Academic literature 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.