In this thesis, the seat inventory control problem is studied for airlines from the perspective of a risk-averse decision maker. There are only a few studies in the revenue management literature that consider the risk factor. Most of the studies aim at finding the optimal seat allocations while maximizing the expected revenue and do not take the variability of the revenue and hence a risk measure into account. This study aims to decrease the variance of the revenue by increasing the capacity utilization called load factor in the revenue management literature. In addition to expected revenue, load factor is an important performance measure the state companies work with. For this purpose, two types of models with load factor formulations are proposed. This thesis is the first study in the revenue management literature for the airline industry that uses the load factor formulations in the mathematical models. It is an advantage to work with load factor formulations since the models with load factor formulations are much easier to formulate and solve as compared to other risk sensitive models in the literature. The results of the proposed models are evaluated by using simulation for a sample network under different scenarios. The models we propose allow us to control the variability of revenue by changing the used capacity of the aircraft. This is at the expense of a decrease in the revenue under some scenarios. The models we propose perform satisfactorily under all scenarios and they are strongly recommended to be used especially for the small-scale airline companies and state companies and for scheduling new flights even in large scale, well established airline companies.

In this study, we focus on a real life problem that involves a single item which is used in military operations. The items in use fail according to a Poisson process and lead times are deterministic. Four alternative inventory control models are developed. Among these models, a two-echelon system consisting of a depot in the upper and several bases in the lower echelon is operated currently. This system is compared to a single-echelon system that consists of several bases. The comparison reveals the importance of the holding cost incurred for the items intransit between the depot and the base which is ignored in most of the studies in literature. Both the two and single-echelon models are also extended to have repair ability. A continuous-review base-stock policy is used for all models. Exact models are formulated. The results are obtained under various lead time, unit costs and demand parameters. Results of four different settings are compared and the findings are reported.

Thesis (M.S.)--Mississippi State University. Department of Industrial and Systems Engineering. / Title from title screen. Includes bibliographical references.

Face à une concurrence féroce par suite de la modélisation économique, les entreprises doivent bien gérer leurs chaînes logistiques afin de réduire leurs coûts d’exploitation tout en améliorant leurs services au client. Un enjeu majeur de cette gestion et la gestion efficace des stocks multi-échelons. Dans cette thèse, nous étudions des systèmes de stocks multi-échelons avec des coûts de passation de commande à chaque stock. En raison de l’existence des coûts de passation de commande, l’optimisation d’un tel système devient très compliquée. Récemment, l’approche de service garanti (GSA) a été utilisée pour déterminer les stocks de sécurité pour les systèmes de stocks multi-échelons, mais sans coûts fixes de passation de commande. Nous généralisons la GSA pour optimiser la politique de stockage (R, Q) d’un système de stocks multi-échelons avec la demande suivant un processus de Poisson et coûts fixes de passation de commande à chaque stock. Nous considérons trois types de systèmes de stocks multi-échelons, et pour chaque type, nous d'abord établissons un modèle mathématique pour le problème d’optimisation. Ensuite, le modèle est résolu par une procédure itérative fondée sur deux algorithmes de programmation dynamique (DP). Un algorithme DP est utilisé pour résoudre le sous-problème de détermination de quantités de commande et l'autre est utilisé pour résoudre le sous-problème de détermination de points de recommande du modèle. Les résultats numériques démontrent l'efficacité des algorithmes et de la procédure / With the increasing complexity of supply chains led by economic globalization, integrated supply chain management has become an important strategy utilized by the firms to reduce the overall cost while meeting the customer service. This change has made academic researchers and industrial practitioners pay more and more attention to multi-echelon inventory management over the last two decades. In this thesis, we study multi-echelon inventory systems with fixed order costs at each stock. Because of the existence of fixed order costs, the optimization of such system becomes very complicated. Recently, Guaranteed Service Approach (GSA) was used to set safety stock for multi-echelon inventory systems, but without fixed order costs. We extend the GSA to optimize (R, Q) inventory policies for multi-echelon inventory systems with Poisson demand and fixed order costs. Our objective is to find optimal (R, Q) policy for such a system so that its total cost is minimized while achieving a service level to customer. Three types of multi-echelon inventory systems, serial systems, assembly systems and two-level distribution systems are considered. For each type, we first establish a mathematical model for the optimization problem. Then, the model is solved by an iterative procedure based on two dynamic programming (DP) algorithms. One DP algorithm is used to solve the order size decision subproblem and the other is used to solve the reorder point decision subproblem of the model. Numerical experiments demonstrate the efficiency of the algorithms and the procedure

Cette thèse considère le problème consistant à intégrer les décisions de routage et stockage lors de la conception de la chaîne logistique. Le but est de sélectionner des dépôts parmi un ensemble de candidats pour desservir un ensemble de détaillants à l’aide d’une flotte de véhicules de capacité permettant visiter plus d’un détaillant par route. On cherche à déterminer la localisation de ces dépôts et les tournées des véhicules afin de maintenir leurs niveaux optimaux de stocks. La demande chez les détaillants est connue à l’avance. Des applications dans les domaines de la logistique humanitaire et militaire sont envisageables. Pour résoudre le problème, deux matheuristiques sont proposées. Dans la première partie, une méthode coopérative qui combine des méthodes exactes pour le problème de conception de la chaîne logistique et des méthodes heuristiques de routage est présentée. Dans la deuxième partie, une méthode de décomposition utilisant une réformulation de Dantzig-Wolf sur les variables de routage est proposée. L’algorithme intègre les concepts de génération de colonnes, relaxation lagrangienne et recherche locale. Les résultats montrent la capacité des algorithmes à trouver des solutions de bonne qualité et nous estimons de façon empirique l’impact de considérer un modèle intégré au lieu d’utiliser une méthode d’optimisation séquentielle. De plus, les résultats des méthodes présentées sur des sous-problèmes sont aussi étudiés. Ces sont: le problème de localisation-routage, le problème de tournées avec gestion de stocks, et le problème de plus court chemin généralisé / The problem of designing a supply chain including simultaneously routing and inventory management decisions is studied in this thesis. The objective is to select a subset of depots to open, the inventory policies for a 2-echelon system, and the set of routes to perform distribution from the upper echelon to the next using a homogeneous fleet of vehicles over a finite planning horizon. Demand is considered to be known. Applications are found in humanitarian logistics and military logistics. To solve the problem, two matheuristic procedures are developed. On the first part a cooperative algorithm combining exact methods for the supply chain design problem and routing heuristics is presented. On the second part, a partition is proposed using a Dantzig-Wolf reformulation on the routing variables. An hybridization between column generation, Lagrangian relaxation and local search is proposed in this part, put together as a heuristic method. Furthermore, results demonstrate the capability of the algorithms to compute high quality solutions and empirically estimate the improvement in the cost function of the proposed model when compared to a sequential optimization approach. Furthermore, results of the proposed methodologies on benchmark instances for subproblems are studied as well. Those are the capacitated location-routing problem, the inventory-routing problem, and the generalized elementary shortest path problem

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2016-09-28T13:16:37Z No. of bitstreams: 1 ORTIZ_Erica_2015.pdf: 2217131 bytes, checksum: 5db14ac14252df90c693639ce9b84e6b (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2016-09-28T13:17:26Z (GMT) No. of bitstreams: 1 ORTIZ_Erica_2015.pdf: 2217131 bytes, checksum: 5db14ac14252df90c693639ce9b84e6b (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2016-09-28T13:17:52Z (GMT) No. of bitstreams: 1 ORTIZ_Erica_2015.pdf: 2217131 bytes, checksum: 5db14ac14252df90c693639ce9b84e6b (MD5) / Made available in DSpace on 2016-09-28T13:24:04Z (GMT). No. of bitstreams: 1 ORTIZ_Erica_2015.pdf: 2217131 bytes, checksum: 5db14ac14252df90c693639ce9b84e6b (MD5) Previous issue date: 2015-12-09 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Remanufacture can be defined as the industrial process where products worn, broken or used are restored getting a new life. Currently, many companies remanufactured products, driven by economic or environmental benefits, or by the force of law. Performing materials management and inventory in this environment with peculiar characteristics efficiently, it is necessary to contain waste with excess inventory or lack of material for production. In addition, the purchasing department holds an important position in most organizations, as parts, components and supplies can represent 40-60% of the final value of sales of any product. Thus, the objective of this work is the proposition and implementation of inventory management models in a remanufacturing company of fire extinguishers and analyze the efficiency of these through the expenses accumulated during one quarter. Based on preliminary analysis of the historical consumption series of selected materials, three propositions were suggested. The results show that when we analyzed the implementation of the proposals in material individually, there were cost reductions and better regularity in buying some, and in others, the proposals have not brought benefits. With the results, it is suggested that the application of the propositions, even partially for some materials, can help to increase the company's competitiveness with the availability of capital that was previously allocated to the purchase of these. / A remanufatura pode ser definida como o processo industrial onde produtos desgastados, quebrados ou usados, são restaurados obtendo uma nova vida útil. Na atualidade, muitas empresas remanufaturam produtos, impulsionadas pelas vantagens econômicas ou ambientais, ou por força da legislação. Realizar a gestão de materiais e estoque neste ambiente com características peculiares, de forma eficiente, é necessário para se conter desperdícios com excesso de estoque ou falta de materiais para a produção. Além disso, o setor de compras ocupa uma posição importante na maioria das organizações, pois peças, componentes e suprimentos comprados podem representar de 40 a 60% do valor final das vendas de qualquer produto. Com isso, o objetivo desse trabalho é a proposição e a aplicação de modelos de gestão de estoque e materiais em uma empresa de remanufatura de extintores de incêndio e analisar a eficiência destes através dos gastos acumulados durante um trimestre. Com base nas análises preliminares das séries históricas do consumo dos materiais selecionados, foram sugeridas três proposições. Os resultados encontrados apontam que quando analisamos a implementação das proposições nos materiais de forma individual, houve reduções nos custos e melhor regularidade na compra de alguns, e em outros, as proposições não trouxeram benefícios. Com os resultados, sugere-se que a aplicação das proposições, mesmo que parcialmente para alguns materiais, pode contribuir para aumentar a competitividade da empresa com a disponibilidade de capital que antes estava alocado com a compra desses.

Orientador: Fernando José Von Zuben / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-17T20:59:25Z (GMT). No. of bitstreams: 1 Azuma_ReginaMitsue_M.pdf: 2321816 bytes, checksum: 44c4417bf2a4fad2a8241c7189e4d04a (MD5) Previous issue date: 2011 / Resumo: A classe de problemas de estoque e roteamento está presente em várias áreas, incluindo indústria automobilística e gerência de numerário no reabastecimento de caixas eletrônicos. Supondo que o fornecedor é responsável pela estocagem e distribuição dos produtos, sujeito a um conjunto de restrições, o desafio que se apresenta é a determinação de uma política ótima, mais especificamente quais clientes atender, qual quantidade a ser fornecida a cada cliente e qual rota empregar visando a minimização dos custos. Este trabalho apresenta uma proposta de solução para uma das mais comuns formulações do problema: um produto é distribuído a partir de um fornecedor para vários clientes em um horizonte de tempo definido. O transporte é realizado por um veículo de capacidade limitada. Para produzir a otimização simultânea de ambos os objetivos, minimização dos custos de transporte e estoque, a proposta segue uma abordagem multiobjetivo e se baseia no uso do algoritmo SPEA2 (do inglês, Strength Pareto Evolutionary Algorithm 2), incluindo inovações na representação de soluções-candidatas, nos operadores genéticos e de busca local. A fronteira de Pareto estimada é então composta de múltiplas soluções não-dominadas, representando compromissos distintos entre custos de transporte e estoque. Como casos de estudo, são tomadas instâncias de médio porte extraídas da literatura e são geradas instâncias de grande porte. Para as instâncias de médio porte, as fronteiras de Pareto estimadas em cada caso são comparadas com as respectivas soluções ótimas da versão mono-objetivo de cada problema, pois já existe um algoritmo exato de solução para a formulação mono-objetivo de instâncias de médio porte / Abstract: The class of inventory routing problems (IRP) is present in several areas, including automotive industry and cash management for ATM networks. Given that the supplier is responsible for managing the product inventory and replenishment, subject to a set of restrictions, the challenge here is to determine an optimal policy, more specifically which retailers to serve, the quantity to deliver to each retailer and which routes to employ in order to minimize the cost. This work presents a proposal to solve one version of the IRP usually found in the scientific literature: a product is distributed from a supplier to several retailers in a defined time horizon. Shipment is performed by a vehicle with limited capacity. To perform the simultaneous optimization of both objectives, minimization of transportation and inventory costs, the proposal follows a multi-objective approach based on SPEA2 (Strength Pareto Evolutionary Algorithm 2), including innovative aspects mainly associated with the representation of candidate solutions, genetic operators and local search. The Pareto front is then composed of multiple non-dominated solutions with distinct trade-offs between transportation and inventory costs. As case studies, medium size instances extracted from the literature are considered and large size instances are generated. For the medium size instances, the estimated Pareto fronts are compared, in each case, with the corresponding optimal solutions associated with the single-objective version of each problem, given that there is already an exact algorithm to solve such medium size single-objective instances / Mestrado / Engenharia de Computação / Mestre em Engenharia Elétrica

Orientador: Antonio Batocchio / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-08T14:39:58Z (GMT). No. of bitstreams: 1 Dagnone_CarlosAugustoFernandes_D.pdf: 4873205 bytes, checksum: b23d781adbe55441373668533ae3cc87 (MD5) Previous issue date: 2006 / Resumo: No presente trabalho é apresentada uma proposta de ambiente computacional cuja finalidade é auxiliar na coordenação de processos de aquisição de bens do setor metal-mecânico entre empresas integradas por redes de fornecedores. Para atingir este objetivo, foi executada uma pesquisa bibliográfica sobre os conceitos envolvendo o gerenciamento da cadeia de suprimentos, controle de estoques intermediários e de segurança e tecnologias associadas à comunicação em redes de computadores e simulação de sistemas. Como resultado, foi desenvolvido o SIPES (Sistema de Informação para o Planejamento de Estoques baseado em Simulação), uma plataforma que implanta os resultados teóricos discutidos e é responsável por gerar estimativas de níveis de estoques a partir de demandas conhecidas e de informações fornecidas por modelos de simulação da produção das empresas envolvidas. Pretende-se, deste modo, aproximar os elos da cadeia de suprimentos em termos de seus requerimentos de compras em lugar de priorizar estratégias individuais para esta função, além de tornar disponível um ambiente passível de incrementos futuros / Abstract: This work is intended to presents a proposal of a computer environment framework whose objective is to help in coordinating the acquisition process of goods of the metal-mechanic sector among organizations integrated by supplier chains. To achieve this, a bibliographic research was made about concepts involving supply chain management, cycle and safety inventory control and technologies linked to computer networks communications and systems simulation. As an outcome, SIPES (Computer Simulation-based Information System for Inventory Planning) was developed, a platform that implements the theoretical aspects discussed and whose aim is to generate inventory level estimates under known demands and results from production simulation of the related enterprises. The idea is to group them around common buying requirements instead of prioritize a single enterprise's individual strategies for this function, as well as to provide an environment that can receive further improvements / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Orientador: Fernando José Von Zuben / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-25T22:55:48Z (GMT). No. of bitstreams: 1 Raimundo_MarcosMedeiros_M.pdf: 764820 bytes, checksum: 80ad4c20c482ad09b06c3e07d1b2c240 (MD5) Previous issue date: 2014 / Resumo: O gerenciamento de cadeias de suprimento no mundo corporativo é de grande relevância prática e uma de suas versões é conhecida como problema de roteamento e estoque. Este trabalho propõe uma formulação linear-inteira genérica e flexível para este problema de otimização, assim como uma metodologia de solução. Nesta nova formulação proposta, algumas peculiaridades da rede de suprimentos podem ser especificadas como parâmetros de entrada, permitindo assim que o usuário seja capaz de realizar modificações na estrutura, na hierarquia e no elenco de restrições da cadeia de suprimentos, sem precisar refazer a formulação matemática associada. Com isso, é possível resolver uma grande diversidade de configurações do problema, sem a necessidade de adaptações junto à metodologia de solução. A natureza genérica e flexível da formulação linear-inteira se deve às seguintes propriedades, todas elas passíveis de serem definidas como parâmetros de entrada: (1) Todo nó da rede pode produzir ou consumir produtos; (2) Todo nó da rede pode enviar e receber produtos; (3) Decorrente das propriedades (1) e (2), a hierarquia de entrega fica generalizada, com o produto podendo passar por vários nós antes de ser consumido; (4) Restrições presentes na formulação garantem consistência, por exemplo, entre quantidade de produto entregue pelos fornecedores e recebida pelos consumidores; (5) Restrições presentes na formulação estão associadas a especificações que podem ser ativadas, como intervalo de tempo entre entregas. Os resultados experimentais contemplam soluções para múltiplas configurações do problema, todas representáveis pela formulação proposta e, portanto, todas resolvidas pela mesma metodologia de solução. Essas múltiplas configurações trabalhadas nos experimentos evidenciam os benefícios do emprego de uma formulação estendida para o problema de roteamento e estoque. Além disso, visando comparação com propostas alternativas disponíveis na literatura, tomou-se uma configuração específica e bem-estabelecida do problema, para a qual existe uma formulação própria e uma metodologia de solução dedicada. Neste experimento comparativo, chegou-se às mesmas soluções e, em algumas parametrizações, até a soluções de melhor qualidade / Abstract: Managing supply chains in the corporate world is of great practical relevance and one of its versions is named inventory routing problem. This work proposes a more generic and flexible linear-integer formulation for this optimization problem, together with a solution methodology. In the novel formulation proposed here, some peculiarities of the supply network can be specified as input parameters, thus allowing the user to make modifications to the structure, the hierarchy and the set of constraints in the supply chain, without having to rebuild the associated mathematical formulation. Therefore, it is possible to solve a wide variety of configurations of the problem without the need for adjustments in the solution methodology. The generic and flexible nature of the linear-integer formulation is due to the following properties, all of them being definable as input parameters: (1) Every node of the network can produce or consume products; (2) Every node of the network can send and receive products; (3) Due to properties (1) and (2), the hierarchy of delivery is generalized, with the product being able to pass through several nodes before being consumed; (4) Some restrictions of the formulation ensure consistency, for example, between the amount of product delivered by the suppliers and received by the consumers; (5) Some restrictions of the formulation are associated with specifications that can be activated, as the time interval between deliveries. The experimental results include solutions for multiple configurations of the problem, all representable by the proposed formulation and, as a consequence, all able to be solved by the same solution methodology. Those multiple configurations considered in the experiments highlight the benefits of employing an extended formulation for the inventory routing problem. Aiming at comparing to alternative proposals available in the literature, it was considered a specific and well-established configuration of the problem, for which there are a proper formulation and a dedicated solution methodology. In this comparative experiment, we came to the same solutions and, in some parameterizations, even better solutions / Mestrado / Engenharia de Computação / Mestre em Engenharia Elétrica

Magister Pharmaceuticae - MPharm / South Africa is faced with a high number of people living with HIV/AIDS, and subsequently a great need to access quality medicines for improving patient therapeutic outcomes. Antiretroviral drugs (ARVs) require rigid, efficient and effective management, due to their valuable efficacy in prolonging the survival of HIV/AIDS patients, and the limited possibility of substitution. Managing their flow is vital to ensure an uninterrupted supply. Problematic inventory management was experienced by some healthcare facilities in South Africa where in recent years it resulted in stock outs and stock losses through thefts. These factors present obstacles to the availability of quality medicines, which ultimately leads to treatment failure and deterioration of the health status of patients. The aim of this study was to characterise the inventory management practices and medicine store maintenance of ARVs in community health centres (CHCs) in the Cape Metropole, Western Cape, in order to identify specific problems associated with ARV stock management. The study used a descriptive, cross-sectional study design to examine ARV records and to highlight associated discrepancies between recorded iii quantities on logistics tools used and physical counts, to assess the store maintenance, to measure the supply rate and identify factors contributing to poor stock management. The sample comprised 15 CHCs under the Western Cape Provincial Government (WCPG) accredited to provide ARV treatment. A checklist developed by Management Sciences for Health was adapted and was used to gather quantitative information (e.g. physical stock count). Some qualitative data was collected from responsible personnel for ARV drug management at each site. 86.7% of CHCs utilised a logistics tool (either manual or electronic) to manage ARVs. The average number of adult ARV drugs with a logistics tool available in all CHCs was 82.7% of which 21.9% met the criteria for accuracy. Only 32.9% of all logistics tools had records that were up to date. The average percentage of total variation between stock records and physical counts for the ARV drugs assessed was 51.6%. No historical data on stock outs and monthly usage (monthly consumption) could be retrieved in any of the CHCs, although there were no actual stock outs on the day of the fieldwork. The order fill rate was 91.9%. Since ordering is done more often that it should, stock availability did not appear to be problematic. Standard appropriate physical dimensions were not met by 20% of the CHCs and only 66.7% of the CHCs had appropriate labeling of the shelves in the dispensary and in the storeroom. This study demonstrated poor inventory management with respect to the general quality of record keeping, space allocation and general organisation of the medicine storeroom. Making timely entries and recording issues on logistics tools are recommended to keep up to date inventory records and management information system. Frequent monitoring of stock status is suggested, to avoid discrepancies and to keep it to adequate levels iv which will minimise multiple ordering. Regular supervision by the district pharmacist is needed to identify training and other needs. A study on general cost and delivery costs associated with poor record keeping should be carried out.