255 research outputs found
The multi-handler knapsack problem under uncertainty
The Multi-Handler Knapsack Problem under Uncertainty is a new stochastic knapsack problem where, given a set of items, characterized by volume and random profit, and a set of potential handlers, we want to find a subset of items which maximizes the expected total profit. The item profit is given by the sum of a deterministic profit plus a stochastic profit due to the random handling costs of the handlers. On the contrary of other stochastic problems in the literature, the probability distribution of the stochastic profit is unknown. By using the asymptotic theory of extreme values, a deterministic approximation for the stochastic problem is derived. The accuracy of such a deterministic approximation is tested against the two-stage with fixed recourse formulation of the problem. Very promising results are obtained on a large set of instances in negligible computing time
Container Loading Problems: A State-of-the-Art Review
Container loading is a pivotal function for operating supply chains efficiently. Underperformance results in unnecessary costs (e.g. cost of additional containers to be shipped) and in an unsatisfactory customer service (e.g. violation of deadlines agreed to or set by clients). Thus, it is not surprising that container loading problems have been dealt with frequently in the operations research literature. It has been claimed though that the proposed approaches are of limited practical value since they do not pay enough attention to constraints encountered in practice.In this paper, a review of the state-of-the-art in the field of container loading will be given. We will identify factors which - from a practical point of view - need to be considered when dealing with container loading problems and we will analyze whether and how these factors are represented in methods for the solution of such problems. Modeling approaches, as well as exact and heuristic algorithms will be reviewed. This will allow for assessing the practical relevance of the research which has been carried out in the field. We will also mention several issues which have not been dealt with satisfactorily so far and give an outlook on future research opportunities
Model and Algorithm for Container Allocation Problem with Random Freight Demands in Synchromodal Transportation
This paper aims to investigate container allocation problem with random freight demands in synchromodal transportation network from container carriersā perspective. Firstly, the problem is formulated as a stochastic integer programming model where the overall objective is to determine a container capacity allocation plan at operational level, so that the expected total transportation profit is maximized. Furthermore, by integrating simulated annealing with genetic algorithm, a problem-oriented hybrid algorithm with a novel gene encode method is designed to solve the optimization model. Some numerical experiments are carried out to demonstrate the effectiveness and efficiency of the proposed model and algorithm
Mathematical models and heuristic algorithms for routing problems with multiple interacting components.
Programa de P?s-Gradua??o em Ci?ncia da Computa??o. Departamento de Ci?ncia da Computa??o, Instituto de Ci?ncias Exatas e Biol?gicas, Universidade Federal de Ouro Preto.Muitos problemas de otimiza??o com aplica??es reais t?m v?rios componentes de intera??o. Cada um deles pode ser um problema pertencente ? classe N P-dif?cil, e eles podem estar em conflito um com o outro, ou seja, a solu??o ?tima para um componente n?o representa necessariamente uma solu??o ?tima para os outros componentes. Isso pode ser um desafio devido ? influ?ncia que cada componente tem na qualidade geral da solu??o. Neste trabalho, foram abordados quatro problemas de roteamento complexos com v?rios componentes de intera??o: o Double Vehicle Routing Problem with Multiple Stacks (DVRPMS), o Double Traveling Salesman Problem with Partial Last-InFirst-Out Loading Constraints (DTSPPL), o Traveling Thief Problem (TTP) e Thief Orienteering Problem (ThOP). Enquanto os DVRPMS e TTP j? s?o bem conhecidos na literatura, os DTSPPL e ThOP foram recentemente propostos a fim de introduzir e estudar variantes mais realistas dos DVRPMS e TTP, respectivamente. O DTSPPL foi proposto a partir deste trabalho, enquanto o ThOP foi proposto de forma independente. Neste trabalho s?o propostos modelos matem?ticos e/ou algoritmos heur?sticos para a solu??o desses problemas. Dentre os resultados alcan?ados, ? poss?vel destacar que o modelo matem?tico proposto para o DVRPMS foi capaz de encontrar inconsist?ncias nos resultados dos algoritmos exatos previamente propostos na literatura. Al?m disso, conquistamos o primeiro e o segundo lugares em duas recentes competi??es de otimiza??o combinat?ria que tinha como objetivo a solu??o de uma vers?o bi-objetiva do TTP. Em geral, os resultados alcan?ados por nossos m?todos de solu??es mostraram-se melhores do que os apresentados anteriormente na literatura considerando cada problema investigado neste trabalho.I would like to express my greatest thanks to my parents, Jo?o Batista and Adelma, and my sister, Jaqueline, for their wise counsel. They have always supported me and given me the strength to continue towards my goals. To Bruna Vilela, I am grateful for her fondness, for always listening to my complaints, and for celebrating with me my personal and academic achievements. I love you all demais da conta1 ! Throughout the writing of this thesis, I have received great assistance. I would like to acknowledge my advisors, Prof. Ph.D. Marcone J. F. Souza, and Prof. Ph.D. Andr? G. Santos, for their support and guidance over these years. I would also like to thank all the authors who have contributed to the research papers produced from this work, in particular, to Prof. Ph.D. Markus Wagner for his great collaboration in some of my projects. I would like to thank Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES), and Universidade Federal de Ouro Preto (UFOP) for funding this project. I thank the Universidade Federal de Vi?osa (UFV) for receiving me as a collaborating researcher over these last two years. I could not but offer up my thanks to the HassoPlattner-Institut (HPI) Future SOC Lab, the Divis?o de Suporte ao Desenvolvimento Cient?fico e Tecnol?gico (DCT/UFV), and the Programa de P?s-gradua??o em Ci?ncia da Computa??o (PPGCC/UFOP) for enabling this research by providing access to their computing infrastructure
The Air Cargo Load Planning Problem
A major operational planning problem in the air cargo industry is how to arrange cargo
in an aircraft to fly safely and profitably. Therefore, a challenging planning puzzle has to
be solved for each flight. Besides its complexity, the planning is mostly done manually
today, which is a time consuming process with uncertain solution quality. The literature
on loading problems in an air cargo context is scarce and the term is used ambiguously for
different subproblems like selecting containers, packing items into containers, or loading
containers into aircraft. All of the presented models only focus on certain aspects of what
is in practice a larger planning problem. Additionally, some practical aspects have not
been covered in the literature.
In this work, we provide a comprehensive overview of the air cargo load planning problem
as seen in the operational practice of our industrial partner. We formalize its requirements
and the objectives of the respective stakeholders. Furthermore, we develop and
evaluate suitable solution approaches. Therefore, we decompose the problem into four
steps: aircraft configuration, build-up scheduling, air cargo palletization, and weight and
balance. We solve these steps by employing mainly mixed-integer linear programming.
Two subproblems are further decomposed by adding a rolling horizon planning approach
and a Logic-based Benders Decomposition (LBBD). The actual three-dimensional packing
problem is solved as a constraint program in the subproblem of the LBBD.
We evaluated our approaches on instances containing 513 real and synthetic flights. The
numerical results show that the developed approaches are suitable to automatically generate
load plans for cargo flights. Compared to load plans from practice, we could achieve
a 20 percent higher packing density and significantly reduce the handling effort in the air
cargo terminal. The achieved costs of additional fuel burn due to aircraft imbalances and
reloading operations at stop-over airports are almost negligible. The required runtimes
range between 13 and 38 minutes per flight on standard hardware, which is acceptable
for non-interactive planning.
Cargo airlines can significantly profit from employing the developed approaches in their
operational practice. More and especially the profitable last-minute cargo can be transported.
Furthermore, the costs of load planning, handling effort, and aircraft operations
can be significantly reduced
ProbleĢmes de tourneĢes de veĢhicules avec contraintes de chargement
Cette theĢse sāinteĢresse aux probleĢmes de tourneĢes de veĢhicules ouĢ lāon retrouve des contraintes de chargement ayant un impact sur les seĢquences de livraisons permises. Plus particulieĢrement, les items placeĢs dans lāespace de chargement dāun veĢhicule doivent eĢtre directement accessibles lors de leur livraison sans quāil soit neĢcessaire de deĢplacer dāautres items. Ces probleĢmes sont rencontreĢs dans plusieurs entreprises de transport qui livrent de gros objets (meubles, eĢlectromeĢnagers).
Le premier article de cette theĢse porte sur une meĢthode exacte pour un probleĢme de confection dāune seule tourneĢe ouĢ un veĢhicule, dont lāaire de chargement est diviseĢe en un certain nombre de piles, doit effectuer des cueillettes et des livraisons respectant une contrainte de type dernier entreĢ, premier sorti. Lors dāune collecte, les items recueillis doivent neĢcessairement eĢtre deĢposeĢs sur le dessus de lāune des piles. Par ailleurs, lors dāune livraison, les items doivent neĢcessairement se trouver sur le dessus de lāune des piles. Une meĢthode de seĢparation et eĢvaluation avec plans seĢcants est proposeĢe pour reĢsoudre ce probleĢme.
Le second article preĢsente une meĢthode de reĢsolution exacte, eĢgalement de type seĢparation et eĢvaluation avec plans seĢcants, pour un probleĢme de tourneĢes de veĢhicules avec chargement dāitems rectangulaires en deux dimensions. Lāaire de chargement des veĢhicules correspond aussi aĢ un espace rectangulaire avec une orientation, puisque les items doivent eĢtre chargeĢs et deĢchargeĢs par lāun des coĢteĢs. Une contrainte impose que les items dāun client soient directement accessibles au moment de leur livraison.
Le dernier article aborde une probleĢme de tourneĢes de veĢhicules avec chargement dāitems rectangulaires, mais ouĢ les dimensions de certains items ne sont pas connus avec certitude lors de la planification des tourneĢes. Il est toutefois possible dāassocier une distribution de probabiliteĢs discreĢte sur les dimensions possibles de ces items. Le probleĢme est reĢsolu de manieĢre exacte avec la meĢthode L-Shape en nombres entiers.In this thesis, we study mixed vehicle routing and loading problems where a constraint is imposed on delivery sequences. More precisely, the items in the loading area of a vehicle must be directly accessible, without moving any other item, at delivery time. These problems are often found in the transportation of large objects (furniture, appliances).
The first paper proposes a branch-and-cut algorithm for a variant of the single vehicle pickup and delivery problem, where the loading area of the vehicle is divided into several stacks. When an item is picked up, it must be placed on the top of one of these stacks. Conversely, an item must be on the top of one of these stacks to be delivered. This requirement is called āLast In First Outā or LIFO constraint.
The second paper presents another branch-and-cut algorithm for a vehicle routing and loading problem with two-dimensional rectangular items. The loading area of the vehicles is also a rectangular area where the items are taken out from one side. A constraint states that the items of a given customer must be directly accessible at delivery time.
The last paper considers a stochastic vehicle routing and loading problem with two- dimensional rectangular items where the dimensions of some items are unknown when the routes are planned. However, it is possible to associate a discrete probability distribution on the dimensions of these items. The problem is solved with the Integer L-Shaped method
A Lagrangian Approach for The Airfreight Consolidation Problem Under Pivot-weight
International airfreight forwarders are faced with the problem of consolidating ship- ments for efficient transportation by airline carriers. The use of standard unit loading devices (ULDs) is a solution adopted by the airfreight industry to speed up cargo loading, increase safety, and protect cargo. We study the airfreight consolidation problem from the forwarders perspective where a decision on the number of ULDs used and the assignment of shipments to ULDs is optimized. The cost of using a ULD consists of a fixed charge and depends on the weight of the cargo it contains. A ULD is charged at an under-pivot rate if the total weight is below a threshold limit, called the pivot-weight. Additional weight is charged at the over-pivot rate. We propose a solution methodology based on Lagrangian relaxation that is capable of providing high quality solutions in reasonable computational times. Besides, a high-quality lower bound, we propose three heuristics to generate feasible solutions, all based on the solution of the subproblems. The first, takes the solution of one of the subproblems and solves a restricted version of the original problem (LagHeur). The other two heuristics are a heuristic based on solving two knapsack problems (2knap) and a best-fit greedy heuristic (bestfit). Problems with up to 100 ULDs and 1000 shipments are solved to within an average of 1%, 2%, 2% of optimality in less than 51.05s, 50.57s and 589.16s by bestfit, 2knap and LagHeur, respectively
Algorithms for cutting and packing problems
Orientador: FlĆ”vio Keidi MiyazawaTese (doutorado) - Universidade Estadual de Campinas, Instituto de ComputaĆ§Ć£oResumo: Problemas de Corte e Empacotamento sĆ£o, em sua maioria, NP-difĆceis e nĆ£o existem algoritmos exatos de tempo polinomial para tais se for considerado P Āæ NP. AplicaƧƵes prĆ”ticas envolvendo estes problemas incluem a alocaĆ§Ć£o de recursos para computadores; o corte de chapas de ferro, de madeira, de vidro, de alumĆnio, peƧas em couro, etc.; a estocagem de objetos; e, o carregamento de objetos dentro de contĆŖineres ou caminhƵes-baĆŗ. Nesta tese investigamos problemas de Corte e Empacotamento NP-difĆceis, nas suas versƵes bi- e tridimensionais, considerando diversas restriƧƵes prĆ”ticas impostas a tais, a saber: que permitem a rotaĆ§Ć£o ortogonal dos itens; cujos cortes sejam feitos por uma guilhotina; cujos cortes sejam feitos por uma guilhotina respeitando um nĆŗmero mĆ”ximo de estĆ”gios de corte; cujos cortes sejam nĆ£o-guilhotinados; cujos itens tenham demanda (nĆ£o) unitĆ”ria; cujos recipientes tenham tamanhos diferentes; cujos itens sejam representados por polĆgonos convexos e nĆ£o-convexos (formas irregulares); cujo empacotamento respeite critĆ©rios de estabilidade para corpos rĆgidos; cujo empacotamento satisfaƧa uma dada ordem de descarregamento; e, cujos empacotamentos intermediĆ”rios e final tenham seu centro de gravidade dentro de uma regiĆ£o considerada "segura". Para estes problemas foram propostos algoritmos baseados em programaĆ§Ć£o dinĆ¢mica; modelos de programaĆ§Ć£o inteira; tĆ©cnicas do tipo branch-and-cut; heurĆsticas, incluindo as baseadas na tĆ©cnica de geraĆ§Ć£o de colunas; e, meta-heurĆsticas como o GRASP. Resultados teĆ³ricos tambĆ©m foram obtidos. Provamos uma questĆ£o em aberto levantada na literatura sobre cortes nĆ£o-guilhotinados restritos a um conjunto de pontos. Uma extensiva sĆ©rie de testes computacionais considerando instĆ¢ncias reais e vĆ”rias outras geradas de forma aleatĆ³ria foram realizados com os algoritmos desenvolvidos. Os resultados computacionais, sendo alguns deles comparados com a literatura, comprovam a validade dos algoritmos propostos e a sua aplicabilidade prĆ”tica para resolver os problemas investigadosAbstract: Several versions of Cutting and Packing problems are considered NP-hard and, if we consider that P Āæ NP, we do not have any exact polynomial algorithm for solve them. Practical applications arises for such problems and include: resources allocation for computers; cut of steel, wood, glass, aluminum, etc.; packing of objects; and, loading objects into containers and trucks. In this thesis we investigate Cutting and Packing problems that are NP-hard considering theirs two- and three-dimensional versions, and subject to several practical constraints, that are: that allows the items to be orthogonally rotated; whose cuts are guillotine type; whose cuts are guillotine type and performed in at most k stages; whose cuts are non-guillotine type; whose items have varying and unit demand; whose bins are of variable sizes; whose items are represented by convex and non-convex polygons (irregular shapes); whose packing must satisfy the conditions for static equilibrium of rigid bodies; whose packing must satisfy an order to unloading; and, whose intermediaries and resultant packing have theirs center of gravity inside a safety region; Such cutting and packing problems were solved by dynamic programming algorithms; integer linear programming models; branch-and-cut algorithms; several heuristics, including those ones based on column generation approaches, and metaheuristics like GRASP. Theoretical results were also provided, so a recent open question arised by literature about non-guillotine patterns restricted to a set of points was demonstrated. We performed an extensive series of computational experiments for algorithms developed considering several instances presented in literature and others generated at random. These results, some of them compared with the literature, validate the approaches proposed and suggest their applicability to deal with practical situations involving the problems here investigatedDoutoradoDoutor em CiĆŖncia da ComputaĆ§Ć£
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