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Meta-heurísticas para problemas integrados de roteamento e carregamento de veículos / Meta-heuristics for integrated vehicle routing and loading problemsSantini, Luigi Tavolaro 23 February 2017 (has links)
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Previous issue date: 2017-02-23 / The present work deals with the Capacitated Vehicle Routing Problem with Three-Dimensional Loading Constraints. This problem is difficult to solve exactly, still relatively little studied, but important in the logistics activities of movement, warehousing and transportation. This problem consists in minimizing the total traveled distance by a homogeneous fleet of vehicles that address the issue of deliveries of customer demands, in which these demands are composed of items that have three relevant spatial dimensions. The objective of the present work is to develop heuristic and metaheuristic algorithms to solve the problem in question. The algorithms are based on the Clarke & Wright and George & Robinson heuristics, and on the Iterated Local Search and Adaptive Large Neighborhood Search metaheuristics. In the proposed algorithm, the routing problem is firstly addressed by adapting the Clarke & Wright heuristic, creating routes that are used to verify the loading pattern, thus obtaining an initial solution. In the following, an extensive search in the solution neighborhood is applied with the Iterated Local Search metaheuristic. For the best results of this search, it is checked if the loading pattern is feasible using an adapted George & Robinson algorithm. If it is not feasible, the Adaptive Large Neighborhood Search metaheuristic is executed in an attempt to find a feasible solution to the loading problem. Instances from the literature are used to evaluate the efficiency of the developed methods. The results obtained for the routing problem individually were of paramount importance to ensure the effectiveness of the Iterated Local Search metaheuristic. For the loading problem individually, the tests were also satisfactory, allowing for several feasible loading patterns using the adapted George & Robinson algorithm and the Adaptive Large Neighborhood Search metaheuristic. The results obtained with the proposed algorithm for the integrated problem were also good, being very close to those in the literature and with computational time relatively lower. As perspectives for future research, it is intended to investigate more efficient ways of exploring the solution space of the integrated problem, as well as the use of other metaheuristics. / O presente trabalho trata do Problema de Roteamento de Veículos Capacitado com Restrições de Carregamento Tridimensional. Este é um problema de difícil solução exata, ainda relativamente pouco estudado, porém importante nas atividades logísticas de movimentação, armazenagem e transporte de produtos. Este problema consiste em minimizar a distância total percorrida por uma frota homogênea de veículos que supram a questão das entregas das demandas de clientes, em que tais demandas são compostas por itens que possuem três dimensões espaciais relevantes. O objetivo do presente trabalho consiste em desenvolver algoritmos heurísticos e meta-heurísticos para resolver o problema em questão. Os algoritmos são baseados nas heurísticas de Clarke & Wright e de George & Robinson, e nas meta-heurísticas Iterated Local Search e Adaptive Large Neighborhood Search. No algoritmo proposto, primeiro trata-se o problema de roteamento adaptando-se a heurística de Clarke & Wright, criando roteiros que são utilizados para a verificação do padrão de carregamento, tendo-se assim uma solução inicial. Em seguida, é aplicada uma busca extensiva na vizinhança com a meta-heurística Iterated Local Search. Para os melhores resultados desta busca, verifica-se se o padrão de carregamento é viável utilizando o algoritmo de George & Robinson adaptado. Nos casos em que não é viável, a meta-heurística Adaptive Large Neighborhood Search é executada na tentativa de se encontrar soluções viáveis para o problema de carregamento. Instâncias da literatura são utilizadas para avaliar a eficiência dos métodos desenvolvidos. Os resultados obtidos para o problema de roteamento separadamente foram de suma importância para assegurar a eficiência do meta-heurística Iterated Local Search. Para o problema de carregamento separadamente, os testes utilizando o algoritmo de George & Robinson adaptado e a meta-heurística Adaptive Large Neighborhood Search também foram satisfatórios, permitindo a obtenção de vários padrões de carregamento factíveis. Os resultados obtidos com o algoritmo proposto para o problema integrado também foram bons, sendo bastante próximos aos da literatura e com tempo computacional relativamente menor. Como perspectivas de pesquisas futuras, pretende-se estudar formas mais eficientes de se explorar o espaço de busca do problema integrado, bem como a utilização de outras meta-heurísticas.
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Dynamische Tourenplanung - Modifikation von klassischen Heuristiken für das Dynamische Rundreiseproblem (DTSP) und das Dynamische Tourenplanungsproblem (DVRP) mit der Möglichkeit der Änderung des aktuellen FahrzeugzugesRichter, Andreas 17 August 2005 (has links)
Unternehmen der Transportbranche müssen gerade im operativen Tagesgeschäft bei der Tourenplanung und Transportdisposition Planungsprobleme lösen, die ein hohes Maß an Dynamik aufweisen. Speziell die Inputfaktoren der Tourenplanung sind größtenteils dynamisch und stochastisch. Aus Sicht des Autors kann die Qualität von Tourplanungsergebnissen durch die zeitnahe Berücksichtigung unvorhergesehener Ereignisse nachhaltig verbessert werden. Jedoch findet diese zunehmend erfolgskritische Funktionalität in der Literatur bisher nur unzureichend Beachtung, obwohl das Tourenplanungsproblem (Vehicle Routing Problem (VRP)) eines der wichtigsten und am meisten erforschten kombinatorischen Optimierungsprobleme ist. Verfahren für kapazitierte dynamische Tourenplanungsproblemstellungen sind in der Literatur kaum zu finden. Speziell im Bereich der Algorithmen, die eine große Lösungsgeschwindigkeit, eine leichte Verständlichkeit, eine aus praktischer Sicht akzeptable Lösungsgüte aufweisen und die Möglichkeit besitzen, die aktuellen Routenpläne der Fahrzeuge ausgehend von der momentanen geographischen Position real-time zu verändern, besteht Forschungsbedarf. Die Arbeit geht daher der Forschungsfrage nach, wie ein Verfahren für die dynamische Tourenplanung zu konstruieren ist, welches das kapazitierte dynamische Tourenplanungsproblem mit der Möglichkeit der Änderung des aktuellen Fahrzeugzuges unter Einhaltung sehr kurzer Rechenzeiten bei größtmöglicher Verständlichkeit löst. Durch die genannten Kriterien wird im Rahmen der Arbeit der Schwerpunkt auf die Modifikation von klassischen heuristischen Verfahren für die Lösung von dynamischen Tourenplanungsproblemen gelegt. Die Arbeit befasst sich sowohl mit dem Gesamtkonzept zur Disposition dynamischer Kunden als auch mit konkreten Modellen und Verfahren zur Lösung von Subproblemen innerhalb des Gesamtkonzeptes. Ferner erfolgt die Präsentation von umfangreichen Simulationsergebnissen, die auf der durchgeführten softwaretechnischen Implementierung der entwickelten Verfahren basieren. Die gute Anwendbarkeit der neuen Verfahren in der Praxis wird gezeigt. Zwecks der möglichst ganzheitlichen Betrachtung des Themengebietes erfolgt in der Arbeit zum einen sowohl die Erörterung von quantitativen als auch von qualitativen Aspekten der dynamischen Tourenplanung und zum anderen die Analyse von Schnittstellen zwischen der dynamischen Tourenplanung und eng damit verbundenen Bereichen wie Flottenmanagement oder Auftragseingang bzw. -disposition. Hierzu werden die Informationsflüsse zwischen den beteiligten Elementen im Rahmen des dynamischen Dispositionsprozesses aufgezeigt, telematische Komponenten zur Unterstützung des Informationsmanagements und der Informationsübertragung vorgestellt sowie die benötigten Inputdaten erläutert. Den Schwerpunkt der Arbeit stellt jedoch die Entwicklung von neuen quantitativen Methoden zur dynamischen Tourenplanung dar.
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Efficient heuristics for large-scale vehicle routing problemsGraf, Benjamin 02 September 2021 (has links)
In this thesis we consider three challenging vehicle routing problems representing specific aspects of complex real-world problems: (i) the vehicle routing problem with unit demands, (ii) the preemptive stacker crane problem and (iii) a multi-period vehicle and technician routing problem. For the vehicle routing problem with units demands we continue research on the exponential multi-insertion neighborhood, investigate its properties and propose heuristic solution methods utilizing the neighborhood. For the preemptive stacker crane problem we study structural properties and provide bounds on the benefits of preemption and the benefits of so-called explicit drop nodes that are used exclusively to facilitate preemption. We propose construction heuristics that improve on the state-of-the-art in computational time and solution quality. The multi-period vehicle and technician routing problem is the subject of the VeRoLog Solver Challenge 2019. We develop a solution method that adapts to the limited computational budget and the given instance parameters. In summary, this thesis contributes to the structural analysis of the considered problems and proposes efficient heuristic solution methods that are effective even on large-scale instances and under tight restrictions of the computational budget. The methods combine global and local search approaches and take the available computational budget into account to realize an adaptive best-effort allocation of the resources.
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Routing for Autonomous Underwater Vehicles : Optimization for subsea operationsJansson, Kasper, Nyberg, Samuel January 2024 (has links)
Background Efficient underwater operations with autonomous underwater vehicles (AUVs) relying on several factors for a mission to be successful, such as operation time, distance covered, and waiting times. Today’s methods and processes for AUVs often struggle with inefficiencies and lack of route optimization. These challenges can result in increased operational costs and suboptimal performance. Minimizing operation time and utilizing route planning algorithms enables adaptation to operational challenges, potentially resulting in cost savings. Objectives This thesis aims to identify an efficient and practical solutions that will improve the operations for AUVs and the objective is to optimize the diving process through suboptimal routing algorithms in a predefined scenario. The study addresses one primary question to achive the aim. The question were: How can routing algorithms be implemented to improve the efficiency and reduce the operation time of Autonomous Underwater Vehicles? Methods The method describes three heuristic algorithms for optimizing the operations of AUVs. The first algorithm, the nearest neighbor heuristic (NNH) aims to minimize the distance an AUV needs to travel to recover and deploy ocean bottom nodes (OBN) within a cluster. The second algorithm, inspired by railway traffic, tries to prevent overlaps and minimizing the waiting times at the depot station. The third algorithm is highlighted as a local optimization algorithm that prioritizes the shortest waiting time over the nearest distance, adapting dynamically to available depot stations. Results The results in this thesis are derived from numerous simulations from different scenarios. The relationship between operations time and waiting time for different scenarios was obtained. The first algorithm proved to work for this type of situation. The second algorithm demonstrated its ability to yield superior solutions, albeit at the cost of being time-consuming due to a high number of iterations. The third algorithm was examined under conditions with and without delays. Even with delays, the algorithm consistently manages disturbances effectively. Conclusions While achieving an exact optimal solution remains challenging due to complexity, the research showed promising improvements in the endurance of the AUVs through the algorithms. The first algorithm was effective in minimizing the distance the AUVs traveled by selecting the most efficient path from numerous potential solutions. The second algorithm was slow due to a large number iterations, but the algorithm was able to find a solution where the operation and waiting time of the AUV could be reduced. The third algorithm was faster, but generally resulted in longer operation times. Also, increasing the number of AUVs resulted in shorter operation times but led to longer waiting times at the depot station, particularly in scenarios that became saturated with too many AUVs. / Bakgrund Undervattensoperationer med autonoma undervattensfarkoster (AUV:er) är beroende av flera faktorer för framgångsrika uppdrag, såsom driftstid, avstånd och väntetider. Dagens metoder och processer för AUV:er har ofta problem med ineffektivitet och bristande optimering av rutter. Dessa utmaningar kan leda till ökade driftkostnader och suboptimal prestanda. Genom att minimera operationstiden och använda ruttplaneringsalgoritmer möjliggörs anpassning till operativa utmaningar, vilket potentiellt kan resultera i kostnadsbesparingar. Syfte Detta examensarbete syftar till att utveckla effektiva och praktiska lösningar för att förbättra systemets prestanda och målet är att optimera rutterna genom suboptimala algoritmer i ett fördefinierat scenario. Arbetet behandlar en primärfråga för att uppnå målet. Frågan var: Hur kan ruttalgoritmer implementeras för att förbättra effektiviteten och minska drifttiden för autonoma undervattensfarkoster? Metod Metoden beskriver tre heuristiska algoritmer för att optimera driften förAUV:er. Den första algoritmen, närmaste granne heuristiken (NNH), syftar till attminimera avståndet en AUV behöver resa för att hämta och placera ut havsbottennoder (OBN) inom en kluster. Den andra algoritmen, inspirerad av tågtrafiken, syftar till att endast en AUV befinner sig vid depåstationen åt gången för att förhindra konflikter och minimera väntetider. Den tredje algoritmen är en lokal optimeringsalgoritm som prioriterar kortaste väntetiden över närmaste avstånd och anpassar sig dynamiskt till tillgängliga depåstationer. Resultat Resultaten i denna uppsats baseras på ett flertal simuleringar med olika scenarier. Förhållandet mellan drifttid och väntetid för olika scenarier erhölls. Den första algoritmen visade sig fungera bra för denna typ av situation. Den andra algoritmen visade sin förmåga att ge bättre lösningar, trots att den var tidskrävande pågrund av ett högt antal iterationer. Den tredje algoritmen undersöktes under förhållanden med och utan förseningar. Trots förseningar lyckades algoritmen konsekvent hantera störningar effektivt. Slutsats Trots komplexiteten med att tillhandahålla en exakt optimal lösning, visade arbetet förbättringar i AUV:ers uthållighet genom olika algoritmer. Den första algoritmen var effektiv för att minimera det avstånd som AUV:er färdades genom att välja en optimal väg bland många potentiella lösningar. Den andra algoritmen var långsam på grund av många iterationer, men algoritmen kunde hitta en lösning där AUV:ens drift- och väntetid kunde minskas. Den tredje algoritmen var snabbare men resulterade i längre drifttider. Vidare resulterade ökningen av antalet AUV:er i en minskning av drifttider men ökade väntetider, särskilt i scenarier som blev mättade med för många AUV:er.
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OPTIMIZATION AND SIMULATION OF JUST-IN-TIME SUPPLY PICKUP AND DELIVERY SYSTEMSChuah, Keng Hoo 01 January 2004 (has links)
A just-in-time supply pickup and delivery system (JSS) manages the logistic operations between a manufacturing plant and its suppliers by controlling the sequence, timing, and frequency of container pickups and parts deliveries, thereby coordinating internal conveyance, external conveyance, and the operation of cross-docking facilities. The system is important to just-in-time production lines that maintain small inventories. This research studies the logistics, supply chain, and production control of JSS. First, a new meta-heuristics approach (taboo search) is developed to solve a general frequency routing (GFR) problem that has been formulated in this dissertation with five types of constraints: flow, space, load, time, and heijunka. Also, a formulation for cross-dock routing (CDR) has been created and solved. Second, seven issues concerning the structure of JSS systems that employ the previously studied common frequency routing (CFR) problem (Chuah and Yingling, in press) are explored to understand their impacts on operational costs of the system. Finally, a discreteevent simulation model is developed to study JSS by looking at different types of variations in demand and studying their impacts on the stability of inventory levels in the system. The results show that GFR routes at high frequencies do not have common frequencies in the solution. There are some common frequencies at medium frequencies and none at low frequency, where effectively the problem is simply a vehicle routing problem (VRP) with time windows. CDR is an extension of VRP-type problems that can be solved quickly with meta-heuristic approaches. GFR, CDR, and CFR are practical routing strategies for JSS with taboo search or other types of meta-heuristics as solvers. By comparing GFR and CFR solutions to the same problems, it is shown that the impacts of CFR restrictions on cost are minimal and in many cases so small as to make simplier CFR routes desirable. The studies of JSS structural features on the operating costs of JSS systems under the assumption of CFR routes yielded interesting results. First, when suppliers are clustered, the routes become more efficient at mid-level, but not high or low, frequencies. Second, the cost increases with the number of suppliers. Third, negotiating broad time windows with suppliers is important for cost control in JSS systems. Fourth, an increase or decrease in production volumes uniformly shifts the solutions cost versus frequency curve. Fifth, increased vehicle capacity is important in reducing costs at low and medium frequencies but far less important at high frequencies. Lastly, load distributions among the suppliers are not important determinants of transportation costs as long as the average loads remain the same. Finally, a one-supplier, one-part-source simulation model shows that the systems inventory level tends to be sticky to the reordering level. JSS is very stable, but it requires reliable transportation to perform well. The impact to changes in kanban levels (e.g., as might occur between route planning intervals when production rates are adjusted) is relatively long term with dynamic after-effects on inventory levels that take a long time to dissapate. A gradual change in kanban levels may be introduced, prior to the changeover, to counter this effect.
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Charging solutions - a route optimization and simulation / Service av laddningscentraler - en ruttoptimering och simuleringSjöholm, Filip, Tivendale, Oliver January 2017 (has links)
Examensarbetet handlar om att minimera en total servicekostnad för företaget Chargestorm då de skall utföra service på sina laddningscentraler för elbilar. En ruttoptimering har gjorts som resulterar i ett antal rutter som är tänka att användas av en servicetekniker när denne åker runt och utför service på laddningscentralerna. En simulering har också gjorts för att påvisa de bästa tidsintervallen då olika typer av service kan ske, med målet att minimera den totala servicekostnaden.
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Aplikace heuristik při řešení rozvozní úlohy / Application of Heuristics on Vehicle Routing ProblemGerlich, Michal January 2011 (has links)
This thesis deals with solving a real case from one specific part of Operations Research -- Discrete Models. The case can be classified as Vehicle Routing Problem (VRP) which is a subset of classical Travelling Salesman Problem (TSP). The VRP is modified TSP when requirements of customers and capacities of trucks play role. The data needed for calculations were taken from the real situation of Pivovar Svijany a.s. The problem can be defined as VRP with cars with different capacities and split delivery. Even though the mathematic model of the problem is known and described in the thesis, the size of the problem is too big to be optimized. Therefore heuristic was used to solve it. Because of the good computational results in the past the savings algorithm was chosen. Its model was set using Visual Basic for Applications (VBA). The thesis (among others) analyses the sensitivity of the output on the values of the factors that can be chosen by the analyst. At the end of the thesis the best found solution is presented and the initial and the new scheme of the circles are compared.
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A meta-heurística busca dispersa em problemas de roteirização com coleta e entrega simultâneas: aplicação na Força Aérea Brasileira. / The scatter search metaheuristic in vehicle routing problems with simultaneous delivery and pickup: application in the brazilian air force.Mesquita, Antônio Célio Pereira de 08 April 2010 (has links)
O presente trabalho trata da solução para o problema da elaboração de programações de transporte do sistema de distribuição de materiais da Força Aérea Brasileira (FAB). Essas programações de transporte consistem em definir os roteiros de entrega e coleta de materiais a serem realizadas simultaneamente em cada local de entrega/coleta a partir de um centro de distribuição, considerando-se a frota de veículos homogênea. Isto é característico de um Problema de Roteirização de Veículos com Coletas e Entregas Simultâneas (PRVCES). A gestão do sistema de distribuição física da FAB considera a complexidade desse sistema e os dados relativos às demandas de transporte de carga em cada um desses locais para elaborar as programações de transporte. Essas programações são elaboradas tendo em vista os limites de capacidade dos veículos, as características físicas das cargas e as prioridades de embarque. O gestor desse sistema possui boa visibilidade das demandas de transporte, porém, devido à grande quantidade de informações disponíveis e à elevada complexidade desse sistema, é impossível elaborarem-se manualmente programações de transporte que resultem em viagens de distribuição eficientes. O PRVCES foi resolvido por meio da meta-heurística Busca Dispersa (do inglês Scatter Search) integrada com a meta-heurística Descida em Vizinhança Variável (do inglês Variable Neighborhood Descent) utilizada como método de melhoria das soluções. Os resultados superaram ou se igualaram a alguns dos obtidos por outros autores para os mesmos problemas de teste com as mesmas restrições, o que demonstra que a Busca Dispersa implementada é competitiva para solucionar o PRVCES. Quanto à aplicação na FAB, os resultados mostraram que a utilização do método de solução desenvolvido resultará em programações de transporte elaboradas em curto tempo de processamento e que estas incidirão positivamente sobre a eficiência do sistema de distribuição de materiais da FAB. / This work deals with the solution to the problem of drawing up transport schedules in the material distribution system of the Brazilian Air Force (BAF). These transport schedules consist in defining the routes for material pickup and delivery to be accomplished simultaneously in each delivery/pickup location from a distribution center, considering a homogeneous fleet of vehicles. This is characteristic of a Vehicle Routing Problem with Simultaneous Delivery and Pick-up (VRPSDP). The management of the physical distribution of BAF considers the complexity of this system and the data regarding the cargo transport demands in each one of those locations to draw up transport schedules. These schedules are drawn up regarding the capacity limits of the vehicles, the physical characteristics of the cargoes and the shipping priorities. A good visibility of transport demands in each location is available to the manager of this system, but due to the great quantity of data to deal with and the high complexity of the physical distribution system of BAF, it is impossible to draw up transport schedules that result in efficient distribution trips. The VRPSDP was solved by means of the Scatter Search meta-heuristic integrated with the Variable Neighborhood Descent meta-heuristic as the solution improvement method. The results exceeded or equaled some of those obtained by other authors using the same test problems with the same restrictions, what indicates that the implemented Scatter Search is competitive to solve the VRPSDP. As for the application in the BAF, the results showed that using the solution method developed will result in schedules drawn up in short processing time and focused on the efficiency of the material distribution system of the BAF.
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Modelagem heurística no problema de distribuição de cargas fracionadas de cimento. / Heuristic modeling in the less-than-truckload cement distribution problem.Miura, Marcos 11 September 2008 (has links)
Esta dissertação trata do problema do agrupamento de cargas fracionadas na distribuição de cimento ensacado partindo de um depósito central. O problema consiste em definir quais entregas de cimento serão carregadas juntas em um determinado veículo, de modo a aproveitar ao máximo sua capacidade e ao mesmo tempo reduzir o custo com o frete pago aos transportadores que farão sua distribuição. Em especial, o método de resolução proposto pode ser dividido em três fases. Na primeira fase, as entregas pertencentes a um mesmo cliente são agrupadas prioritariamente. Na segunda fase, são agrupadas as entregas de clientes dentro de uma mesma cidade. Neste caso, uma simplificação necessária é considerar que todas as entregas de uma mesma cidade estão localizadas em um único ponto. Com isso, a distância entre os clientes se torna irrelevante e é proposto um método baseado em um algoritmo genético para resolução de problemas de bin-packing (BPP). Para a terceira fase, é considerado o agrupamento para pontos de entrega pertencentes a cidades diferentes, onde as distâncias rodoviárias são consideradas. Nesta etapa, é proposta uma variação do método anterior, incorporando ao modelo algumas heurísticas para resolução de problemas de roteirização de veículos, como o algoritmo de Clarke & Wright e o algoritmo do Vizinho Mais Próximo. / This thesis deals with the problem of merging less-than-truckload deliveries in bagged cement distribution from a central depot. The problem consists in defining which cement deliveries shall be loaded in each given vehicle, in order to maximize the vehicle full capacity as well as reduce carriers freights. Particularly, the solution method can be divided hierarchically in three stages. In the first stage, the deliveries from the same client are merged with priority. In the second stage, the deliveries from the same city are merged. In this case, a necessary assumption is to consider the deliveries from the same city as located in a single destination point. Consequently, the distances among deliveries can be assumed as irrelevant and a heuristic method is proposed, which relies on a genetic algorithm for the bin-packing problem (BPP). In the third stage, merging of different delivery points that are apart from each other is considered. For this step, a variation of the previous method is proposed, incorporating some heuristics to solve the vehicle routing problem, like the Clarke & Wrights savings algorithm and the Nearest Neighbor algorithm.
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Heurísticas para o problema de distribuição com estoques geridos pelo fornecedor. / Heuristics for the vendor managed inventory problem.Znamensky, Andrei 20 October 2006 (has links)
O presente trabalho aborda o sistema logístico usualmente denominado Vendor Managed Inventory (VMI), no qual o fornecedor controla e coordena as decisões de reabastecimento, sendo responsável por manter os estoques de seus clientes dentro de limites fixados de antemão. O modelo proposto incorpora ainda as decisões relativas à produção e manutenção de estoque por parte do fornecedor, além da utilização de frota heterogênea na distribuição, e busca a minimização dos custos totais do sistema. Quatro heurísticas de duas etapas são propostas para a resolução do problema abordado. A primeira etapa, comum a todas as heurísticas, baseia-se em uma heurística recentemente publicada na literatura e fornece uma solução inicial viável, utilizada como ponto de partida para a etapa de melhoria subsequente, na qual é utilizada a metaheurística busca tabu ou busca em vizinhança variável. As heurísticas propostas foram avaliadas em um conjunto de teste, sendo obtidos resultados melhores que os reportados na literatura em todas as instâncias testadas. Dentre as estratégias de solução avaliadas, destaca-se a heurística baseada em busca tabu com diversificação, que demonstrou ser superior às demais heurísticas propostas. Os resultados obtidos indicam ainda que, no caso da frota disponível ser heterogênea, é vantajosa a utilização de uma adaptação do procedimento de obtenção da solução inicial, como forma de privilegiar a utilização de veículos de maior eficiência. / This thesis deals with the logistic system usually called Vendor Managed Inventory (VMI). In this system the supplier controls and coordinates the supply decisions and is responsible for keeping the inventory of each of his clients within predetermined minimum and maximum levels. Heterogeneous fleet and production/stocking decisions at the supplier are considered as well, and the proposed model seeks to minimize the total system cost. Four two-stage heuristics are proposed for this problem. The first stage consists in an adaptation of a heuristic found in the bibliography, which provides an initial viable solution that will be improved in the second stage by means of the metaheuristics tabu search or variable neighborhood search. The proposed heuristics were tested on a set of benchmark instances with improvements found on the best known results in all of the tested instances. The obtained results indicate that the tabu search based heuristic with diversification strategy is clearly superior to the other proposed heuristics and that a better fleet utilization can be obtained in the case of heterogeneous fleet by a simple improvement in the first stage, that favors the selection of more efficient vehicles.
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