• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 18
  • 10
  • 3
  • 2
  • 2
  • Tagged with
  • 40
  • 40
  • 18
  • 18
  • 13
  • 12
  • 12
  • 10
  • 10
  • 8
  • 8
  • 6
  • 6
  • 6
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Gestion supervisée de systèmes étendus à retards variables : cas des réseaux hydrographiques / Supervisory control of large scale system with varying time delay : hydrophical network case study

Nouasse, Houda 04 March 2015 (has links)
De part et d’autre de la Terre, on observe de plus en plus de phénomènes naturels dévastateurs, parmi lesquels les inondations constituent l’une des catastrophes les plus fréquentes. Ces dernières décennies d’importantes inondations ont été induites par les crues de rivières. Ces crues, dues à des pluies excessives ou aux eaux de ruissellement, causent sans cesse des pertes de vies humaines et des dégâts matériels importants. Pour remédier à ces problèmes, les réseaux hydrographiques sont de plus en plus équipés de moyens de détection de crues. Un facteur essentiel à la gestion de tels phénomènes est la réactivité. En effet, les gestionnaires des réseaux hydrographiques, dans ce genre de situation, doivent prendre rapidement des décisions importantes dans un contexte incertain, car la plupart de ces crues sont le fruit de phénomènes climatiques brusques, dont l’ampleur est difficile à évaluer avec précision. Nous proposons, dans ce mémoire, une méthode de gestion des crues dans des réseaux hydrographiques équipés de zones inondables contrôlées par des portes gravitationnelles. Dans un premier temps, nous avons modélisé notre méthode de gestion à l’aide d’un réseau de transport statique. Dans un second temps, nous l’avons enrichi en utilisant les réseaux de transport à retards dans le but de prendre en compte les temps de déplacement de la ressource gérée. Afin de pallier le problème de la taille importante des réseaux de transport à retards, nous avons élaboré un mécanisme de substitution combinant un réseau de transport statique réduit et une matrice de temporisation. De plus, ce mécanisme autorise la prise en compte des temps de transfert variables dépendant des débits, sans modification ni du réseau de transport, ni de la structure de la matrice de temporisation. Ce mécanisme permet donc une gestion simplifiée des temps de transferts, variables ou non. Avec ce mécanisme, l’évaluation du flot maximal à coût minimum, nous a permis, suivant les stratégies de gestion considérées, de consigner l’ouverture des portes des zones inondables afin d’écrêter la crue mais aussi afin de restituer cette eau stockée au moment opportun. Finalement, afin d’évaluer les apports de cette gestion, la méthode a été appliquée sur un cas d’étude basée sur un tronçon de rivière équipé de trois zones inondables et modélisé à l’aide de simulateurs hydrauliques combinant les approches de modélisation 1D et 2D. Les résultats de simulation obtenus ont montré que l’approche proposée permettait de réduire de manière significative les inondations en aval des cours d’eau. / On either side of the Earth, we observe more and more devastating natural phenomena. Amon these phenomena, floods are one of the most frequent and devastating natural disasters. During these last decades extensive flooding were caused by the flood of rivers. These floods due to excessive rainfall or runoff induce invariably the loss of human lives and material damages. To overcome these problems, water systems are increasingly equipped with means for detecting floods. A key factor in the management of such phenomena is responsiveness. Indeed, managers of river systems, faced to this kind of situation should quickly take important decisions in an uncertain context, as most of these floods are induced by abrupt climate events, whose magnitude is difficult to assess accuracy. We propose in this dissertation, a method of flood management in river systems equipped with flood zones controlled by gravitational gates. At first, we modeled our management method using a static transportation network. In a second step, we enriched it by using transportation networks with delays in order to take into account the travel time of the managed resource. The main difficulty of transportation networks with delays is their oversize. To overcome this problem, we developed an alternative mechanism combining a static reduced transportation network with a temporization matrix. Furthermore, this mechanism allows the consideration of variable time transfer depending on flows, without modification either on the transportation network, or on the structure of the temporization matrix. This mechanism allows simplified management of the transfer times, variable or not. With this mechanism, the evaluation of the minimum cost maximum flow allowed us, according to the management strategies considered, to compute the gate opening for floodplains in order to mitigate the flood but also to restore the water stored at the relevant time. Finally, to evaluate the contributions of this management, the method was applied to a case study based on a section of river equipped with three flood control reservoirs areas modeled using hydraulic simulators combining 1D and 2D models. The simulation results showed that the proposed approach allowed reducing significantly the floods downstream watercourses.
12

Modeling Cascading Network Disruptions under Uncertainty For Managing Hurricane Evacuation

January 2020 (has links)
abstract: Short-notice disasters such as hurricanes involve uncertainties in many facets, from the time of its occurrence to its impacts’ magnitude. Failure to incorporate these uncertainties can affect the effectiveness of the emergency responses. In the case of a hurricane event, uncertainties and corresponding impacts during a storm event can quickly cascade. Over the past decades, various storm forecast models have been developed to predict the storm uncertainties; however, access to the usage of these models is limited. Hence, as the first part of this research, a data-driven simulation model is developed with aim to generate spatial-temporal storm predicted hazards for each possible hurricane track modeled. The simulation model identifies a means to represent uncertainty in storm’s movement and its associated potential hazards in the form of probabilistic scenarios tree where each branch is associated with scenario-level storm track and weather profile. Storm hazards, such as strong winds, torrential rain, and storm surges, can inflict significant damage on the road network and affect the population’s ability to move during the storm event. A cascading network failure algorithm is introduced in the second part of the research. The algorithm takes the scenario-level storm hazards to predict uncertainties in mobility states over the storm event. In the third part of the research, a methodology is proposed to generate a sequence of actions that simultaneously solve the evacuation flow scheduling and suggested routes which minimize the total flow time, or the makespan, for the evacuation process from origins to destinations in the resulting stochastic time-dependent network. The methodology is implemented for the 2017 Hurricane Irma case study to recommend an evacuation policy for Manatee County, FL. The results are compared with evacuation plans for assumed scenarios; the research suggests that evacuation recommendations that are based on single scenarios reduce the effectiveness of the evacuation procedure. The overall contributions of the research presented here are new methodologies to: (1) predict and visualize the spatial-temporal impacts of an oncoming storm event, (2) predict uncertainties in the impacts to transportation infrastructure and mobility, and (3) determine the quickest evacuation schedule and routes under the uncertainties within the resulting stochastic transportation networks. / Dissertation/Thesis / Doctoral Dissertation Industrial Engineering 2020
13

Models and algorithms for fleet management of autonomous vehicles / Modèles et algorithmes de gestion de flottes de véhicules autonomes

Bsaybes, Sahar 26 October 2017 (has links)
Résumé indisponible. / The VIPAFLEET project aims at developing a framework to manage a fleet of IndividualPublic Autonomous Vehicles (VIPA). We consider a fleet of cars distributed at specifiedstations in an industrial area to supply internal transportation, where the cars can beused in different modes of circulation (tram mode, elevator mode, taxi mode). The goalis to develop and implement suitable algorithms for each mode in order to satisfy all therequests either under an economic point aspect or under a quality of service aspect, thisby varying the studied objective functions.We model the underlying online transportation system as a discrete event basedsystem and propose a corresponding fleet management framework, to handle modes,demands and commands. We consider three modes of circulation, tram, elevator andtaxi mode. We propose for each mode appropriate online algorithms and evaluate theirperformance, both in terms of competitive analysis and practical behavior by computationalresults. We treat in this work, the pickup and delivery problem related to theTram mode and the Elevator mode the pickup and delivery problem with time windowsrelated to the taxi mode by means of flows in time-expanded networks.
14

Optimal Evacuation Plans for Network Flows over Time Considering Congestion

Chamberlayne, Edward Pye 24 June 2011 (has links)
This dissertation seeks to advance the modeling of network flows over time for the purposes of improving evacuation planning. The devastation created by Hurricanes Katrina and Rita along the Gulf Coast of the United States in 2005 have recently emphasized the need to improve evacuation modeling and planning. The lessons learned from these events, and similar past emergencies, have highlighted the problem of congestion on the interstate and freeways during an evacuation. The intent of this research is to develop evacuation demand management strategies that can reduce congestion, delay, and ultimately save lives during regional evacuations. The primary focus of this research will concern short-notice evacuations, such as hurricane evacuations, conducted by automobiles. Additionally, this dissertation addresses some traffic flow and optimization deficiencies concerning the modeling of congested network flows. This dissertation is a compilation of three manuscripts. Chapters 3 and 4 examine modeling network flows over time with congestion. Chapter 3 demonstrates the effects of congestion on flows using a microscopic traffic simulation software package, INTEGRATION. The flow reductions from the simulation are consistent with those found in several empirical studies. The simulation allows for the examination of the various contributing factors to the flow reductions caused by congestion, including level of demand, roadway geometry and capacity, vehicle dynamics, traffic stream composition, and lane changing behavior. Chapter 4 addresses some of the modeling and implementation issues encountered in evacuation planning and presents an improved modeling framework that reduces network flows due to congestion. The framework uses a cell-based linear traffic flow model within a mixed integer linear program (MILP) to model network flows over time in order to produce sets of decisions for use within an evacuation plan. The traffic flow model is an improvement based upon the Cell Transmission Model (CTM) introduced in Daganzo (1994) and Daganzo (1995) by reducing network flows due to congestion. The flow reductions are calibrated according to the traffic simulation studies conducted in Chapter 3. The MILP is based upon the linear program developed in Ziliaskopoulos (2000); however, it eliminates the "traffic holding" phenomenon where it cannot be implemented realistically within a transportation network. This phenomenon is commonly found in mathematical programs used for dynamic traffic assignment where the traffic is unrealistically held back in order to determine an optimum solution. Lastly, we propose additional constraints for the MILP that improve the computational performance by over 90%. These constraints exploit the relation of the binary variables based on the network topology. Chapter 5 applies the improved modeling framework developed in Chapter 4 to implement a demand management strategy called group-level staging -- the practice of evacuating different groups of evacuees at different times in order to reduce the evacuation duration. This chapter evaluates the benefits of group-level staging, as compared to the current practice of simultaneous evacuation, and explores the behavior of the modeling framework under various objective functions. / Ph. D.
15

Otimização de medidas de gerenciamento de fluxo de tráfego aéreo para múltiplos elementos regulados. / Optimization of air traffic management measures for multiple regulated elements.

Koroishi, Giovanna Ono 02 May 2019 (has links)
O Serviço de Gerenciamento de Fluxo de Tráfego Aéreo (ATFM) estabelece um controle de fluxo seguro, ordenado e eficiente de acordo com a capacidade da infraestrutura e dos serviços de controle. O Gerenciamento ´e realizado com o auxílio de sistemas automatizados. Tais sistemas implementam programas que ajustam a demanda de voos à capacidade do espaço aéreo. Algoritmos simples podem sugerir medidas ATFM para solucionar a saturação em um conjunto restrito de elementos regulados (aeródromos, regiões do espaço aéreo, fixos ou aerovias). A natureza interconectada dos elementos regulados, que compõem o fluxo de tráfego aéreo, demanda uma abordagem mais abrangente para atingir o uso ótimo desses recursos, uma vez que outros problemas podem surgir quando a otimização local é aplicada a um elemento sem levar em conta seus elementos relacionados. Nem sempre há a necessidade do planejamento estratégico ser um ótimo global, uma vez que cenários viáveis e sub-ótimos encontrados com menor custo computacional podem representar soluções satisfatórias. O aumento da demanda do tráfego aéreo, no entanto, tem fomentado a aplicação de programas de geração de medidas ATFM mais complexos. Esta pesquisa implementou um programa de otimização global para a geração de medidas ATFM em cenários de larga escala do mundo real. O problema ´e modelado como um problema de programa¸c~ao inteira e o modelo adotado ´e abrangente, pois prevê atraso em solo, em voo, alteração de velocidade e rerroteamento. O programa é capaz de balancear o fluxo atendendo restrições de capacidade dos aeródromos e dos setores. Além disso, foi desenvolvida uma interface de visualização e edição de dados para os cenários estudados. Dados de voos no espaço aéreo brasileiro foram processados e utilizados para testar a solução implementada e mostraram a viabilidade do método. A utilização de um programa de otimização que leva em conta mais restrições potencialmente irá contribuir com o aumento de eficiência no uso da infraestrutura e do espaço aéreo de forma segura. / The Air Traffic Flow Management Service (ATFM) establishes a secure, orderly and efficient flow control according to the capacity of the infrastructure and control services. The Management is performed with the aid of automated systems. Such systems implement programs that adjust the flight demand to the airspace capacity. Simple algorithms might suggest ATFM measures to resolve saturation in a restricted set of regulated elements (aerodromes, airspace regions, fixes or airways). The interconnected nature of the regulated elements that make up the air traffic flow requires a more comprehensive approach to achieve optimum use of these resources, since other problems can arise when local optimization is applied to an element without regard to its related elements. There is not always a need for strategic planning to be a global optimum, since feasible and sub-optimal scenarios encountered at lower computational cost might represent satisfactory solutions. The increase in air traffic demand, however, has encouraged the application of programs to generate more complex ATFM measures. This research implemented a global optimization program for the generation of ATFM measures in large-scale real-world scenarios. The problem is modeled as an integer programming problem and the adopted model is comprehensive, since it provides ground and airborne delays, change of speed and re-routing. The program is able to balance the flow by meeting capacity constraints of the aerodromes and sectors. In addition, a visualization and data editing interface was developed for the studied scenarios. Flight data in Brazilian airspace were processed and used to test the implemented solution and the viability of the method was shown. The use of an optimization program that takes into account more constraints will potentially contribute to increase the efficiency in use of infrastructure and airspace in a secure manner.
16

[en] MODELS AND ALGORITHMS FOR CONGESTION ANALYSIS AND YARD USE DETERMINATION IN RAILWAY LOGISTICS / [pt] MODELOS E ALGORITMOS PARA ANÁLISE DE CONGESTIONAMENTO E DETERMINAÇÃO DE PARADAS NA LOGÍSTICA FERROVIÁRIA

RAFAEL MARTINELLI PINTO 04 December 2007 (has links)
[pt] A importância do planejamento em logística ferroviária cresce a cada dia devido ao alto custo dos investimentos para o aumento da sua capacidade. Entretanto, planejar é uma atividade que exige uma representação suficientemente precisa da realidade estudada. Neste contexto, os modelos de programação matemática apresentam-se cada vez mais adequados. Isto decorre dos recentes avanços nos algoritmos e computadores disponíveis para sua resolução. Esta dissertação apresenta modelos e algoritmos para o planejamento ferroviário tático e estratégico, isto é feito estudando o Problema de Planejamento de Atendimento (PPA). Primeiramente este problema é considerado assumindo que toda a estrutura ferroviária está definida: a malha, a tração e os vagões disponíveis, os pátios para carga, descarga e transbordo, suas respectivas taxas de carga e descarga e as demandas previstas. Em seguida, a questão adicional de determinar os pátios onde paradas podem ser efetuadas é considerada. Finalmente, em uma terceira etapa, introduz-se a capacidade de se analisar os efeitos do congestionamento de trechos da malha e seu impacto nos tempos de circulação e na capacidade da estrutura logística. Modelos são apresentados para cada um dos níveis de complexidade do PPA. Algoritmos exatos e heurísticos e técnicas de pré- processamento, foram desenvolvidos para os tratamentos dos casos obtidos. Em todos os casos, foi possível resolver de maneira ótima ou quase ótima em tempo razoável, tanto em termos acadêmicos, como para a utilização prática. Resultados computacionais sobre um amplo conjunto de instâncias reais são apresentados. / [en] Planning in Railway Logistic is an activity with growing importance. This is due to the high costs of investment to increase the railway capacity. Nevertheless, planning in this context is a cumbersome task, since a precise representation is necessary to consider most relevant points in this activity. Mathematical programming is becoming one of the best ways derive precise representations and to solve them. This is due to the recent advances on algorithms and computers used in the resolution of mathematical programming problems. This dissertation presents models and algorithms for tactical and strategical railway planning what is done by studying a demand planning problem (PPA). First, this problem is considered assuming that all the railway structure is defined: the network, the locomotives and wagons available, the yards for loading and unloading with their respective rates, and the forecast of demands. Next, the question of deciding the yards to stop is considered. Finally, in a third step, the effect of congestion in parts of the network is introduced to the models. This allows analyzing the variation in the travel times and its consequence in the logistic structure capacity. Models are presented for all cases of the PPA. Exact and heuristic algorithms, as well as pre-processing techniques, are described for the problem resolution. In all cases, the resulting approach allowed to solve the problems optimally or quasioptimally in a reasonable computing time. Computational results are presented on a wide set of real world instances.
17

A viabilização de softwares comerciais na roteirização de veículos de serviços de entregas, visando a geração de respostas rápidas e eficientes / The feasibility of commercial software for vehicles routing of delivery services in order to obtain fast and efficient answers

Santos, Cely Martins dos 29 April 1999 (has links)
Este trabalho foi motivado pela necessidade de otimização nos serviços de entregas urbanas combinados com o alto custo de implantação e customização da maioria dos pacotes disponíveis comercialmente, que muitas empresas se defrontam, na expectativa de obtenção de respostas rápidas e eficientes, numa base diária. Geralmente a utilização destes software requerem grandes investimentos de tempo e recursos. Os custos operacionais do transporte de cargas têm experimentado um aumento expressivo devido a fatores que, de uma forma ou de outra, impedem o fluxo eficiente dos veículos na rede, tomando evidente a necessidade de ferramentas flexíveis e efetivas. Vários estudos encontrados na literatura revelaram que fatores como restrições de circulação e velocidades nos arcos têm contribuído para aumentar distâncias de percursos e a frota de veículos. Geralmente, estas rotas são planejadas de forma simplificada, utilizando um fator de correção, que fornece uma solução aproximada. Um SIG foi objeto de estudo na operação de entregas urbanas, de forma a atingir os objetivos deste trabalho. O estudo de caso abordou os serviços de entregas de bebidas na cidade de São Carlos, onde foi aplicada a heurística de economias de Clarke & Wright implementadas no software TransCAD 3.2. Foram feitas diversas simulações, comparando os resultados das distâncias em rede com os valores das distâncias estimadas, como também com as distâncias percorridas pela empresa distribuidora. / This research was motivated by the necessity of optimization of urban delivery services and the high cost of implementation and customization of most routing packages commercially available. Moreover, the companies expect to obtain fast and efficient answers on a daily base. The use of some routing software generally requires significant investments of time and other resources. The operational costs of freight transport have had a remarkable increase due to factors which somehow restraint the efficient flow of the vehicles in a network, leading to the need of flexible and effective tools. Several studies in the literature have revealed that factors such as restrictions of circulation and speed on network contribute to increase the travel distances and the fleet size. Generally, these routes are planned in a simplified way, using a correction factor to get an approximated solution. This research has considered the use of Geographical Information Systems as a tool to achieve better results for routing delivery services. The case study was the delivery service of beverages in the city of São Carlos. The Clarke & Wright\'s heuristic of economies was irnplemented in the TransCAD 3.2 software. Several simulations were carried out, comparing the results of route length, considering network and estimated distances, as well as the real one traveled by the delivery company\'s vehicles.
18

A viabilização de softwares comerciais na roteirização de veículos de serviços de entregas, visando a geração de respostas rápidas e eficientes / The feasibility of commercial software for vehicles routing of delivery services in order to obtain fast and efficient answers

Cely Martins dos Santos 29 April 1999 (has links)
Este trabalho foi motivado pela necessidade de otimização nos serviços de entregas urbanas combinados com o alto custo de implantação e customização da maioria dos pacotes disponíveis comercialmente, que muitas empresas se defrontam, na expectativa de obtenção de respostas rápidas e eficientes, numa base diária. Geralmente a utilização destes software requerem grandes investimentos de tempo e recursos. Os custos operacionais do transporte de cargas têm experimentado um aumento expressivo devido a fatores que, de uma forma ou de outra, impedem o fluxo eficiente dos veículos na rede, tomando evidente a necessidade de ferramentas flexíveis e efetivas. Vários estudos encontrados na literatura revelaram que fatores como restrições de circulação e velocidades nos arcos têm contribuído para aumentar distâncias de percursos e a frota de veículos. Geralmente, estas rotas são planejadas de forma simplificada, utilizando um fator de correção, que fornece uma solução aproximada. Um SIG foi objeto de estudo na operação de entregas urbanas, de forma a atingir os objetivos deste trabalho. O estudo de caso abordou os serviços de entregas de bebidas na cidade de São Carlos, onde foi aplicada a heurística de economias de Clarke & Wright implementadas no software TransCAD 3.2. Foram feitas diversas simulações, comparando os resultados das distâncias em rede com os valores das distâncias estimadas, como também com as distâncias percorridas pela empresa distribuidora. / This research was motivated by the necessity of optimization of urban delivery services and the high cost of implementation and customization of most routing packages commercially available. Moreover, the companies expect to obtain fast and efficient answers on a daily base. The use of some routing software generally requires significant investments of time and other resources. The operational costs of freight transport have had a remarkable increase due to factors which somehow restraint the efficient flow of the vehicles in a network, leading to the need of flexible and effective tools. Several studies in the literature have revealed that factors such as restrictions of circulation and speed on network contribute to increase the travel distances and the fleet size. Generally, these routes are planned in a simplified way, using a correction factor to get an approximated solution. This research has considered the use of Geographical Information Systems as a tool to achieve better results for routing delivery services. The case study was the delivery service of beverages in the city of São Carlos. The Clarke & Wright\'s heuristic of economies was irnplemented in the TransCAD 3.2 software. Several simulations were carried out, comparing the results of route length, considering network and estimated distances, as well as the real one traveled by the delivery company\'s vehicles.
19

A Bicriteria Rescheduling Problem On Unrelated Parallel Machines: Network Flow And Enumeration Based Approaches

Ozlen, Melih 01 November 2006 (has links) (PDF)
This study considers bicriteria approaches to the minimum cost network flow problem and a rescheduling problem where those approaches find their applications. For the bicriteria integer minimum cost network flow problem, we generate all efficient solutions in two phases. The first phase generates the extreme supported efficient points that are the extreme points of the objective space of the continuous bicriteria network flow problem. In the second phase, we generate the nonextreme supported and unsupported efficient points by Integer Programming Based approaches. Our rescheduling problem considers parallel unrelated machine environments. The criteria are the total flow time as an efficiency measure and the total reassignment cost as a stability measure. We show that the problems that address linear functions of the two criteria can be represented by bicriteria network flow models. To generate all efficient solutions, we use a Classical Approach that is based on the optimal solutions of the singly constrained network flow problem and provide a Branch and Bound approach that starts with extreme supported efficient set and uses powerful bounds. To find an optimal solution to any nonlinear function of the two criteria, we provide a Branch and Bound approach and an Integer Programming Based approach that eliminates some portions of the efficient set that cannot provide improved solutions. We contribute both to the network flow and scheduling literature by proposing algorithms to the bicriteria network flow models and applying them to a rescheduling problem that is bicriteria in nature. The results of our extensive computations with up to 100 jobs and 12 machines have revealed that, the Branch and Bound algorithm finds the efficient set in less computational effort compared to the classical approach. In minimizing a nonlinear function of the two criteria both IP Based approach and Branch and Bound algorithm perform quite satisfactory.
20

[en] TACTICAL LESS-THAN-TRUCKLOAD TRANSPORTATION PLANNING: MODELS AND ALGORITHMS / [pt] PLANEJAMENTO TÁTICO NO TRANSPORTE RODOVIÁRIO DE CARGAS FRACIONADAS: MODELOS E ALGORITMOS

PEDRO DE MOURA E CUNHA 10 October 2008 (has links)
[pt] Problemas de transporte de cargas fracionadas são grandes candidatos para a aplicação de técnicas de otimização como forma de obter um melhor aproveitamento de recursos. Nesta dissertação, são apresentados modelos de programação inteira e os algoritmos desenvolvidos para a resolução adequada dos problemas estudados neste contexto. O foco é o planejamento da movimentação dos veículos para o atendimento das demandas ao longo de um período pré-definido. Diferentes formas de contratação dos veículos são consideradas, demandas possuem janelas de tempo para serem atendidas e podem compartilhar um mesmo veículo em um ou mais trechos do seu caminho até o destino. Conexões são permitidas, ou seja, uma demanda pode utilizar mais de um veículo para o seu atendimento, respeitando as capacidades operacionais dos centros de distribuição e coleta. Os objetivos abrangem o dimensionamento da frota, que possui um custo fixo, e o planejamento da operação ao longo do período. Este deve determinar quais demandas são transportadas por quais veículos em que instantes e em que trechos. O método de resolução proposto utiliza algoritmos para a construção e pré-processamento de grafos que representam o problema e permitem que a formulação como programa inteiro tenha uma resolução mais efciente. Além disso, o algoritmo correspondente resolve uma sequência de programas inteiros para obter soluções viáveis de qualidade para as diferentes versões do problema aqui considerado. Melhorias nos limites inferiores obtidos também são propostas. O código resultante foi testado em um conjunto de instâncias baseadas na operação de uma transportadora brasileira de grande porte. Resultados foram obtidos tanto para condições de utilização reais, isto é, com o tempo de execução limitado, como para testar os limites do método proposto. Em ambos os casos pôde-se obter soluções de alta qualidade comprovada. / [en] Less-than-truckload transportation problems are great candidates for the application of optimization techniques as a form to obtain a better exploitation of resources. This thesis introduces integer programming models and the developed algorithms for the proper resolution of the studied problems in this context. The focal point is the vehicle's dislocation planning for the ideal attendance of the demands during a certain time period. Different forms of vehicle contract are considered. There are time windows for the attendances and demands can share a same vehicle in one or more parts of its route until his destination. Connections are allowed, that is, demands can use more than one vehicle for its attendance, respecting the operational capacities of the centers (collection and distribution stations). The goals embraces the sizing of the proper fleet which has a fixed cost, and the operation's planning during the period. This one should determine which demands are transported by which vehicles in what instants and where on routes. The resolution's method proposed uses algorithms for the graph's construction and pre-processing which represents the problem and allows that the formulation, as an integer program, to have a resolution more efficient. Furthermore, the corresponding algorithm solves a sequence of integer programs to obtain feasible quality solutions for the differents versions of the considered problem. Improvements on the lower bounds gotten are also proposed. The resulting code was tested in a set of proposed instances that were based on the operation of an important brazilian trucking company . Results were acquired such for conditions of real utilization, in other words, with a limited time of execution, as to test the limits of the proposed method. In both cases, solutions of comproved high quality were obtained.

Page generated in 0.0451 seconds