Dissertations / Theses on the topic 'Inventory and distribution logistics'

The industrial gas industry represents a multi-billion dollar global market and provides essential product to manufacturing and service organizations that drive the global economy. In this dissertation, we focus on improving distribution efficiency in the industrial gas industry by addressing the strategic level problem of bulk tank allocation (BTA) while considering the effects of important operational issues. The BTA problem determines the preferred size of bulk tanks to assign to customer sites to minimize recurring gas distribution costs and initial tank installation costs. The BTA problem has a unique structure which includes a resource allocation problem and an underlying vehicle routing problem with split deliveries. In this dissertation, we provide an exact solution approach that solves the BTA problem to optimality and recommends tank allocations, provides a set of delivery routes, and determines delivery amounts to customers on each delivery route within reasonable computational time. The exact solution approach is based on a branch-and-price algorithm that solves problem instances with up to 40 customers in reasonable computational time. Due to the complexity of the problem and the size of industry representative problems, the solution approaches published in the literature rely on heuristics that require a set of potential routes as input. In this research, we investigate and compare three alternative route generation algorithms using data sets from an industry partner. When comparing the routes generation algorithms, a sweep-based heuristic was the preferred heuristic for the data sets evaluated. The existing BTA solution approaches in the literature also assume a single bulk tank can be allocated at each customer site. While this assumption is valid for some customers due to space limitations, other customer sites may have the capability to accommodate multiple tanks. We propose two alternative mathematical models to explore the possibility and potential benefits of allocating multiple tanks at designated customer site that have the capacity to accommodate more than one tank. In a case study with 20 customers, allowing multiple tank allocation yield 13% reduction in total costs. In practice, industrial gas customer demands frequently vary by time period. Thus, it is important to allocate tanks to effectively accommodate time varying demand. Therefore, we develop a bulk tank allocation model for time varying demand (BTATVD) which captures changing demands by period for each customer. Adding this time dimension increases complexity. Therefore, we present three decomposition-based solution approaches. In the first two approaches, the problem is decomposed and a restricted master problem is solved. For the third approach, a two phase periodically restricting heuristic approach is developed. We evaluate the solution approaches using data sets provided by an industrial partner and solve the problem instances with up to 200 customers. The results yield approximately 10% in total savings and 20% in distribution cost savings over a 7 year time horizon. The results of this research provide effective approaches to address a variety of distribution issues faced by the industrial gas industry. The case study results demonstrate the potential improvements for distribution efficiency.
Ph. D.

Master´s thesis is solved in business enterprise focused on end user, proceeding demand prognosis. With concentration on solution and optimizing transport costs in options (production enterprise inventory, cross-docking), inventory management and logistic network in enterprise.

In the Master’s Thesis, the management of processing of an order in the company Pekárny Blansko, a.s., is analyzed. The description of the present way of dealing with the orders is included in the Thesis as well. Subsequently, the Thesis contains a proposal that facilitates meeting the customers’ demands for quantity and time. This solution will contribute to the competitive advantage of the company in the market.

The elimination of distribution inefficiencies, occurring due to the timing of customers' orders is an important reason for companies to introduce vendor managed inventory programs. By managing their customers' inventories, suppliers may be able to reduce demand variability and therefore distribution costs. We develop technology to measure the effectiveness of distribution strategies. We develop a methodology that allows the computation of tight lower bounds on the total mileage required to satisfy customer demand over a period of time. As a result, companies will be able to gain insight into the effectiveness of their distribution strategy. This technology can also be used to suggest desirable delivery patterns and to analyze tactical and strategic decisions. Secondly, we study the inventory routing problem with continuous moves (IRP-CM). The typical inventory routing problem deals with the repeated distribution of a single product, from a single facility, with an unlimited supply, to a set of customers that can all be reached with out-and-back trips. Unfortunately, this is not always the reality. We introduce the IRP-CM to study two important real-life complexities: limited product availabilities at facilities and customers that cannot be served using out-and-back tours. We need to design delivery tours spanning several days, covering huge geographic areas, and involving product pickups at different facilities. We develop a heuristic and an optimization algorithm to construct distribution plans. The heuristic is an innovative randomized greedy algorithm, which includes linear programming based postprocessing technology. To solve the IRP-CM to optimality, we give a time-discretized integer programming model and develop a branch-and-cut algorithm. As instances of time-discretized models tend to be large we discuss several possibilities for reducing the problem size. We introduce a set of valid inequalities, called delivery cover inequalities, in order to tighten the bounds given by the LP relaxation of the time-discretized model. We also introduce branching schemes exploiting the underlying structure of the IRP-CM. An extensive computational study demonstrates the effectiveness of the optimization algorithm. Finally, we present an integrated approach using heuristics and optimization algorithms providing effective and efficient technology for solving inventory problems with continuous moves.

Aim: More and more organizations worldwide want to develop products for global markets. At the same time, they need to make their products available in the global market to be competitive. One of today's trends to solve this problem of making products in the global market is by involving logistics to manage complex distribution requirements. Organizations have developed strategic alliances with companies all over the world to manage their logistics operations network. (www.chrobinson.com).

My research was aimed at understanding the coordination of logistics activities at the terminal.

 

Method: I based my study on a combination of descriptive and exploratory type. As regards descriptive I presented my data collected in a descriptive analysis. Also I used the exploratory research to know exactly the implementation of logistics activities at Schenker's terminal and also to observe the activities, conduct interviews and administer questionnaires.

 

Result & Conclusions: The major results of my findings revealed that the existing management procedure of the outbound logistics system at Schenker terminal which involves material handling, transportation, distribution, cross-docking, customer service and information systems could not be seen as lean and agile. This is because of the existence of many problems faced by the terminal such as congestion, flows inefficiencies, excess scrap, too much manual documentation,  delays in deliveries, damages, poor customer service, return goods, idle equipment (forklift and trucks) and personal and high cost of operations.

 

Suggestions for future research: The study is limited in the sense that it does not include the whole supply chain; the terminal is just a part in the supply chain and whatever problems that are encountered are not experienced in the whole supply chain. This could lead to a broader basis of a future research project.

Natural and man-made disasters are becoming more frequent in many countries throughout the world. Countries with inadequate infrastructure and poorly planned emergency logistics are subject to such events which may lead to the destruction of a community and/or may prevent e cient and successful recovery. Despite the progress that disaster planning, mitigation and new management systems have made, the need for disaster relief continues everlasting. Extensive research is on-going to improve the various phases in the disaster operations life cycle. However, the impact of disaster will not diminish and improved disaster relief planning and management should be addressed intensely. This dissertation addresses various possible mathematical models comprising stochastic and deterministic models, to provide generic means to address the damage and consequences associated with disaster events. The models are applied to countries such as Somalia and the Southern African Development Community (SADC), which have been prone to catastrophic events and poverty consequences.
Dissertation (MEng)--University of Pretoria, 2012.
Industrial and Systems Engineering
unrestricted

"Submitted in partial fulfillment of the requirements for the degree of Master of Business Administration from the Naval Postgraduate School, June 2010."
Advisor(s): Yoho, Keenan D. ; Brinkley, Douglas E. "June 2010." "MBA Professional report"--Cover. Description based on title screen as viewed on July 14, 2010. Author(s) subject terms: Inventory management, records keeper, stores onload process. Includes bibliographical references (p. 59). Also available in print.

Recycling and remanufacturing returned goods are economically beneficial for companies since the cost of obtaining used parts is lower in many cases and selling price is close to that of a new product. This leads to decreased costs and thereby increased profits for the company. In addition, there are also great environmental benefits by keeping the structural integrity of a part; the energy used for disassembly and refurbishing is much lower than the energy required for raw material extraction and machining. Encompassing the returned goods makes the supply chain to closed loop supply chain, which is different from the traditional supply chain due to reverse logistics. A reverse flow of material is however usually more complex than a forward flow of parts and components from suppliers. This means that inventory management becomes critical and needs to be viewed from a new perspective. The purpose of the report is to study FAW Co., Ltd’s inventory situation in reverse logistics. The report analysed the inventory management in the company, specifically focusing on one product as the instance Motor Engine LFTS-2000since it is in the maturity stage of product life cycle. Two scenarios were designed to consider how different parameters affect inventory levels in reverse logistics. The report analysed how different parameters affect the inventory levels and minimum cost. With the increasing returned goods are processed, inventory levels and minimum cost will decrease correspondingly.

Thesis (Ph. D.)--Industrial and Systems Engineering, Georgia Institute of Technology, 2005.
Paul Griffin, Committee Member ; Kwok-Leung Tsui, Committee Chair ; Christos Alexopoulos, Committee Co-Chair ; Hengqing Ye, Committee Co-Chair ; David Goldsman, Committee Member. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Management, Georgia Institute of Technology, 2008.
Committee Chair: Yih-Long Chang; Committee Member: Paul Griffin; Committee Member: Ravi Subramanian; Committee Member: Soumen Ghosh; Committee Member: Srinagesh Gavirneni.

This bachelor thesis is about a stochastic inventory theory and how changes in different parameters affect the cost system. The inventory is based on a stochastic version of an economic quantity order (EOQ) model with planned shortages. For the deterministic EOQ-model with planned shortages there is a convenient formula for optimal order quantity $Q$ minimizing the cost per time unit. For the stochastic version an ($R$,$Q$)-policy is applied where $R$ is a reorder point such that if the inventory level is below $R$ and order is sent and the ordered products arrive after a lead time $L$. Since a formula for the stochastic inventory is not known, optimal choice of $Q$ is numerically obtained by simulations and compared with the optimal $Q$ for the deterministic EOQ with planned shortages. The demand is for simplicity described by a Poisson process. Since having a stochastic inventory model the basic mathematical EOQ formula is inadequate and is replaced with an approximate EOQ formula with planned shortages. By the simulations the accuracy of the EOQ model with planned shortages approximation is investigated and optimal values for some of the  parameters are obtained.

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.
Includes bibliographical references (p. 93-94).
by Dean Harper.
M.S.
M.B.A.

Approved for public release; distribution is unlimited
The Defense Logistics Agency (DLA) predicts issue and receipt workload for its distribution agency in order to maintain adequate staffing levels and set proper rates for customers. Inaccurate forecasts lead to inaccurate staffing, subsequently leading to inaccurate pricing. DLA’s current regression forecasting model is no longer adequate for predicting future workload for DLA Distribution. We explore multiple forecasting techniques and provide a methodology for selecting a model that is a viable and accurate alternative for DLA. Our methodology encompasses best-fit determination, a comparison of predictability through back-casting, and a sensitivity exercise to see reaction and stability of our selected models’ predictions. Finally, we compare our best performing model with the current regression model to see what would have been reported if our model had been used instead of the current model for recent Program Budget Review (PBR) cycles. Our results suggest that an auto-regressive integrated moving average (ARIMA) model used with critical assessment and managerial judgment offers a viable alternative to the current model for predicting distribution workload.

Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, in conjunction with the Leaders for Global Operations Program at MIT, 2018.
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, in conjunction with the Leaders for Global Operations Program at MIT, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 77-79).
The recent surge of direct-to-customer (DTC) orders in the retail industry has increasingly put pressure on omni-channel retailers' supply chain networks to offer faster and cheaper delivery while maintaining their supply chain cost position and committed service level agreements. As warehousing and logistics operations are not part of the core business for most omni-channel retailers, both operations are often outsourced to third-party logistics (3PL) companies. This makes it challenging for omni-retailers to actually improve these operations to handle the surging DTC orders through the relationships with their 3PL partners. This thesis presents cost analysis frameworks for improving the effectiveness of warehousing and logistics cost structures in outsourced omni-channel retail distribution networks. The thesis also conveys short-term and long-term strategy recommendations for reducing supply chain costs of these networks through a case study based on Verizon's retail supply chain network. First, a short-term strategy is proposed through leveraging the key cost drivers identified in a should-cost model developed to simulate receiving, pick-pack, and verification operations in distribution centers (DCs) based on a set of parameter inputs, such as volume, labor rate, labor standard time, facility location, staffing strategy, etc. This zero-based should-cost modeling technique can help the hiring company enhance their bargaining power in contract negotiation with 3PL companies in order to realize cost savings and collaborate on implementing new technologies. Second, a long-term strategy is formed to provide frameworks for omni-channel retailers to reconsider the pros and cons of outsourcing and to think of building sustainable and collaborative relationships with 3PL companies for the coming challenges in the omni-channel retail industry. The recommended execution plan is to stay with a centralized DC model and transition to partnering with capable 3PL service providers to pool ground shipments in order to achieve zone-skipping before the last mile delivery for the future.
by Shile Ding.
M.B.A.
S.M.

To date, closed form optimal solutions for stocking levels in arborescent multiechelon inventory systems have not been obtained. These problems exhibit the joint difficulties of requiring an allocation policy as well as a stocking policy, and the multidimensional nature of their state space makes dynamic programming formulations impractical. In this dissertation, we introduce procedures that approximate multiechelon networks with sets of single installation problems. We first use this technique to solve for base-stock levels in a distribution network with asymmetric retailers. Second, we use this technique to analyze delayed differentiation production processes and provide guidance as to when the strategy is most warranted. Third, we modify the technique to account for inventory that exhibits perishability and solve for stocking policies for distribution systems when the inventory has a fixed shelf life.

Thesis (M.Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.
Includes bibliographical references (leaves 72-73).
by Paritosh Somani.
M.Eng.and S.B.

Dissertation (Ph.D.)--University of Toledo, 2007.
Typescript. "Submitted as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Manufacturing Management." Bibliography: leaves 128-134.

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Systems Science and Industrial Enngineering, 2009.
Includes bibliographical references.

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2009.
Includes bibliographical references (leaf 60).
This thesis presents a framework for deciding which products to centralize in a regional distribution center and which products to store decentralized close to the customer sites, for each facility in a multi-echelon distribution network. Our research specifically focuses on developing an optimization model to determine the inventory positioning strategy that minimizes total costs. The model considers both inbound and outbound transportation costs along with inventory holding costs at all facilities in the network. The total cost and responsiveness of the optimal solution are compared with the baseline network, in which inventory is completely decentralized. Our analysis is performed using several products that have diverse characteristics, in terms of demand patterns, lead-times, product costs, service-level requirements, transportation modes, and supplier locations. A sensitivity analysis is performed to study how a variance in these parameters affects the optimal solution. The research suggests that for high volume commodity items the benefits of centralization are highly dependent upon the degree of lane consolidation. However, for low volume specialty items, centralization can provide immediate benefits with no change to the existing transportation network.
by Deepak Avari and Naman Dayal.
M.Eng.in Logistics

L’environnement concurrentiel des affaires et la mondialisation oblige actuellement les entreprises à accorder une importance particulière à la performance de leur chaîne d’approvisionnement. Afin de se démarquer, les entreprises sont contraintes de prévoir et de gérer des paramètres de performance souvent contradictoires à savoir réduire le coût de leur chaîne d’approvisionnement et augmenter la qualité du service offert à leur clientèle. À cet égard, la planification intégrée de la chaîne logistique c’est-à-dire que les décisions relatives à la l’emplacement des usines, l’approvisionnement, la production, le stockage et la distribution s’avèrent majeures dans le gain d’efficience des entreprises et la réactivité d’une chaîne d’approvisionnement. La production et la planification de la distribution constituent deux opérations fondamentales dans la gestion de la chaîne logistique. Couramment, elles sont traitées de manière distincte du fait de leur complexité. Les coûts d’inventaire sont élevés dans cette approche dite aussi linéaire ou hiérarchique, eu égard à la nécessité de respecter les délais de traitement des commandes et d’assurer la satisfaction des clients. Cependant, il devient impératif de ne plus négliger les liens existants entre les décisions prises pour gérer la production et la distribution, afin de réaliser des économies de coûts dans la chaîne d’approvisionnement. Bien que l’intérêt pour la planification intégrée de chaîne d’approvisionnement soit grandissant, les modèles d’optimisation actuels laissent encore place à l’amélioration afin d’être plus réalistes. Dans cette recherche, nous étudions des problèmes logistiques riches et intégrés. La pertinence de notre apport réside dans l’ajout de variables opérationnelles telles que les fenêtres de temps de service ou la configuration de réseaux flexibles ainsi que de certaines caractéristiques environnementales, dans des modèles logistiques. Notre objectif est de mettre en évidence les valeurs d’intégration, en termes d’économies de coûts et de réduction de gaz à effet de serre. Premièrement, nous décrivons, modélisons et résolvons le problème qui se présent chez un partenaire industriel qui fabrique un seul produit. Dans ce système, la capacité de production et le niveau d’inventaire sont limités, les transferts inter-usines sont permis et les fenêtres de délais de livraison sont flexibles. En nous appuyant sur un vaste ensemble de données réelles collectées chez notre partenaire, nous comparons l’approche intégrée avec plusieurs scénarios de pratique courante. Nous utilisons une méthode exacte qui permet de résoudre chacun des scénarios et étudions les compromis entre les coûts et les niveaux de service dans une analyse de sensibilité détaillée. Les résultats obtenus démontrent ainsi comment l’application d’une approche synchronisée et holistique dans la prise de décision apporte de nombreuses opportunités bénéfiques pour les systèmes logistiques en général. Nous étendons par la suite notre étude aux systèmes de production multi-produits et multiéchelons. Cette nouvelle configuration du problème implique que les produits sont expédiés aux clients par l’intermédiaire d’un ensemble de centres de distribution dont le producteur peut contrôler l’emplacement. Dans cette analyse, la conception de notre réseau de transport est flexible puisqu’il peut varier au cours du temps. Plus le problème est riche et s’approche de la réalité, plus le problème devient difficile et compliqué à résoudre. Les meilleures solutions issues de l’approche intégrée sont obtenues au détriment d’une plus grande complexité d’implémentation et de l’allongement du temps d’exécution. Nous décrivons, modélisons et résolvons le problème en utilisant d’abord des approches de prise de décision intégrées puis des approches séquentielles afin de déterminer à quel le moment l’usage d’une approche plus complexe est avantageuse pour résoudre le problème. Les résultats confirment la pertinence de l’approche intégrée comparativement à l’approche séquentielle. Pour illustrer l’importance des économies réalisées grâce au caractère flexible de la conception de réseaux et des fenêtres de temps de livraison, nous décrivons, modélisons et résolvons un problème de localisation-tournées de vehicules intégré et flexible à deux échelons. Dans ce problème, le fournisseur livre la marchandise à ses clients grâce à un réseau d’approvisionnement à deux échelons, avec une pénalité pour chaque demande non réalisée dans la fenêtre de livraison prédéterminée. La problématique est ici traitée dans une configuration plus riche; la livraison est planifiée en tournées de véhicules. Le quatrième volet de cette thèse s’intéresse aux impacts environnementaux des décisions logistiques. En effet, le plus souvent, les recherches scientifiques sur l’optimisation des chaînes d’approvisionnement se concentrent uniquement sur les aspects économiques du développement durable et tendent à ignorer les deux autres dimensions. Nous abordons donc des problématiques d’optimisation connues sous de nouveaux angles. Nous étudions deux systèmes intégrés de production, d’inventaire, de localisation et de distribution dans lesquels une marchandise produite à une usine est livrée aux détaillants dans un horizon de temps fini. Une analyse de sensibilité élaborée nous permet d’améliorer nos connaissances sur les coûts et les émissions dans les chaînes d’approvisionnement intégrées, en plus d’améliorer notre compréhension des coûts associés à l’implantation de solutions respectueuses de l’environnement. Dans cette thèse, nous visons non seulement une meilleure compréhension de l’approche englobante de logistique intégrée mais nous développons également des outils opérationnels pour son application dans des cas complexes concrets. Nous proposons ainsi de nouveaux modèles d’affaires capables d’améliorer la performance de la chaine d’approvisionnement tout en développant des techniques d’implémentation mathématiques efficaces et efficientes. Mots Clés: Optimisation intégrée, Problème de dimensionnement dynamique de lots, Fenêtres de temps de livraison, Problèmes de localisation, Distribution.
Today’s challenging and competitive global business environment forces companies to place a premium upon the performance of their supply chains. The key to success lies in understanding and managing several contradicting performance metrics. Companies are compelled to keep their supply chain costs low and to maintain the service level high. In this regard, integrated planning of important supply chain decisions such as location, procurement, production, inventory, and distribution has proved to be valuable in gaining efficiency and responsiveness. Two fundamental operations in supply chain management are production and distribution planning. Traditionally, mainly due to the high complexity and difficulty of these operations, they have been treated separately. This hierarchical or sequential decision making approach imposes high inventory holding cost, as in the traditional approach inventory plays an important role in timely satisfying the demand. However, in the era of supply chain cost reduction, it is becoming increasingly apparent that the interrelations between different decisions, and especially production and distribution decisions, can no longer be neglected. Although the research interest in the integrated supply chain planning has been recently growing, there is still much room to further improve and make the existing models more realistic. Throughout this research, we investigate different rich integrated problems. The richness of the models stems from real-world features such as delivery time windows, flexible network designs, and incorporation of environmental concerns. Our purpose is to highlight the values of integration, in terms of cost savings and greenhouse gas emission reduction. First, we describe, model, and solve a plant-customer, single product setting in which production and inventory are capacitated and inter-plant transshipment is allowed. The problem is flexible in terms of delivery due dates to customers, as we define a delivery time window. Using a large real dataset inspired from an industrial partner, we compare the integrated approach with several current practice scenarios. We use an exact method to find the solution of each scenario and study the trade-offs between cost and service level in a detailed sensitivity analysis. Our results indicate how the use of a synchronized and holistic approach to decision making provides abundant opportunities for logistics systems in general. We further extend our study by considering a multi-product and multi-echelon setting. In this problem, products are shipped to customers through a set of distribution centers, and the producer has control over their locations. In this study our network design is flexible since it may change over time. As the problem gets richer and more realistic, it also becomes more complex and difficult to solve. Better solutions from the integrated approach are obtained at the expense of higher implementation complexity and execution time. We describe and model the problem, and solve it with both integrated and sequential decision making approaches to indicate when the use of a more complex approach is beneficial. Our work provides insights on the value of the integrated approach compared to the sequential one. To highlight how the two types of flexibility, from the network design and from the delivery time windows, lead to economic savings, we describe, model, and solve an integrated flexible two-echelon location routing problem. In this problem a supplier delivers a commodity to the customers through a two-echelon supply network. Here, we also consider a penalty for each demand that is not satisfied within the pre-specified time window. The problem is studied in a richer setting, as the distribution is conducted via vehicle routing. The fourth part of this thesis addresses the environmental impacts of logistic decisions. Traditionally, supply chain optimization has merely concentrated on costs or the economic aspects of sustainability, neglecting its environmental and social aspects. Aiming to compare the effect of operational decisions not only on costs but also on greenhouse gas emissions, we reassess some well-known logistic optimization problems under new objectives. We study two integrated systems dealing with production, inventory, and routing decisions, in which a commodity produced at the plant is shipped to the retailers over a finite time horizon. We provide elaborated sensitivity analyses allowing us to gain useful managerial implications on the costs and emissions in integrated supply chains, besides important insights on the cost of being environmentally friendly. In this thesis, we aim not only to better understand the integrated logistics as a whole but also to provide useful operational tools for its exploitation. We propose new business models capable of enhancing supply chain performance while at the same time developing mathematical and technical implementation for its effective and efficient use. Keywords: Integrated optimization; Dynamic lot-sizing; Delivery time window; Location analysis; Distribution

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 87-88). Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xix, 243 p.; also includes graphics (some col.). Includes bibliographical references (p. 237-246). Available online via OhioLINK's ETD Center

Thesis (Ph.D.)--City University of Hong Kong, 2009.
"Submitted to Department of Management Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 80-86)

Thesis (M.S. in Management) Naval Postgraduate School, December 1996.
Thesis advisor(s): Paul J. Fields, Keebom Kang. "December 1996." Includes bibliographical references (p. 77-79). Also available online.

Thesis (M.S. in Management) Naval Postgraduate School, December 1996.
"December 1996." Thesis advisor(s): Paul J. Fields and Keebom Kang. Includes bibliographical references (p. 85-89). Also available online.

Thesis (M.S. in Management) Naval Postgraduate School, December 1994.
Thesis advisor(s): Mark W. Stone, Rebecca J. Adams. "December 1994." Includes bibliographical references. Also available online.

Thesis: Ph. D., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 147-150).
The goal of this thesis is to describe, model, and optimize reverse logistics systems commonly used in the Consumer Electronics industry. The context and motivation for this work stem from a collaboration with an industrial partner, a Fortune 500 company that sells consumer electronics and is one of the top retailers in its sector. The thesis is divided into three parts. In the first part of the thesis we model and analyze the problem of forecasting failures of new products. When a new device is introduced to the market there is limited information available about its failure time distribution since most devices have yet to fail. However, there is extensive failure time data for prior devices, as well as evidence that the failure time distribution for new devices can be forecast from the data for prior devices. In this setting, we propose two strategies for forecasting the failure distribution of new products that leverages the censored failure observations for the new devices as well as this massive amount of data collected for prior devices. We validate these strategies using data from our industrial partner and using data from a social enterprise located in the Boston area. The second part of the thesis concerns inventory management in a reverse logistics system that supports the warranty returns and replacement for a consumer electronic device. This system is a closed-loop supply chain since failed devices are refurbished and are kept in inventory to be used as replacement devices or are sold through a side-sales channel. Furthermore, managing inventory in this system is challenging due to the short life-cycle of this type of device and the rapidly declining value for the inventory that could potentially be sold. We propose a stochastic model that captures the dynamics of inventory of this system, including the limited life-cycle and the declining value of inventory that can be sold off. We characterize the structure of the optimal policy for this problem. In addition, we introduce two heuristics: (i) a certainty-equivalent approximation, which leads to a simple closed form policy; and (ii) a dual balancing heuristic, which results in a more tractable newsvendor type model. We also develop a robust version of this model in order to obtain bounds for the overall performance of the system. The performance of these heuristics is analyzed using data from our industrial partner. The final part of the thesis concerns the problem faced by a consumer electronics retailer when matching devices in inventory to customers. More specifically, we analyze a setting where there are two warranties in place: (i) the consumer warranty, offered by the retailer to the consumer, and (ii) the Original Equipment Manufacturer (OEM) warranty, offered by the OEM to the retailer. Both warranties are valid for a limited period (usually 12 months), and once warranties expire, the coverage to replace or repair a faulty device ends. Thus, a customer does not receive a replacement if he/she is out of consumer warranty, and the retailer cannot send the device to the OEM for repairs if it is out of OEM warranty. The retailer would ideally like to have the two warranties for a device being matched, i.e., the customer would have the same time left in his consumer warranty as the device would have left in the OEM warranty. A mismatch between these warranties can incur costs to the retailer beyond the usual processing costs of warranty requests. Namely, since a device can fail multiple times during its lifecycle the replacement device sent to customers that file warranty requests can lead to out-of-OEM-warranty returns. In order to mitigate the number of out-of-OEM-warranty returns, we propose an online algorithm to match customers that have filed warranty claims to refurbished devices in inventory. The algorithm matches the oldest devices in inventory to the oldest customers in each period. We characterize the competitive ratio of this algorithm and, through numerical experiments using historical data, demonstrate that it can significantly reduce out of warranty returns compared to our partner's current strategy.
by Andre du Pin Calmon.
Ph. D.

One of the key challenges for a modern day health care provider is to dispense high quality of medical care while limiting or even reducing the health care expenditures. This research work endeavours to meet this challenge through effective management of hospitals logistics systems. The aim of this research work is to provide a structured mechanism for modelling and analysing health care logistics to be able to understand its dynamic behaviour and effectively manage its logistical activities on the basis of the model. In order to achieve the research objectives, this research uses system dynamics as the main medium of analysis, and in particular, employs an integrated system dynamics framework which has been used previously for manufacturing industry supply chain designs and tests the feasibility of the framework for analysing and modelling health care logistics. This is ascertained by developing and incorporating a decision making metrics in the system dynamics model based on item criticality, usage, and value to optimise overall logistics costs. System Dynamics methodology is employed at first to develop a model for existing inventory control decisions, and subsequently to produce two alternative approaches based on traditional (R, s, S) inventory control approach and Continuous Replenishment Inventory and Order Based Production Control CR(IOBPCS) approach. These approaches are tested for two case hospitals, namely: Children's National Medical Center (CNMC) USA, and Derbyshire Royal Infirmary (DRI) UK. The dynamic analysis for each case revealed problems in terms of multistage inventories and order batching, which could lead to demand amplification causing a detrimental effect on the inventory management throughout the supply chain. Accordingly, the simulations results produced for the two cases are benchmarked using alternative strategies in terms of lower inventory cost, and robustness to meet the unpredictable demand arising from a large number of items. Overall, this research work has enhanced the understanding of hospitals logistics systems by building qualitative and quantitative models. More specifically, this research work has illustrated the applicability of the integrated system dynamics framework in analysing and modelling hospitals logistics systems and inventory control decisions. One particular contribution of this study is introducing inventory classification based on the criticality of items for patient needs which is more suited for health care situations rather purely cost based policies prevalent in other manufacturing and service chains. Therefore, this work has rigorously tested a multi-criteria based inventory classification method that takes into account the criticality of use, cost, and usage value of items for optimising overall inventory cost while maintaining the required patient care/service level. Future studies may be conducted to further evaluate the trade-offs in between different logistics decision making (such as, inventory control, service level, purchasing, transportation and warehousing) in order to design a set of "best practice" simulation models to optimise the overall dynamic behaviour for health care supply chains.

To become a successful company today all costs, must be kept to a minimum. To make sure they are companies need to try new methods and policies to get closer to an optimum production. One of the things that need attention is the inventory of spare parts and the replacement of the same. The companies want their machines to have as many active hours as possible and therefore they need to replace components in them from time to time. This study will compare the current policy with a new one to see if it is economically justifiable to minimize the inventory of spare parts. This will be done by replacing two identical components in the same machine before they fail and production stops. We call it the proactive block replacement policy. To test this new policy a simulation based on historical data was made where the costs associated with the different replacements such as cost of component, cost o lost production and cost of the two types of replacements. All these costs were considered to see is the company could save money through this change. The result showed that the new policy was not suitable for this specific component because the cost of the component and the variation of lifetime on it was too high. Because of the big variation of lifetime, the time of the replacement had to be set after fewer hours of production which means more components will be used and the cost per active hour will be higher. This study is limited because only one specific component at a specific machine was studied and it is not possible to make any assumptions for other components from this study. This had to be done to get the most precise information from the company to get the best result. The conclusion of this study is that the company should keep their current replacement theory and not change into the new one. Though there might be possible ways of lowering the costs by only having one component in inventory instead of two.
För att bli ett framgångsrikt företag i dagens samhälle måste alla kostnader hållas till ett minimum. För att försäkra sig om detta måste företagen försöka hitta nya metoder och strategier för att komma närmare en optimal produktion. En av de saker som behöver undersökas är lagerhållningen av reservdelar och byten av de samma. Företagen vill att deras maskiner ska ha så många aktiva timmar som möjligt och därför behöver de ersätta komponenter i dem ibland. Denna undersökning kommer att jämföra den nuvarande strategin med en ny för att se om det är ekonomiskt fördelaktigt att minimera lagret av reservdelar. Detta görs genom att byta två identiska komponenter i samma maskin innan de hinner gå sönder och produktionen stannar. Vi kallar det för den proaktiva blockersättningspolicyn. För att testa den nya strategin gjordes en simulering baserad på historiska data där kostnaderna förknippade med de olika bytena, som till exempel komponentkostnad, kostnader och förlorad produktion och kostnad för de två typerna av byten. Alla dessa kostnader användes för att se om företaget kunde spara pengar genom att byta strategi. Resultatet visade att den nya strategin inte var lämplig för den specifika komponenten eftersom kostnaden för komponenten och variationen i livstiden, var för hög. På grund av den stora variationen i livslängden måste tiden för bytet planeras in efter färre timmars produktion, vilket betyder att fler komponenter kommer behöva köpas in och kostnaden per aktiv timme blir högre. Denna studie är avgränsad på så vis att endast en specifik komponent, på en specifik maskin, har studerats och det är inte möjligt att göra några generella antaganden för andra komponenter utifrån denna studie. För att få rättvisa och exakta resultat valdes att endast en komponent skulle undersökas för bästa resultat. Slutsatsen av denna studie är att företaget bör behålla sin nuvarande strategi för byten av komponenter och inte förändra till den nya. Trots detta kan det finnas möjliga sätt att sänka kostnaderna genom att bara ha en komponent i lager istället för två.