Optimizing pre-processing and relocation moves in the Stochastic Container Relocation Problem

In container terminals, containers are often moved to other stacks in order to access containers that need to leave the terminal earlier. We propose a new optimization model in which the containers can be moved in two different phases: a pre-processing and a relocation phase. To solve this problem, we develop an optimal branch-and-bound algorithm. Furthermore, we develop a local search heuristic because the problem is NP-hard. Besides that, we give a rule-based method to estimate the number of relocation moves in a bay. The local search heuristic produces solutions that are close to the optimal solution. Finally, for instances in which the benefits of moving containers in the two different phases are in balance, the solution of the heuristic yields significant improvement compared to the existing methods in which containers are only moved in one of the two phases

Improving container terminal efficiency: New models and algorithms for Premarshalling and Stowage Problems

El desarrollo del contenedor ha revolucionado el comercio marítimo de mercancías, permitiendo la manipulación de carga de diversos tipos y dimensiones con un costo reducido y disminuyendo el costo de importación de muchos productos, En la actualidad, aproximadamente el 90\% de la carga no a granel en todo el mundo se transporta en buques portacontenedores, cuyas capacidades han llegado a sobrepasar los 20000 TEUs (\emph{Twenty-foot Equivalent Unit}, unidad de medida correspondiente a un contenedor normalizado de 20 pies). Las terminales de contenedores tienen que hacer frente al creciente volumen de carga transportada, al aumento del tamaño de las naves y a las alianzas de las navieras. En este contexto, deben competir por menos servicios de barcos cada vez más grandes. Para ello, deben aumentar su eficiencia, optimizando los recursos existentes. En esta tesis se estudian dos problemas de optimización combinatoria, el problema de premarshalling y el problema de la estiba, que surgen en el patio y en el muelle de las terminales de contenedores, antes y durante las operaciones de carga y descarga de los buques, y cuya resolución deriva en una disminución del tiempo de atraque y, por lo tanto, en un aumento de la eficiencia de las terminales. El problema de premarshalling prepara el patio de contenedores antes de la llegada del buque, usando las grúas de patio cuando la carga de trabajo es mínima, con el fin de evitar un mayor número de recolocaciones a la llegada del buque y así acelerar los tiempos de servicio. El objetivo clásico de este problema ha sido reducir al mínimo el número de movimientos necesarios para eliminar los contenedores que bloquean la retirada de otros dentro de una bahía. De este modo, el número de movimientos se ha tomado como un indicador del tiempo de grúa. No obstante, en esta tesis se prueba que considerando como objetivo el tiempo real que la grúa emplea en realizar los movimientos, se puede reducir hasta un 24\% el tiempo total empleado. Para la resolución de ambos problemas, el premarshalling con función objetivo clásica y el premarshalling con la nueva función objetivo, se han desarrollado diversos modelos matemáticos y algoritmos Branch and Bound con nuevas cotas superiores e inferiores, reglas de dominancia y algoritmos heurísticos integrados en el proceso de ramificación. Por lo que respecta al problema de la estiba, se ha estudiado el problema multi-puerto que busca obtener un plan de estiba del barco de modo que se reduzca al mínimo el número total de movimientos improductivos en las operaciones de carga y descarga a lo largo de la ruta en la que presta servicio. Comenzamos estudiando el problema simplificado, en el que no se consideran restricciones de tamaño ni de peso de los contenedores, y progresivamente se van introducido restricciones más realistas, desarrollando modelos matemáticos, heurísticas, metaheurísticas y mateheurísticas. Estos procedimientos son capaces de resolver instancias de gran tamaño correspondientes a los barcos de mayor capacidad que se encuentran actualmente en el sector.The development of containers has revolutionized maritime trade by making it possible to handle various types and sizes of cargo at a reduced cost, lowering the import cost of many products to such an extent that it is sometimes cheaper to transport goods to the other side of the world than to produce them locally. Nowadays, about 90 per cent of non-bulk cargo worldwide is carried on container ships with capacities exceeding 20,000 TEUs (Twenty-foot Equivalent Units). Container terminals have to cope with the increase in the volumes of cargo transported, the ever-larger ships, and the consolidation of shipping companies. In this context, they have to compete for fewer calls of larger ships. Since they cannot simply increase the number of cranes indefinitely, they have to improve efficiency by optimizing the available resources. This thesis studies two combinatorial optimization problems, the premarshalling problem and the stowage problem. These problems arise in the yard and the seaside of container terminals, before and during the loading and unloading operations of the ships, and make it possible to reduce the berthing time and thus to increase container terminal efficiency. The premarshalling problem prepares the container yard before the arrival of the ship, using the yard cranes when the workload at the terminal is at a minimum to rearrange the yard in order to avoid container relocations when the vessel arrives and to speed up the service times. The classic objective of this problem is to minimize the number of movements required to remove containers blocking the retrieval of others within a bay. Thus, the number of movements has been used as an indicator of crane time. However, this thesis shows that considering the real time that the crane takes to perform the movements as the target, the total time spent by the crane can be cut down up to 24 per cent. To solve both problems, premarshalling with the classic objective function and premarshalling with the new objective function, this thesis develops several mathematical models and branch and bound algorithms with new upper and lower bounds, dominance rules and heuristic algorithms integrated in the branching process. With regard to the stowage problem, the multi-port problem is addressed, seeking to obtain a stowage plan for the ship so as to minimize the total number of unproductive moves in the loading/unloading operations along the trade route of the ship. We start with a simplified problem, in which no size and weight constraints are considered, and progressively introduce more realistic constraints, developing mathematical models, metaheuristics, and matheuristics. These procedures are able to solve very large instances, corresponding to the largest ships in service

Flexible ship loading problem with transfer vehicle assignment and scheduling

This paper presents the flexible containership loading problem for seaport container terminals. The integrated management of loading operations, planning of the transport vehicles to use and their scheduling is what we define as the Flexible Ship Loading Problem (FSLP). The flexibility comes from a cooperative agreement between the terminal operator and the liner shipping company, specifying that the terminal has the right to decide which specific container to load for each slot obeying the class-based stowage plan received from the liner. We formulate a mathematical model for the problem. Then we present various modelling enhancements and a mathematical model to obtain strong lower bounds. We also propose a heuristic algorithm to solve the problem. It is shown that enhancements improve the performance of formulation significantly, and the heuristic efficiently generates high-quality solutions. Results also point out that substantial cost savings can be achieved by integrating the ship loading operations

Network hub locations problems: the state of the art

Cataloged from PDF version of article.Hubs are special facilities that serve as switching, transshipment and sorting points in many-to-many distribution systems. The hub location problem is concerned with locating hub facilities and allocating demand nodes to hubs in order to route the traffic between origin-destination pairs. In this paper we classify and survey network hub location models. We also include some recent trends on hub location and provide a synthesis of the literature. (C) 2007 Elsevier B.V. All rights reserved

A Polyhedral Study of Mixed 0-1 Set

We consider a variant of the well-known single node fixed charge network flow set with constant capacities. This set arises from the relaxation of more general mixed integer sets such as lot-sizing problems with multiple suppliers. We provide a complete polyhedral characterization of the convex hull of the given set