Logistics makes extensive use of human and material resources to achieve a target level of customer service at the lowest possible cost. It has been recognized as a major key to success in commerce and industry, and continues to evolve radically and grow in importance in recent years. Warehousing, as one of the most costly elements of logistics, is often the central operation in most logistics networks. Its successful management is critical in terms of both cost and service. In this thesis, two problem areas in warehouse logistics are studied: stock loading and order picking. Stock loading is an essential operation in modern logistics. Improvement on container capacity utilization and loading efficiency significantly reduces costs. For a given set of boxes in different sizes and an unlimited number of identical containers, the basic cargo loading problem is to determine the minimum number of containers required. The problem is proven NP-hard. To tackle this problem, a Tabu search optimization with a tree-based cargo loading algorithm as its inner heuristic is proposed. This approach has flexibility in taking different box conditions into consideration, and can find better solutions on average than other recent meta- or heuristic algorithms. Decreasing order sizes and increasing fuel costs provide a strong incentive for the inner-city truck loading operation to utilize container space more efficiently in transporting goods to multiple clients during one trip. This considers not only traditional loading constraints, but also multi-drop requirements. A wallbuilding heuristics based on a binary tree data structure is proposed to handle these side constraints. A dynamic space decomposition approach, together with a repacking and space amalgamation strategy, permits an efficient and effective loading plan. Order picking, one of the most critical warehousing operations, is the second problem studied in this thesis. An analytical approximation model is proposed based on probability modeling and queueing network theory applied to a synchronized zone picker-to-part order picking system with different routing and ABC-class inventory storage policies. The numerical results are compared and validated via simulation. The resulting model can therefore be usefully applied in the design and selection process of order picking systems. The routing versus storage issues are further investigated with a simulation model. This extends the existing research by evaluating multiple routing and storage policies under varying operating conditions. Results show that the midpoint, return and traversal routing policies generally perform best when paired with perimeter, across-aisle and within-aisle storage strategies, respectively. Yet performance is indeed dependent on demand patterns, zone sizes, batch sizes and order sizes. At first glance, order picking and stock loading operation seem to pursue different objectives. However, they are two related operations conducted sequentially from internal to the outbound side of warehousing. An efficient order picking system is a precondition for an effective loading operation at the shipping dock, especially when multiple orders need to be selected for consolidation in shipment. The proposed loading algorithms and the order picking system performance evaluation models can be used to further study the effective integration of these two functions. / published_or_final_version / Mathematics / Doctoral / Doctor of Philosophy

Supplier selection and order allocation are significant decisions for a manufacturer to ensure stable material flows in a highly competitive supply chain, in particular when customers are willing to accept products with less desirable product attributes. Hence, this study develops efficient methodologies to solve optimally the integrated supplier selection and order allocation problem incorporating customer flexibility for a manufacturer producing multiple products over a multi-period planning horizon. In this research, a new fuzzy multi-attribute approach is proposed to evaluate customer flexibility which is characterized through range and response. The approach calculates the product’s general utility value. This value is used by a bi-variant function which is developed to determine the retail price for the product. A new mixed integer program model describing the behavior of the basic problem is firstly developed. This basic model is the first to jointly determine: 1) type and quantity of the product variants to be offered; 2) the suppliers to be selected and orders to be allocated; and 3) inventory levels of product variants and raw materials/components. The objective is to maximize the manufacturer’s total profit subject to various operating constraints. This basic problem constitutes a very complex combinatorial optimization problem that is Nondeterministic Polynomial (NP)-hard. To tackle this challenge, two new optimization algorithms, i.e., an improved genetic approach called king GA (KGA) and an innovative hybrid algorithm called (CP-SA) _I which combines the techniques of constraint programming and simulated annealing are developed to locate optimal solutions. Extensive computational experiments demonstrate the effectiveness of these algorithms and also show clearly that (CP-SA) _I outperforms KGA in terms of both solution quality and computational cost. To examine the influence of subcontracting as one widespread practice in modern production management, this study also develops a modified mathematical model. It shares some similarity with the basic model but brings additional complexity by taking into consideration subcontractors for inter-mediate components and machine capacity. Since (CP-SA) _I outperforms KGA, it is employed and modified to solve the modified problem. Hence, this study presents a new hybrid algorithm called (CP-SA) _II, to locate optimal solutions. This study also establishes a new parallel (CP-SA) _II algorithm to enhance the performance of (CP-SA) _II. This parallel algorithm is implemented on a distributed computing platform based on the contemporary Graphic Processing Unit (GPU) using the Compute Unified Device Architecture (CUDA) programming model. Extensive numerical experiments conducted clearly demonstrate that the parallel (CP-SA) _II algorithm and its serial counterpart are efficient and robust optimization tools for formulating integrated supplier selection and order allocation decisions. Sensitivity analysis is employed to study the effects of the critical parameters on the performance of these algorithms. Finally, the convergence behavior of the proposed parallel (CP-SA) _II algorithm is studied theoretically. The results prove that the search process eventually converges to the global optimum if the overall best solution is maintained over time. / published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 97-100. / M.S.

Finally, we study a multi-period, risk-averse inventory model. The objective is to maximize the expected pay-offs. The risk-averse behavior is modeled as to penalize the decision maker if a target-profit level is not satisfied for each financial reporting cycle. We recognize that the operational period is usually faster than the financial reporting cycle. Therefore, the financial reporting cycle can be considered as an integer times of the operational periods. We study this model under both accrual-basis accounting principle and cash-basis accounting principle. We prove that the optimal inventory policy is a state-dependent base-stock policy under the accrual-basis accounting method. We then show that the structure of an optimal policy is a complicated one for the cash-basis accounting method. / In this thesis we study three supply chain models which address downside risk from a different angle. We start with a commitment-option supply contract in a Conditional Value-at-Risk (CVaR) framework. We show that a CVaR trade-off analysis with advanced reservation can be carried out efficiently. Moreover, our study indicates how the corresponding contract decisions differ from decisions for optimizing an expected value. / Key words. Downside Risk Measure; CVaR; Risk; Loss-Averse; Dynamic Programming. / Owing to the growing globalization in economy and the advances in commerce, research in supply chain management has attracted large number of researchers in the last two decades. Yet standard treatments of supply chain models are mainly confined for the optimization of expected values with little reflection on risk considerations. Even for those that consider a risk measure in the objective function, there are quite few literatures employing downside risk measure. The downside risk measure takes into account only the part of the distribution that is below a critical value. Thus it indicates a safety-first strategy for decision maker. / The thesis is organized in five chapters. In Chapter 1, we provide the background and research motivation for considering downside risk measures in supply chain models. In Chapter 2, we study the pay-to-delay supply contracts with a Conditional Value-at-Risk (CVaR) framework. In Chapter 3, we study the loss-averse newsvendor problem. In Chapter 4, we extend the loss-averse model to a multi-period setting. We conclude the thesis in Chapter 5 with discussions for future research. / Then, we employ a loss-aversion utility function to characterize newsvendor's decision-making behavior. We find that when there is no shortage cost, the loss-averse newsvendor consistently orders less than a risk-neutral newsvendor. Further, we discover that the loss-averse newsvendor orders a constant quantity when the reference target is sufficiently large. We discuss the importance of initial inventory to achieve the target profit level. When the target is a decision variable, the newsvendor always sets the target no higher or no lower. / Ma, Lijun. / "October 2007." / Adviser: Houmin Yan. / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 5003. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 140-154). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Chen, Chen. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (p. 89-94). / Abstracts in English and Chinese. / Table of Contents --- p.vi / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Literature Review --- p.6 / Chapter 2.1 --- Operations and Finance Interface --- p.6 / Chapter 2.1.1 --- Single Period Setting --- p.6 / Chapter 2.1.2 --- Multi-Period Setting --- p.11 / Chapter 2.2 --- Trade Credit --- p.13 / Chapter 2.3 --- Supply Chain Contracts --- p.14 / Chapter 3 --- The Model --- p.16 / Chapter 3.1 --- Model Description --- p.16 / Chapter 3.1.1 --- The Basic Setting --- p.17 / Chapter 3.1.2 --- The Bank Loan Setting --- p.19 / Chapter 3.1.3 --- The Trade Credit Setting --- p.19 / Chapter 3.2 --- Demand Distribution Properties --- p.22 / Chapter 4 --- Retailer's Perspective --- p.24 / Chapter 4.1 --- The Single Period Problem --- p.24 / Chapter 4.2 --- The Basic Setting --- p.33 / Chapter 4.3 --- The Bank Loan Setting --- p.37 / Chapter 4.4 --- The Trade Credit Setting --- p.43 / Chapter 4.5 --- Summary --- p.47 / Chapter 5 --- Supplier's Perspective --- p.48 / Chapter 5.1 --- Single Period Results --- p.48 / Chapter 5.1.1 --- The Basic Setting --- p.49 / Chapter 5.1.2 --- The Bank Loan Setting --- p.53 / Chapter 5.1.3 --- The Trade Credit Setting --- p.60 / Chapter 5.2 --- Two-Period Problem --- p.69 / Chapter 5.3 --- Summary --- p.71 / Chapter 6 --- Numerical Study and Insights --- p.72 / Chapter 6.1 --- The Single Period Supply Chain --- p.72 / Chapter 6.1.1 --- Impact of Different Financing Schemes --- p.73 / Chapter 6.1.2 --- Supply Chain Efficiency --- p.77 / Chapter 6.2 --- Capital Constrained Retailer in Two-Period Setting --- p.79 / Chapter 6.2.1 --- Impacts of Different Financial Schemes on the Retailer --- p.79 / Chapter 6.2.2 --- Saving for the Future --- p.82 / Chapter 6.2.3 --- Comparison of the Single- and Two-Period Settings --- p.83 / Chapter 7 --- Conclusion and Future Research --- p.84 / Appendix / A Log-concavity of Some Common Distributions --- p.87 / Bibliography --- p.89

published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

The integration of production and distribution decisions presents a challenging problem for manufacturers trying to optimize their supply chain. At the planning level, the immediate goal is to coordinate production, inventory, and delivery to meet customer demand so that the corresponding costs are minimized. Achieving this goal provides the foundations for streamlining the logistics network and for integrating other operational and financial components of the system. In this paper, a model is presented that includes a single production facility, a set of customers with time varying demand, a finite planning horizon, and a fleet of vehicles for making the deliveries. Demand can be satisfied from either inventory held at the customer sites or from daily product distribution. A procedure centering on a reactive tabu search is developed for solving the full problem. After a solution is found, path relinking is applied to improve the results. A novel feature of the methodology is the use of an allocation model in the form of a mixed integer program to find good feasible solutions that serve as starting points for the tabu search. Lower bounds on the optimum are obtained by solving a modified version of the allocation model. Computational testing on a set of 90 benchmark instances with up to 200 customers and 20 time periods demonstrates the effectiveness of the approach. In all cases, improvements ranging from 10 - 20% were realized when compared to those obtained from an existing greedy randomized adaptive search procedure (GRASP). This often came at a three- to five-fold increase in runtime, however. A hybrid scheme that combines the features of reactive tabu search algorithm and branch-and-price algorithm is also developed. The combined approach takes advantage of the efficiency of the tabu search heuristic and the precision of the branch-and-price algorithm. Branching strategy that is suitable for the problem is proposed. Several advance techniques such as column generation heuristic and rounding heuristic are also implemented to improve the efficiency of the algorithm. Computational testing on standard data sets shows that a hybrid algorithm can practically solve instances with up to 50 customers and 8 time periods which is not possible by standard branch-and-price algorithm alone. / text

Often, in both the military and industrial sectors, the unavailability of essential components renders a complex system inoperable. Therefore, the primary objective of this research is to develop a methodology for determination of feasible strategies for the repair/replace decision. In the general equipment replacement problem, a finite planning horizon may be partitioned into stages such that an end item deteriorates toward a final stage where it is no longer economically or operationally feasible to continue to repair the item, or the item experiences fatal failure. This multi-stage deterioration process is very amenable to a dynamic programming solution methodology where the output from one stage becomes the input to the next stage. In the multi-stream replacement problem, the population of end items is grouped into streams depending upon such parameters as item age, the number of operational hours, or the environment in which the item operates. The reliability function is used to describe the survivor probability in this population model. A dynamic repair/replace program is formulated where the state functions are characterized by two parameters - item age and current operational condition. A computerized model is then developed that facilitates evaluation of repair/replacement strategies with respect to total life cycle costs of a logistics system. The solution methodology accommodates both stochastic and/or deterministic demand; different hazard models; a budget constraint; repair capacity constraint; various levels of repair; technological improvement; and organizational implementation issues. The operations impact of a generalized methodology for supporting the repair/replace decision and mode of repair is to provide opportunities for a more efficient use of organizational resources such as capital and repair facilities. / Ph. D. / incomplete_metadata

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The (classical) domination number of a graph is the cardinality of a smallest subset of its vertex set with the property that each vertex of the graph is in the subset or adjacent to a vertex in the subset. Since its introduction to the literature during the early 1960s, this graph parameter has been researched extensively and nds application in the generic facility location problem where a smallest number of facilities must be located on the vertices of the graph, at most one facility per vertex, so that there is at least one facility in the closed neighbourhood of each vertex of the graph. The placement constraint in the above application may be relaxed in the sense that multiple facilities may possibly be located at a vertex of the graph and the adjacency criterion may be strengthened in the sense that a graph vertex may possibly be required to be adjacent to multiple facilities. More speci cally, the number of facilities that can possibly be located at the i-th vertex of the graph may be restricted to at most ri 0 and it may be required that there should be at least si 0 facilities in the closed neighbourhood of this vertex. If the graph has n vertices, then these restriction and su ciency speci cations give rise to a pair of vectors r = [r1,....., rn] and s = [s1,....., sn]. The smallest number of facilities that can be located on the vertices of a graph satisfying these generalised placement conditions is called the hr; si-domination number of the graph. The classical domination number of a graph is therefore its hr; si-domination number in the special case where r = [1,....., 1] and s = [1,....., 1]. The exact values of the hr; si-domination number, or at least upper bounds on the hr; si- domination number, are established analytically in this dissertation for arbitrary graphs and various special graph classes in the general case, in the case where the vector s is a step function and in the balanced case where r = [r,....., r] and s = [s,....., s]. A linear algorithm is put forward for computing the hr; si-domination number of a tree, and two exponential-time (but polynomial-space) algorithms are designed for computing the hr; si- domination number of an arbitrary graph. The e ciencies of these algorithms are compared to one another and to that of an integer programming approach toward computing the hr; si- domination number of a graph. / AFRIKAANSE OPSOMMING: Die (klassieke) dominasiegetal van 'n gra ek is die grootte van 'n kleinste deelversameling van die gra ek se puntversameling met die eienskap dat elke punt van die gra ek in die deelversameling is of naasliggend is aan 'n punt in die deelversameling. Sedert die verskyning van hierdie gra ekparameter in the literatuur gedurende die vroeë 1960s, is dit deeglik nagevors en vind dit neerslag in die generiese plasingstoepassing waar 'n kleinste getal fasiliteite op die punte van die gra ek geplaas moet word, hoogstens een fasiliteit per punt, sodat daar minstens een fasiliteit in die geslote buurpuntversameling van elke punt van die gra ek is. Die plasingsbeperking in die bogenoemde toepassing mag egter verslap word in die sin dat meer as een fasiliteit potensieel op 'n punt van die gra ek geplaas kan word en verder mag die naasliggendheidsvereiste verhoog word in die sin dat 'n punt van die gra ek moontlik aan veelvuldige fasiliteite naasliggend moet wees. Gestel dat die getal fasiliteite wat op die i-de punt van die gra ek geplaas mag word, beperk word tot hoogstens ri 0 en dat hierdie punt minstens si 0 fasiliteite in die geslote buurpuntversameling daarvan moet hê. Indien die gra ek n punte bevat, gee hierdie plasingsbeperkings en -vereistes aanleiding tot die paar vektore r = [r1, .... , rn] en s = [s1,...., sn]. Die kleinste getal fasiliteite wat op die punte van 'n gra ek geplaas kan word om aan hierdie veralgemeende voorwaardes te voldoen, word die hr; si-dominasiegetal van die gra ek genoem. Die klassieke dominasiegetal van 'n gra ek is dus die hr; si-dominasiegetal daarvan in die spesiale geval waar r = [1,......, 1] en s = [1,....., 1]. In hierdie verhandeling word die eksakte waardes van, of minstens grense op, die hr; si-dominasiegetal van arbitrêre gra eke of spesiale klasse gra eke analities bepaal vir die algemene geval, vir die geval waar s 'n trapfunksie is, en vir die gebalanseerde geval waar r = [r,....., r] en s = [s,....., s]. 'n Lineêre algoritme word ook daargestel vir die berekening van die hr; si-dominasiegetal van 'n boom, en twee eksponensiële-tyd (maar polinoom-ruimte) algoritmes word ontwerp vir die berekening van die hr; si-dominasiegetal van 'n arbitrêre gra ek. Die doeltre endhede van hierdie algoritmes word met mekaar vergelyk en ook met dié van 'n heeltallige programmeringsbenadering tot die bepaling van die hr; si-dominasiegetal van 'n gra ek.

Ce projet de recherche s’inscrit dans un partenariat entre l’ANDRA (Agence Nationale pour la gestion des Déchets Radioactifs) et le LOSI de l’Institut Charles Delaunay (STMR UMR CNRS), UTT.La thèse vise à dimensionner les ouvrages de stockage vis-à-vis des divers flux industriels. Les flux concernés sont de nature variée et cela constitue l’une des caractéristiques du stockage. Les ouvrages doivent en effet être conçus pour permettre un développement progressif, à l’origine d’une coexistence de flux nucléaires (les colis de déchets nucléaires et les flux associés, telle la ventilation nucléaire) et de flux de chantiers conventionnels. Le dimensionnement des flux et la conception des ouvrages pour autoriser ces flux se trouvent donc au cœur du processus de conception du stockage.La problématique de notre partenaire industriel porte sur la conception de réseau (appelé flow path design). Notre contribution est dédiée au développement de modèles de flow path design avec de nouvelles contraintes ainsi qu’au développement de méthodes. Les extensions au modèle de base prennent en compte une flotte hétérogène, des segments interdits d’accès à certains véhicules et des coûts de construction. Différentes méthodes d'optimisation approchées ont aussi été développées et testées. Il s’agit de métaheuristiques basées sur les recherches locales, l’algorithme de colonies de fourmis ainsi que l’algorithme des abeilles. L’efficacité des méthodes est prouvée grâce à des tests sur des instances de la littérature et l’application au cas réel est faite par simulation / This research project is part of a partnership between ANDRA (National Agency for Radioactive Waste Management) and the LOSI, Institut Charles Delaunay (TSR UMR CNRS), UTT.The thesis aims to design the storage structures for various industrial flows. Flows involved are varied in nature and it is one of the characteristics of the storage. The works must be designed to effect a gradual development, from a "coactivity", that is to say, a coexistence of nuclear flux (the nuclear waste packages and the associated flow, such nuclear ventilation) and conventional flow sites. The design flow and the design of structures to allow these flows are therefore at the heart of the design process of storage.The problem of our industrial partner focuses on flow path design. Our contribution is dedicated to the development of models of flow path design with new constraints and the development of methods. Extensions to the basic model takes into account different type of vehicle, not allowed some segments and taking into account construction costs. Different optimization methods have also been developed and tested. Metaheuristics are based on local search, the ant colony algorithm and the algorithm of bees. Efficiency of methods is demonstrated through tests on literature benchmarks and application to the real case is done by simulation