Heuristic for the preemptive asymmetric stacker crane problem

International audienceIn this paper, we deal with the preemptive asymmetric stacker crane problem in an heuristic way. We first present some theoretical results which allow us to turn this problem into a specific tree design problem. We next derive from this new representation a simple, efficient local search heuristic, as well as an original LIP model. We conclude by presenting experimental results which aim at both testing the efficiency of our heuristic and at evaluating the impact of the preemption hypothesis

A Branch-and-Cut Algorithm for the Pickup and Delivery Traveling Salesman Problem with LIFO Loading

In the Traveling Salesman Problem with Pickup and Delivery (TSPPD) a single vehiclemust serve a set of customer requests, each defined by an origin location where a load must be picked up, and a destination location where the load must be delivered. The problem consists of determining a shortest Hamiltonian cycle through all locations while ensuring that the pickup of each request is performed before the corresponding delivery. This article addresses a variant of the TSPPD in which pickups anddeliveries must be performed according to a Last-In First-Out (LIFO) policy. We propose three mathematical formulations for this problem and several families of valid inequalities which are used within a branch-and-cut algorithm. Computational results performed on test instances from the literature show that most instances with up to 17 requests can be solved in less than 10 min, whereas the largest instance solved contains 25 requests

Optimização de processos na cadeia de abastecimento : o caso do transporte de mercadorias

Dissertação de mestrado em Engenharia de SistemasNum passado recente, tem-se verificado uma melhoria contínua das condições de transporte. As infraestruturas construídas, desde estradas a linhas ferroviárias tiveram como objectivo melhorar a qualidade de vida da população, diminuir o tempo e custos associados ao transporte e distribuição, quer de pessoas quer de mercadorias. Para que esta qualidade exista é necessário criar condições para tal, e assim é essencial optimizar as rotas dos veículos e a disposição das cargas transportadas. É nesta área que o presente trabalho se enquadra e de forma a contextualizar o problema e perceber o trabalho realizado na área até ao momento, é apresentado um resumo dos vários estudos desenvolvidos na área num capítulo de revisão de literatura. A realização desta dissertação foi constituída por duas fases distintas. Uma primeira fase de pesquisa de aplicações internacionais e nacionais que permitem optimizar rotas, na qual para as aplicações internacionais só foram analisadas aquelas que consideram restrições dos produtos transportados como o peso, altura, comprimento, largura e volume. Na análise das aplicações são descritas as suas funcionalidades e os principais clientes. Adicionalmente, e caso as aplicações tenham um módulo que trata do carregamento dos veículos, é feita a sua descrição. No fim dessa fase, é apresentada uma análise crítica das aplicações e uma tabela de síntese onde são apresentadas as suas principais características. O objectivo da segunda fase foi desenvolver e testar várias abordagens heurísticas para o problema de encaminhamento de veículos com restrições de carga a duas dimensões (2L-CVRP). Os testes de desempenho dessas heurísticas foram realizados sobre as mesmas instâncias usadas no trabalho desenvolvido por Iori (Iori, Salazar-Gonzalez, & Vigo, 2007) na qual garante resultados óptimos recorrendo a um algoritmo exacto. O problema em estudo é caracterizado por um depósito central onde estão colocados diversos veículos que têm a função de transportar encomendas efectuadas por clientes. O objectivo é minimizar tanto a distância total percorrida pelos veículos assim como o número de veículos utilizados. No final, temos uma série de veículos, em que cada um tem uma rota ordenada de clientes. Comparando os resultados das heurísticas com o algoritmo exacto, é natural que os resultados das heurísticas sejam piores no que diz respeito ao número de veículos utilizados e às distâncias percorridas. Contudo, a motivação esteve em tentar aproximar-se da qualidade dos resultados do algoritmo exacto em tempos computacionais bem menores. Nos três algoritmos desenvolvidos foram identificadas três zonas críticas, as estratégias de selecção dos clientes, a estratégia de colocação de itens nos veículos e a estratégia para controlar a distância percorrida – raio de movimentação dos veículos.In the recent past, there has been a continuous improvement of transport conditions. The infrastructures built, from roads to railways lines, were aimed to improve the population life quality, decrease the time and costs associated to the transport and distribution of people and goods. For this quality to exist, it is necessary to create conditions for that, and so it is essential to optimise the vehicle routing and the arrangement of the cargoes. This is the context of the current work and in order to understand what was done, a summary of several studies is presented in a state of art chapter. The development of this dissertation was composed by two distinct phases. An initial research phase of international and national software that allows routing optimization was made and, in the case of international software, we only analysed those who consider cargoes restrictions like, weight, height, length, width and volume. In the software analysis are described their main features and major customers and, if they have a module that deals with the vehicle loading, its description is made. At the end of this phase, a critical analysis and a summary table with the software main features are presented. The aim of the second stage was to develop and test heuristic approaches to the vehicle routing problem with two-dimensional loading constraints (2L-CVRP). Performance tests on this heuristics were performed on the same instances presented in Iori´s work (Iori, Salazar-Gonzalez, & Vigo, 2007), in which an exact algorithm was used to ensure optimal results. The problem features a central depot, where various vehicles are placed and each has the function of transporting orders placed by customers. The main objective is to minimize the total travelled distance and the number of vehicles used. In the end, we have a set of vehicles, in which, each has an ordered rout of clients. Following this approach and to provide a basis for comparison, three constructive heuristics were developed in order to have access to a range of different outcomes and so, in addition of being compared with the exact algorithm, the developed algorithms can be compared between them. The items that are used for analysis are, the number of vehicles used in an instance, the total distance travelled and the runtime. When compared with the exact algorithm, it is natural that the heuristics present worse results in terms of number of vehicles used and total distance travelled. However, the motivation was to try to approach the quality of the results presented by the exact algorithm, in less time. In the three algorithms developed, we identified three critical areas, the customers selection strategy, the placement of items in vehicles strategy and the control of distance strategy - radius of movement by vehicles between clients

The traveling salesman problem with three-dimensional loading constraints

Orientador: Flávio Keidi MiyazawaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: Nesta dissertação de mestrado apresentamos um método exato para o Problema do Caixeiro Viajante com Restrições de Empacotamento Tridimensional, que combina o Problema do Caixeiro Viajante o Problema de Empacotamento Tridimensional com Restrição de Ordem. Neste problema, um veículo deve partir carregado de um depósito e entregar caixas em pontos pré-definidos para seus clientes. Cada cliente tem um conjunto de caixas que deve receber e o objetivo é minimizar o custo de deslocamento do veículo. As caixas devem ser retiradas a partir da porta do contêiner do veículo e a remoção das caixas de um cliente não podem ser obstruídas pelas caixas a serem descarregadas posteriormente. Propomos uma abordagem exata baseada em branch-and-cut para buscar uma rota de custo mínimo. Apresentamos algumas adaptações de algoritmos da literatura e uma formulação em Programação por Restrições para encontrar um empacotamento que obedece restrições de ordem. Realizamos testes computacionais em instâncias geradas aleatoriamente e comparamos resultados com os algoritmos adaptados da literatura. Os resultados foram bastante satisfatórios resolvendo instâncias de tamanho médio em tempo computacional aceitável na práticaAbstract: We present an exact method for the Traveling Salesman Problem with Three-dimensional Loading Constraints. This problem combines the Traveling Salesman Problem, and the Three- Dimensional Packing Problem With Loading Constraints. In this problem, a vehicle must be loaded at the depot and deliver boxes to the customers. Every customer has a set of boxes that should receive and our goal is to minimize the travel cost of the vehicle. Unloading is done through a single side of the container and items from an unloading customer must not be blocked by items to be delivered later. We propose exact and heuristic branch-and-cut algorithm to find a minimum cost route. Adaptations of algorithms from the literature and a Constraint Programming formulation is presented to find a packing that consider unloading contraints. We performed computational tests on instances randomly generated and compared results with the algorithms adapted from literature. The results were quite satisfactory resolving several instances in reasonable computational timeMestradoCiência da ComputaçãoMestre em Ciência da Computaçã

Essays on Shipment Consolidation Scheduling and Decision Making in the Context of Flexible Demand

This dissertation contains three essays related to shipment consolidation scheduling and decision making in the presence of flexible demand. The first essay is presented in Section 1. This essay introduces a new mathematical model for shipment consolidation scheduling for a two-echelon supply chain. The problem addresses shipment coordination and consolidation decisions that are made by a manufacturer who provides inventory replenishments to multiple downstream distribution centers. Unlike previous studies, the consolidation activities in this problem are not restricted to specific policies such as aggregation of shipments at regular times or consolidating when a predetermined quantity has accumulated. Rather, we consider the construction of a detailed shipment consolidation schedule over a planning horizon. We develop a mixed-integer quadratic optimization model to identify the shipment consolidation schedule that minimizes total cost. A genetic algorithm is developed to handle large problem instances. The other two essays explore the concept of flexible demand. In Section 2, we introduce a new variant of the vehicle routing problem (VRP): the vehicle routing problem with flexible repeat visits (VRP-FRV). This problem considers a set of customers at certain locations with certain maximum inter-visit time requirements. However, they are flexible in their visit times. The VRP-FRV has several real-world applications. One scenario is that of caretakers who provide service to elderly people at home. Each caretaker is assigned a number of elderly people to visit one or more times per day. Elderly people differ in their requirements and the minimum frequency at which they need to be visited every day. The VRP-FRV can also be imagined as a police patrol routing problem where the customers are various locations in the city that require frequent observations. Such locations could include known high-crime areas, high-profile residences, and/or safe houses. We develop a math model to minimize the total number of vehicles needed to cover the customer demands and determine the optimal customer visit schedules and vehicle routes. A heuristic method is developed to handle large problem instances. In the third study, presented in Section 3, we consider a single-item cyclic coordinated order fulfillment problem with batch supplies and flexible demands. The system in this study consists of multiple suppliers who each deliver a single item to a central node from which multiple demanders are then replenished. Importantly, demand is flexible and is a control action that the decision maker applies to optimize the system. The objective is to minimize total system cost subject to several operational constraints. The decisions include the timing and sizes of batches delivered by the suppliers to the central node and the timing and amounts by which demanders are replenished. We develop an integer programing model, provide several theoretical insights related to the model, and solve the math model for different problem sizes

Conception d’un réseau de transport en commun pour le transport des patients sur l’Île-de-Montréal

RÉSUMÉ : La loi 10 a souhaité une nouvelle organisation du système de soins de santé québécois. Elle a engendré en avril 2015 la création de Centres Intégrés (Universitaires) de Santé et de Services Sociaux (CI(U)SSS). Dans ce contexte de centralisation des établissements de santé québécois, nous avons conduit une étude de terrain de l’organisation du transport non urgent des patients entre les établissements de quatre CIUSSSs sur l’Ile-de-Montréal. Cette étude a révélé que ce type de transport, qui représente un enjeu financier et organisationnel important pour les CIUSSSs, peut être optimisé. En effet, ces établissements de santé ont longtemps fonctionné individuellement. Malgré la centralisation administrative effective, la prise de décision concernant l’organisation du transport externe non urgent des patients est encore visualisée à l’échelle de chaque établissement, voire au niveau de chaque unité. Les processus suivis peuvent ainsi varier d’une unité à l’autre d’un même établissement, même si la plupart des problématiques et moyens de transport utilisés sont partagés. Les déplacements actuellement réalisés par les patients de ces CIUSSSs peuvent présenter une certaine régularité, parce qu’ils concernent des traitements réguliers ou des activités mis en place dans l’objectif d’aider les personnes à vivre chez elles autonomes le plus longtemps possible. De plus, l’existence de corridors de service entre certains établissements peut augmenter la fréquence de certains trajets. Homogénéiser l’organisation actuelle du transport externe non urgent des patients pour la centraliser pourrait donc permettre de réduire la part importante du budget qui lui est accordée et d’augmenter la qualité du service proposé aux patients. Suite à ces observations et connaissant les perspectives d’évolution de la population traitée par le système de soins de santé, nous nous sommes demandé si organiser le transport non urgent des patients de ces CIUSSSs à l’aide d’un réseau de transport en commun serait possible et rentable. Un tel réseau devrait être adapté à la condition physique des patients. Majoritairement à mobilité réduite, ils se déplacent en fauteuils roulants et ne peuvent ni circuler pour rejoindre un arrêt du réseau ni subir un transfert de ligne sur leur trajet. La configuration actuelle des véhicules est telle que les routes dessinées devront aussi permettre de servir la demande en respectant la contrainte de Last-In-First-Out (LIFO), que nous introduisons en conception de réseau. La demande actuelle étant très peu dense, nous avons défini un réseau de transport adapté construit zone par zone. Dans chaque zone géographique construite à l’aide d’un double partitionnement des demandes de transport basé sur la densité, nous avons construit des réseaux à deux niveaux. Nous avons d’abord tracé des routes permettant de servir la partie la plus régulière de la demande. Nous avons ensuite autorisé une certaine déviation des routes dessinées pour affecter les patients aux routes du réseau. Au cours des observations terrain qui ont permis de statuer les hypothèses du problème, nous avons constitué et analysé une base de données qui représente les demandes de transports apparues sur une période de vingt-cinq semaines entre avril et septembre 2016. Les tests réalisés à partir de ces demandes ont permis d’apprécier l’influence des paramètres choisis pour le partitionnement de la demande sur les réseaux obtenus et leur réponse quotidienne à la demande. Les résultats montrent que, dans l’organisation actuelle de la demande, l’association de la contrainte de LIFO et de l’interdiction du transfert de ligne est trop forte pour construire un réseau de transport en commun réaliste et financièrement rentable. Les réseaux construits offrent néanmoins une bonne qualité de transport aux patients. Les routes dessinées par la méthode que nous avons choisie permettent aussi de conclure que considérer l’organisation du transport externe non urgent des patients à l’échelle de l’Ile-de-Montréal sous la forme d’un transport à la demande est prometteuse.----------ABSTRACT : In 2015, the 10th law caused a overhaul of the health care system of Quebec. As an example, the health care facilities were consolidated into regional centers called Centres Intégrés (Universitaires) de Santé et de Services Sociaux (CI(U)SSS). In this context, we have led a field study regarding the organization of the external non-emergency patient transport services between the facilities of four CIUSSSs in Montreal. This survey raised that the organization of external non-emergency patient transport services, which is a major issue at both Financial and organizational points of view, can be improved. As a matter of fact, the facilities have been operating on their own for long. Then, despite the consolidation of administrative service is effective, the decision-making concerning the transportation of patients is still processed at the level of each facility, or even separately in the the care units of one place. Those process can then vary from one place to another, even though the means of transport used and the problems faced are common. The demands of transport from the patients of these CIUSSSs can currently occur on a regular basis, since they are raised by regular treatments or activities aimed at making them be able to live at home independently as long as they can. Furthermore, service corridors exist between several health care centers that can increase some trips frequency. In view of this, standardizing the existing organization of the external non-emergency transportation of patients could help reducing the major part of the budget currently dedicated to this field, and to improve the quality of the service offered to the patients. Considering this and the expected evolution of the patient population, we wondered if a transit network could profitably and suitably be designed to answer the demand of transportation in these CIUSSSs. Such a network should be adapted to the physical and psychological conditions of the patients. Most of them are persons with reduced mobility, then move in wheelchairs and can neither join a stop of the network nor accept any transfer between lines during their travel. Presently, the configuration of the vehicles enforce a Last-In-First-Out (LIFO) constraint, which we introduce in network design. Presently, the demand of transport is really sparse. We then decided to build our network per zone. In each geographical zone defined by a two-level density clustering of the demands, we designed two-level networks. First, we drew routes aimed at answering the most regular demands. Second, we allowed a certain deviation of these routes for the network to serve more demands. Throughout the field study aimed at defining the problem, we gathered a data basis which reflects the transportation demands that occurred over a period of twenty-five weeks between April and September 2016. The experiments allowed us to assess how the parameters chosen influence the network designed and their ability to respond to the daily demand for transports. The results show that under the current organization of the demands of transport, adding the LIFO constraint and avoiding every transfer between lines makes difficult, if not impossible, the design of a realistic and profitable network. Nevertheless, the networks designed offer a very good quality service to the patients. From the routes drawn by the method we have chosen, we can also conclude that considering the organization of the external non-emergency transportation of patients at the level of a whole region as a demand-responsive transport problem could show promise

Constrained Task Assignment and Scheduling on Networks of Arbitrary Topology.

This dissertation develops a framework to address centralized and distributed constrained task assignment and task scheduling problems. This framework is used to prove properties of these problems that can be exploited, develop effective solution algorithms, and to prove important properties such as correctness, completeness and optimality. The centralized task assignment and task scheduling problem treated here is expressed as a vehicle routing problem with the goal of optimizing mission time subject to mission constraints on task precedence and agent capability. The algorithm developed to solve this problem is able to coordinate vehicle (agent) timing for task completion. This class of problems is NP-hard and analytical guarantees on solution quality are often unavailable. This dissertation develops a technique for determining solution quality that can be used on a large class of problems and does not rely on traditional analytical guarantees. For distributed problems several agents must communicate to collectively solve a distributed task assignment and task scheduling problem. The distributed task assignment and task scheduling algorithms developed here allow for the optimization of constrained military missions in situations where the communication network may be incomplete and only locally known. Two problems are developed. The distributed task assignment problem incorporates communication constraints that must be satisfied; this is the Communication-Constrained Distributed Assignment Problem. A novel distributed assignment algorithm, the Stochastic Bidding Algorithm, solves this problem. The algorithm is correct, probabilistically complete, and has linear average-case time complexity. The distributed task scheduling problem addressed here is to minimize mission time subject to arbitrary predicate mission constraints; this is the Minimum-time Arbitrarily-constrained Distributed Scheduling Problem. The Optimal Distributed Non-sequential Backtracking Algorithm solves this problem. The algorithm is correct, complete, outputs time optimal schedules, and has low average-case time complexity. Separation of the task assignment and task scheduling problems is exploited here to ameliorate the effects of an incomplete communication network. The mission-modeling conditions that allow this and the benefits gained are discussed in detail. It is shown that the distributed task assignment and task scheduling algorithms developed here can operate concurrently and maintain their correctness, completeness, and optimality properties.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91527/1/jpjack_1.pd