HR employees are dependent on it just me in a certain context practicing my profession and to my person and my role is intimately linked in my profession. You can not separate us.

L’industrie forestière est un secteur qui, même s’il est en déclin, se trouve au cœur du débat sur la mondialisation et le développement durable. Pour de nombreux pays tels que le Canada, la Suède et le Chili, les objectifs sont de maintenir un secteur florissant sans nuire à l’environnement et en réalisant le caractère fini des ressources. Il devient important d’être compétitif et d’exploiter de manière efficace les territoires forestiers, de la récolte jusqu’à la fabrication des produits aux usines, en passant par le transport, dont les coûts augmentent rapidement. L’objectif de ce mémoire est de développer un modèle de planification tactique/opérationnelle qui permet d’ordonnancer les activités pour une année de récolte de façon à satisfaire les demandes des usines, sans perdre de vue le transport des quantités récoltées et la gestion des inventaires en usine. L’année se divise en 26 périodes de deux semaines. Nous cherchons à obtenir les horaires et l’affectation des équipes de récolte aux blocs de coupe pour une année. Le modèle mathématique développé est un problème linéaire mixte en nombres entiers dont la structure est basée sur chaque étape de la chaine d’approvisionnement forestière. Nous choisissons de le résoudre par une méthode exacte, le branch-and-bound. Nous avons pu évaluer combien la résolution directe de notre problème de planification était difficile pour les instances avec un grand nombre de périodes. Cependant l’approche des horizons roulants s’est avérée fructueuse. Grâce à elle en une journée, il est possible de planifier les activités de récolte des blocs pour l’année entière (26 périodes).<br>Forest industry is a sector located at the heart of the debate on globalisation and sustainable development, even if it is in decline. For many countries like Canada, Sweden and Chile, the objectives are to maintain a flourishing sector without damaging the environment and to realize the finite nature of resources. It is important to be competitive and to operate effectively on forest territories, from harvesting to manufacturing products, through transport, in a context where costs increase rapidly. This master’s thesis is developing a tactical operational planning model to organize activities for a year to meet requests for factories, without losing sight of the transport of harvested quantities and inventory management factory. The year is divided into 26 periods of two weeks. We seek harvest teams schedules and assignment to harvest areas (units) for a year. The problem is formulated as a mixed integer programming model, whose structure is based on each stage of the forest supply chain. We choose to solve it by an exact method, branch-and-bound. We were able to assess how the direct resolution of our planning problem was difficult for instances with a large number of periods. However the rolling horizon approach has proved successful. In a day, we obtained the harvest activities planning for 26 periods.

Ce projet de recherche a été réalisé avec la collaboration de FPInnovations. Une part des travaux concernant le problème de récolte chilien a été effectuée à l'Instituto Sistemas Complejos de Ingeniería (ISCI) à Santiago (Chili).<br>La planification de la récolte forestière comporte différents niveaux de planification selon l'horizon de temps du problème et la nature des décisions à prendre. Dans un premier temps, nous nous intéressons à un problème de planification annuelle de la récolte, à mi-chemin entre la planification tactique et opérationnelle. Ce problème appliqué à l'exploitation forestière au Québec, naît d'un besoin de l'industrie québécoise d'un outil pour la planification annuelle intégrée qui fournit aux équipes de récolte leur calendrier. L'intégration consiste à déterminer les affectations des équipes aux blocs en fonction des besoins des usines, et qui respectent les contraintes de transport, de gestion des stocks, et bien entendu les conditions d'exploitation en forêt. Plusieurs modèles de types MIP ont été formulés, des approches de résolution adaptées à la structure de chacun des modèles ont été développées. L'approche par horizon roulant est celle dont les résultats surpassent les deux autres et surtout, améliorent de façon significative les plans usuellement suivis, notamment en réduisant les volumes non livrés aux usines de moitié, ou encore en divisant entre 2 et 6 fois les volumes en stock quand la demande diminue. De plus, le développement d'une interface pour systématiser le processus de résolution et élargir le nombre d'utilisateurs, est la seconde contribution de la thèse. Cette étape du projet correspond à un transfert de technologie de l'université vers l'industrie. Le second problème de planification se situe au Chili, est une planification tactique de la récolte dirigée par les prix et demandes en produits finis, ces derniers étant considérés comme des paramètres aléatoires. Le problème stochastique formulé est résolu suivant une méthode de décomposition par scénarios dont le nombre varie entre 10 et 100. Pour chaque scénario, la solution déterministe, lorsqu'elle est réalisable, est comparée avec celle issue de la résolution du problème stochastique. La solution déterministe n'est réalisable que pour une dizaine de scénarios parmi 100, et les pertes encourues sont en moyenne de 9%.<br>Harvest planning has different levels according to the time horizon of the problem and the nature of the decisions to be taken. Initially, we are interested in an annual harvest scheduling problem, halfway between tactical and operational planning. This problem applied in Qu\'ebec, is motivated by a need from the industry for an integrated tool that provides annual schedules to harvest teams. The integration is to determine demand driven assignments of teams to cutblocks and to manage transportation and inventory accordingly. Several MIP models have been formulated, and three solution approaches have been developed according to the structure of each model. The rolling horizon approach performs better than the other two, by improving significantly from the traditional harvest plan, especially by reducing by half non delivered volumes or by dividing between 2 and 6 times volumes in storage when demands decrease. Another contribution of the thesis is the creation of an interface to systematize solution process and to allow other users. This is the object of a transfer project between academics and industry. The second problem is a Chilean tactical harvest planning. Harvesting decisions are driven by stochastic demands and prices of final products. The stochastic problem is solved using a heuristic based on a scenario decomposition technique. The number of scenarios considered is between 10 and 100 scenarios. For each scenario, when the deterministic solution is feasible, it is compared with the stochastic solution for the current scenario. The deterministic solution is only feasible for 10% of the scenarios, and induces losses of 9% in average.

碩士<br>國立成功大學<br>交通管理學系碩博士班<br>95<br>As the development of logistics, transportation and/or delivering cost, which accounts for substantial proportion of overall cost, could be reduced to enhance the competitiveness of the enterprise. Due to the advancement of Intelligent Transportation Systems (ITS), dispatching centers can get real-time information, real-time requests, and commercial vehicle routes according to electron, communication, and real-time information technology. The application of ITS technologies can improve deliver/pick-up services; however, the critical question is how to solve the Online Vehicle Routing Problems (Online VRP) under real-time information and real-time requests. The Vehicle Routing Problems, one of the NP-hard problems, cannot not be solved efficiently by mathematical programming techniques. Although the heuristic approaches do not guarantee to obtain the optimal solution, they can solve the VRP problem more efficiently. Online VRP consider realistic issues, such as real-time traffic conditions and new requests. This research proposes a heuristic approach to resolve on-line issues, such as real-time travel cost and real-time requests. In the heuristic approach, the Petals method is deployed to build the initial route for commercial vehicle, and the Tabu Search is used to update routes. In order to consider possible new requests, a rolling-horizon approach is implemented to react to real situations. Numerical experiments based on DynaTAIWAN are conducted for a test network and a real network－ Tainan City network to illustrate the proposed algorithm.

碩士<br>國立東華大學<br>運籌管理研究所<br>106<br>The statistics from the Ministry of Transportation and Communications shows that self-owned cars and motorcycles are the main means of transportation in Taiwan. However, on average a car owner only uses his car for eight hours per week, i.e., while cars are on demand, most of the time they are idling. Thus, if there is a Short-Term Vehicle Rental Service, then there is no need for citizens to buy cars, which can save citizens much money on buying and maintaining cars. The Short-Term Vehicle Rental Service comes from the Carsharing concept. Many signals show that Carsharing will be the reality in the near future. This thesis discusses how to solve the vehicle imbalanced problem for one-way can rental for the Short-Term Vehicle Rental Service, ideally for self-driving vehicles. For one-way car rental, a customer can rent a car from one place and return it to another place. Also, for Short-Term Vehicle Rental Service, the car rental duration of customers can be measured in hour or even in minute. As cars are moved by customers to various places, the distribution of cars at rental spots may not match with the actual demand of cars. It is necessary to allocate and relocate cars to balance the supply and demand of cars so that customers can have cars to use. This thesis proposes four allocation and relocation methods (FIFO, RFIFO, MINRE, and RMINRE) to solve the problem. The profit and various types of cost of these methods are compared to those of the NMORE method, the naïve scheme that allocates but does not relocate cars. The results show that all four proposed allocation and relocation methods are better than NMORE. Among the four proposed methods, MINRE provides the best performance in relocation cost, total cost, and total profit.

Doctoral Degree in Industrial and Systems Engineering<br>The real time management paradigm implies real-time decision making and enable dynamic reconfiguration of enterprises. In some areas it is possible to find a number of real time management applications, while in manufacturing systems the real time management is still in initial research state. Also, there is a lack of research of scheduling problems considering larger size manufacturing systems. This project aims to validate the following hypotheses: (1) real time management paradigm is more suitable for production scheduling in ubiquitous production networks under conditions of dynamic environments than the fixed horizon and rolling horizon paradigms, and (2) Real time management paradigm contributes to economic and environmental sustainability. The validation was based on simulation, through secondary data collection, which was the base for conduction of all simulations for the validation process. It were investigated four scenarios for validation. The first case represented the case with secondary data (from literature), considering 8 jobs and 8 machines. The second case represented the case with data secondary data with variations, considering 150 jobs and 8 machines. The third case represented the case with data secondary data with variations, considering 180 jobs and 64 machines. The forth case represented the hybrid case of 8 jobs and 64 machines and 8 jobs and 200 machines. A kind of greedy algorithm was considered for the resources (machines) selection, i.e. for each resource selection the choice of the best resource is made at that time, not looking for forward solutions. The validation was carried out by two instruments for hypotheses validation, the original environment model and the original simulator developed. The results obtained for the described scenarios validates the hypotheses that the real time management scheduling paradigm is more suitable when compared with other production scheduling paradigms, and that the real time management contributes to the economic and environmental sustainability. This research contributed to the phenomenology of real time management in ubiquitous and cloud manufacturing systems under conditions of dynamic environments. Further, future work is considered to create new research projects under this topic.<br>O paradigma de gestão em tempo real implica a tomada de decisão em tempo real e permite a reconfiguração dinâmica das empresas. Em algumas áreas é possível encontrar um número de aplicações da gestão em tempo real, enquanto nos sistemas de produção a gestão em tempo real ainda se encontra numa fase inicial de investigação. Existe ainda um falta de investigação nos problemas de escalonamento considerando sistemas de produção de tamanhos grandes. Este projeto tem como objetivo a validação das seguintes hipóteses: (1) o paradigma de gestão em tempo real é mais adequado para sistemas de produção em redes de produção ubíquas em condições de ambientes dinâmicos do que os paradigmas de horizonte fixo e horizonte rolante, e (2) o paradigma de gestão em tempo real contribui para a sustentabilidade económica e ambiental. A validação foi baseada em simulação, através da recolha de dados secundários, que serviram de base para condução de todas as simulações para o processo de validação. Para a validação foram investigados quatro senários: o caso com dados secundários (da literatura), considerando 8 jobs e 8 máquinas, o caso com dados secundários com variações, considerando 150 jobs e 64 máquinas, o caso com dados secundários com variações, considerando 180 jobs e 64 máquinas, e um caso hibrido considerando 8 jobs e 64 máquinas e 8 jobs e 200 máquinas. Um tipo de algoritmo guloso foi considerado para a seleção de recursos (máquinas), isto é, para cada seleção de recursos, a escola do melhor recurso é feita nesse momento, não olhando para soluções futuras. A validação foi realizada através de dois instrumentos para a validação de hipóteses, um modelo de ambiente original e um simulador original desenvolvido. Os resultados obtidos para os senários descritos validam as hipóteses de que o paradigma de gestão em tempo real é mais adequado quando comparado com outros paradigmas de escalonamento de produção, e que a gestão em tempo real contribui para a sustentabilidade económica e ambiental. Esta investigação contribuiu para a fenomenologia da gestão em tempo real em sistemas de produção ubíquos e cloud em condições de ambientes dinâmicos. Além disso, foi considerado trabalhos futuros para a criação de novos projetos de investigação sobre este tema.<br>The PhD project had financial support from the FCT – Fundação para a Ciência e a Tecnologia – under the Doctoral grant number SFRH/BD/85672/2012.

Cette thèse étudie le problème du routage des locomotives qui se pose à la Compagnie des chemins de fer nationaux du Canada (CN) - le plus grand chemin de fer au Canada en termes de revenus et de taille physique de son réseau ferroviaire. Le problème vise à déterminer la séquence des activités de chaque locomotive sur un horizon de planification donné. Dans ce contexte, il faut prendre des décisions liées à l'affectation de locomotives aux trains planifiés en tenant compte des besoins d'entretien des locomotives. D’autres décisions traitant l'envoi de locomotives aux gares par mouvements à vide, les déplacements légers (sans tirer des wagons) et la location de locomotives tierces doivent également être prises en compte. Sur la base d'une formulation de programmation en nombres entiers et d'un réseau espace-temps présentés dans la littérature, nous introduisons une approche par horizon roulant pour trouver des solutions sous-optimales de ce problème dans un temps de calcul acceptable. Une formulation mathématique et un réseau espace-temps issus de la littérature sont adaptés à notre problème. Nous introduisons un nouveau type d'arcs pour le réseau et de nouvelles contraintes pour le modèle pour faire face aux problèmes qui se posent lors de la division de l'horizon de planification en plus petits morceaux. Les expériences numériques sur des instances réelles montrent les avantages et les inconvénients de notre algorithme par rapport à une approche exacte.<br>This thesis addresses the locomotive routing problem arising at the Canadian National Railway Company (CN) - the largest railway in Canada in terms of both revenue and the physical size of its rail network. The problem aims to determine the sequence of activities for each locomotive over the planning horizon. Besides assigning locomotives to scheduled trains and considering scheduled locomotive maintenance requirements, the problem also includes other decisions, such as sending locomotives to stations by deadheading, light traveling, and leasing of third-party locomotives. Based on an Integer Programming formulation and a Time-Expanded Network presented in the literature, we introduce a Rolling Horizon Approach (RHA) as a method to find near-optimal solutions of this problem in acceptable computing time. We adapt a mathematical formulation and a space-time network from the literature. We introduce a new type of arcs for the network and new constraints for the model to cope with issues arising when dividing the planning horizon into smaller ones. Computational experiments on real-life instances show the pros and cons of our algorithm when compared to an exact solution approach.

Bicycle sharing systems (BSS) have emerged as a powerful stimulus to non- motorized travel, especially for short-distance trips. However, the imbalances in the distribution of bicycles in BSS are widely observed. It is thus necessary to reposition bicycles to reduce the unmet demand due to such imbalances as much as possible. This paper formulates a new mixed-integer linear programming model considering the dynamic nature of the demand to solve the repositioning problem, which is later validated by an illustrative example. Due to the NP-Hard nature of this problem, we seek for two heuristics (greedy algorithm and rolling horizon approach) and one exact solution method (Benders’ decomposition) to get an acceptable solution for problems with large instances within a reasonable computation time. We create four datasets based on real world data with 12, 24, 36, and 48 stations respectively. Computational results show that our model and solution methods performed well. Finally, this paper gives some suggestions on extensions or modifications that might be added to our work in the future.<br>text

Thesis (M.S.)--University of Wisconsin--Madison, 2000.<br>Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 64-68).

碩士<br>淡江大學<br>資訊管理學系碩士班<br>97<br>This study integrates the bidding decision and production planning based on the concept of advanced available-to-promise (AATP) inventory with a rolling planning horizon. Customer requests arrive in a random fashion, and bidding decisions are made for a batch of requests collected over a batching interval. This decision process repeated for every specified batching interval, and the current decision-making must take into account the previously committed orders in earlier phases. The problem is formulated as a mixed integer programming model with fuzzy constraints, which express the decision-maker’s subjective judgment regarding customer’s price tolerance. The proposed model embeds the AATP concept to support accurate computation of profit and customer order promising. A genetic algorithm is developed to solve the problem. Performance of the proposed approach is evaluated through experiments conducted by computer simulation.

Dissertação de mestrado integrado em Engenharia e Gestão Industrial<br>Hoje em dia tem-se a perceção do crescimento das empresas como um fator importante no desenvolvimento da economia. Como tal, Associações e Projetos têm vindo a desenvolver projetos traçados para o que as empresas necessitam, apontando para a crescente aposta em sistemas de gestão em tempo real. Nesse sentido nesta dissertação é proposta a investigação sobre o desenvolvimento de um modelo de gestão em tempo real para empresas virtuais (empresas em rede), com vista a redução do tempo de resposta ao mercado. Além deste modelo, e devido à importância do tempo de reconfiguração na crescente necessidade de alinhamento de negócio das empresas, desenvolveu-se uma estrutura para o tempo de reconfiguração e integração, onde se melhorou o modelo de estrutura do tempo de integração, introduzindo o tempo de transporte entre recursos. Com a construção e a validação do modelo de gestão em tempo real verificou-se a necessidade das empresas conseguirem mudar de recursos quase em tempo real, a cada momento de reconfiguração. No contexto de rede de empresas, estas devem ser essencialmente pequenas empresas devido aos seus baixos custos fixos. A dissertação apresenta contribuição original para a literatura através (1) do desenvolvimento de um modelo de gestão em tempo real onde o processo de gestão em tempo real é realizado através de um modelo teórico, e (2) do desenvolvimento de uma estrutura para o tempo de integração através da construção e preenchimento de novas visões sobre as arquiteturas de integração. Desta dissertação surge ainda a necessidade de trabalho futuro em campo empresarial que certamente irá trazer uma mais-valia para as empresas em rede, com o objetivo de as tornar mais cooperantes entre si, de modo a satisfazer objetivamente os seus clientes e reduzir o consumo de energia, como por exemplo, nos serviços de transporte.<br>The growth of enterprises is seen as a relevant economic development factor in nowadays. Aligning with the contemporary and emergent enterprises needs, the main company‘s investments and projects focus goes towards the real time management systems. Considering this and in order to make more agile and to minimize the time-to-market reaction, the development of a new model of real time management on virtual enterprises is proposed in the adjacent work of this thesis. The emergent need to be quickly aligned with the continuous changes on global business paradigms and overcome the competition brought by the multiple potential stakeholders, the time to reconfigure and to face with the new requirements is critical. Since a new structure for reconfiguration and integration times that considers the transport time between resources was developed and a better integration time structured was archived. After the proposed real time management model validation, the enterprises needs for real time resources change in their reconfiguration process, became evident. Furthermore, in a networked enterprises context these companies need to be essentially small enterprises due to their lower fixed costs. This thesis presents an innovative scientific contribution to real time systems since it follows a theoretical model. It develops an integration time structure through the construction and fulfilment of new visions about integration architectures, as well. From this thesis appears the need of future work in the industry that will bring an added value to the networked enterprise, in order to make them more co-operative to achieve the client‘s needs and reduce energy consumption.

[ES] Con la globalización de los mercados y el aumento de la competitividad, la coordinación se ha convertido en un punto estratégico en la gestión de la cadena de suministro. De hecho, cada actor de la cadena de suministro ya no debe tomar decisiones sin considerar todos los eslabones, sean proveedores, proveedores de proveedores o clientes y estos internos o externos a la organización. Las cadenas de suministro son cada vez más complejas y distribuidas, compuestas por múltiples organizaciones con diferentes objetivos y políticas. La coordinación se puede lograr utilizando uno de estos dos enfoques para la toma de decisiones coordinadas: centralizada o descentralizada con un mecanismo de coordinación. Pero, las empresas son reacias a compartir información, ya sea por la confidencialidad de los datos o porque los modelos centralizados resultantes son de gran complejidad que dificultan su manejo y actualización. Además, aquellas empresas que buscan tomar decisiones en tiempo real requieren de modelos ligeros y ágiles, que, con toda la información local y coordinada con el resto, permitan tomar decisiones rápidas. Las empresas interesadas en la coordinación descentralizada con un mecanismo de coordinación esperan obtener mejores resultados con respecto a la no coordinación, aunque deberían asumir tener peores resultados que con la coordinación centralizada. Para ello en esta tesis, se han estudiado los distintos mecanismos de coordinación para la toma de decisiones descentralizada, dentro de un entorno del procedimiento de horizontes rodantes y con herramienta de planificación y programación de las operaciones basada en el concepto de stroke, que extiende el concepto de lista de materiales más allá de las estructuras tradicionales. Estos permiten desarrollar la formulación de la programación matemática y los mecanismos de coordinación necesarios para resolver los problemas de planificación de operaciones. Esta tesis se presenta como una secuencia de capítulos, con el objeto de analizar y presentar la propuesta de mecanismo de coordinación distribuido con unos recursos compartidos. Los distintos capítulos han servido de base para la preparación de artículos científicos. Estos artículos han sido presentados en congresos de la materia y remitidos a revistas científicas.<br>[CAT] Amb la globalització dels mercats i l'augment de la competitivitat, la coordinació s'ha convertit en un punt estratègic en la gestió de la cadena de subministrament. De fet, cada actor de la cadena de subministrament ja no ha de prendre decisions sense considerar totes les baules, siguen proveïdors, sub-proveïdors o clients i aquests interns o externs a l'organització. Les cadenes de subministrament són cada vegada més complexes i distribuïdes, compostes per múltiples organitzacions amb diferents objectius i polítiques. La coordinació es pot aconseguir utilitzant un d'aquests dos enfocaments per a la presa de decisions coordinades: centralitzat o descentralitzat amb un mecanisme de coordinació. Però, les empreses són poc inclinades a compartir informació, ja siga per la confidencialitat de les dades o perquè els models centralitzats resultants són de gran complexitat que dificulten el seu maneig i actualització. A més, aquelles empresa que busquen prendre decisions en temps real requereixen de models lleugers i àgils, que, amb tota la informació local i coordinada amb la resta, permeten prendre decisions ràpides. Les empreses interessades en la coordinació descentralitzada amb un mecanisme de coordinació esperen obtindre millors resultats respecte de la no coordinació encara que haurien d'assumir tindre pitjors resultats que amb la coordinació centralitzada. Per a això en aquesta tesi, s'han estudiat els diferents mecanismes de coordinació per a la presa de decisions descentralitzada, dins d'un entorn d'horitzons rodant i amb eines de planificació i programació de les operacions basada en el concepte de stroke, que estén el concepte de llista de materials més enllà de les estructures tradicionals. Aquests permeten desenvolupar la formulació de la programació matemàtica i els mecanismes de coordinació necessaris per a resoldre els problemes de planificació d'operacions. Aquesta tesi es presenta com una seqüència de capítols, a fi d'analitzar i presentar la proposta de mecanisme de coordinació distribuït amb uns recursos compartits. Els diferents capítols han servit de base per a la preparació d'articles científics. Aquests articles han sigut presentats en congressos de la matèria i remesos a revistes científiques.<br>[EN] With the globalization of markets and the increase of competitiveness, coordination has become a strategic point in the management of the supply chain. In fact, each actor in the supply chain must no longer make decisions without considering all the links, whether suppliers, sub-suppliers or customers and those internal or external to the organization. Supply chains are increasingly complex and distributed, composed of multiple organizations with different objectives and policies. Coordination can be achieved using one of these two approaches to coordinate decision making: centralized or decentralized with a coordination mechanism. However, companies are reluctant to share information, either because of the confidentiality of the data or because the resulting centralized models are of great complexity that make their management and update them. In addition, those companies that seek to make decisions in real time require lightweight and agile models, which, with all the local information and coordinated with the rest, allow quick decisions. Companies interested in decentralized coordination with a coordination mechanism expect to obtain better results regarding non-coordination although they should assume to have worse results than with centralized coordination. To this end, in this thesis, the different coordination mechanisms for decentralized decision making have been studied, within an environment of rolling horizons and with tools for planning and scheduling operations based on the concept of stroke, which extends the concept of list of materials beyond traditional structures. These allow to develop the formulation of the mathematical programming and the coordination mechanisms necessary to solve the operations planning problems. This thesis is presented as a sequence of chapters, in order to analyse and present the proposal of distributed coordination mechanism with shared resources. The different chapters have served as the basis for the preparation of scientific articles. These articles have been presented at congresses of the subject and submitted to scientific journals.<br>Rius Sorolla, GV. (2019). Modelos y Algoritmos de Coordinación para la Planificación de Operaciones basadas en el concepto Stroke en Redes de Suministro distribuidas y con alternativas [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/134017<br>TESIS

<p>Forest management involves numerous stochastic elements. To sustainably manage forest resources, it is crucial to acknowledge these sources as uncertainty or risk, and incorporate them in adaptive decision-making. Here, I developed several stochastic programming models in the form of passive or active adaptive management for natural mixed-species hardwood forests in Indiana. I demonstrated how to use these tools to deal with time-invariant and time-variant natural disturbances in optimal planning of harvests.</p> <p> Markov decision process (MDP) models were first constructed based upon stochastic simulations of an empirical forest growth model for the forest type of interest. Then, they were optimized to seek the optimal or near-optimal harvesting decisions while considering risk and uncertainty in natural disturbances. In particular, a classic expected-criterion infinite-horizon MDP model was first used as a passive adaptive management tool to determine the optimal action for a specific forest state when the probabilities of forest transition remained constant over time. Next, a two-stage non-stationary MDP model combined with a rolling-horizon heuristic was developed, which allowed information update and then adjustments of decisions accordingly. It was used to determine active adaptive harvesting decisions for a three-decade planning horizon during which natural disturbance probabilities may be altered by climate change.</p> <p> The empirical results can be used to make some useful quantitative management recommendations, and shed light on the impacts of decision-making on the forests and timber yield when some stochastic elements in forest management changed. In general, the increase in the likelihood of damages by natural disturbance to forests would cause more aggressive decisions if timber production was the management objective. When windthrow did not pose a threat to mixed hardwood forests, the average optimal yield of sawtimber was estimated to be 1,376 ft³/ac/acre, while the residual basal area was 88 ft²/ac. Assuming a 10 percent per decade probability of windthrow that would reduce the stand basal area considerably, the optimal sawtimber yield per decade would decline by 17%, but the residual basal area would be lowered only by 5%. Assuming that the frequency of windthrow increased in the magnitude of 5% every decade under climate change, the average sawtimber yield would be reduced by 31%, with an average residual basal area slightly around 76 ft²/ac. For validation purpose, I compared the total sawtimber yield in three decades obtained from the heuristic approach to that of a three-decade MDP model making <i>ex post</i> decisions. The heuristic approach was proved to provide a satisfactory result which was only about 18% lower than the actual optimum.</p> These findings highlight the need for landowners, both private and public, to monitor forests frequently and use flexible planning approaches in order to anticipate for climate change impacts. They also suggest that climate change may considerably lower sawtimber yield, causing a concerning decline in the timber supply in Indiana. Future improvements of the approaches used here are recommended, including addressing the changing stumpage market condition and developing a more flexible rolling-horizon heuristic approach.