Sotirios Theofanis

Initialization of the Benders master problem using valid inequalities applied to fixed-charge network problems

Highlights? We study the application of Benders decomposition to the fixed-charge network problem. ? A method for the initialization of Benders master problem is presented. ? Master problem is initialized by a series of generally applicable valid inequalities. ? Initializing the master problem, the algorithm starts from narrower bounds. ? This method significant decreases the number of iterations and the CPU solution time. Network problems concern the selection of arcs in a graph in order to satisfy, at minimum cost, some flow requirements, usually expressed in the form of node-node pair demands. Benders decomposition methods, based on the idea of partitioning of the initial problem to two sub-problems and on the generation of cuts, have been successfully applied to many of these problems. This paper presents a novel way to reinitialize the Benders master problem for this group of problems using a series of valid inequalities. A generic presentation of the developed valid inequalities is presented as well as a case study of a refinery system is used in order to illustrate the advantage of the proposed procedure. The valid inequalities significantly restrict the solution space of the Benders master problem from the first iteration of the algorithm leading to improved convergence.

An optimization based genetic algorithm heuristic for the berth allocation problem

Genetic algorithms have been used extensively in the studies on the Berth allocation problem (BAP). In this paper we present an optimization based genetic algorithm heuristic for the discrete and dynamic BAP that is independent of the objective function of the problem. It is evaluated by considering the problem of allocating space at a berth for vessels with the objective of minimizing the total weighted service time of all the vessels. The problem is formulated as a linear mixed integer program. Computational experiments are reported to evaluate the efficiency of the proposed heuristic.

A Multi-Objective Decision and Analysis Approach for the Berth Scheduling Problem

Berth scheduling can be described as the resource allocation problem of berth space to vessels in a container terminal. When defining the allocation of berths to vessels container terminal operators set several objectives which ideally need to be optimized simultaneously. These multiple objectives are often non-commensurable and gaining an improvement on one objective often causes degrading performance on the other objectives. In this paper, the authors present the application of a multi-objective decision and analysis approach to the berth scheduling problem, a resource allocation problem at container terminals. The proposed approach allows the port operator to efficiently select a subset of solutions over the entire solution space of berth schedules when multiple and conflicting objectives are involved. Results from extensive computational examples using real-world data show that the proposed approach is able to construct and select efficient berth schedules, is consistent, and can be used with confidence.

Scheduling of Inbound Trucks at a Cross-Docking Facility: Bi-Objective VS Bi-Level Modeling Approaches

This paper examines the problem of scheduling of inbound trucks to the inbound doors at a cross-docking facility. The authors optimize for two conflicting objectives: minimize the total service time for all the inbound trucks and minimize the delayed completion of service for a subset of the inbound trucks, which are considered as preferential customers. The problem is formulated as a bi-objective and as a bi-level mixed integer problem. Due to the nature of the former and the complexity of the latter formulation, a genetic algorithm and a k-th best based algorithm are proposed as the solution approaches. Computational examples are used to discuss the advantages and drawbacks of each formulation.

Scheduling of Inbound and Outbound Trucks at Cross-Docks: Modeling and Analysis

A model is developed for both time and space scheduling of inbound and outbound trucks at a cross-dock facility under various objectives. Three different objectives in optimizing cross-dock operations are presented, and the justification for the use of these objectives is given. A linear mixed integer formulation of the problem is presented, and a restriction–approximation approach is developed and applied to determine the truck scheduling at a sample cross-dock facility. This paper also analyzes the behavior of each of the objectives and provides a comprehensive analysis of the results. Pareto and post-Pareto analyses of the multiobjective problem are presented.

A freight network planning model in oligopolistic shipping markets

The paper presents a multi-level hierarchical approach which models the oligopolistic behavior of carriers in maritime freight transportation networks. With the merger of the carriers’ industry and some dominant carriers in today’s shipping markets, carrier competition frequently exhibits an oligopolistic nature. This study considers the following three types of carriers; ocean carriers, land carriers, and port terminal operators. The oligopolistic ocean carriers, land carriers, and port terminal operators compete with each other in their pricing and routing decisions. The carriers determine service charges and delivery routes at different parts of the multi-modal freight network, creating hierarchical relationships. When using a game theoretic approach, ocean carriers become the leaders in an oligopoly shipping market. When dealing with individual carrier problems, the Nash equilibrium reveals the optimal decision where each carrier obtains the greatest profit. A three-level model is formulated to capture the interactions among different types of carriers. The validity and capability of the model gets demonstrated through an empirical example.

Modeling Carrier Interactions in an International Freight Transport System

This paper presents a novel multi-level hierarchical approach which models carrier interactions in international maritime freight transportation networks. Ocean carriers, land carriers and port terminal operators are considered. Port terminal operators, providing transportation services within a port complex, are regarded as a special type of the carrier, based on their behavior. The carriers make pricing and routing decisions at different parts of the multimodal network, having hierarchical relationships. Ocean carriers are regarded as the leaders in a maritime shipping market. Port terminal operators are the followers of ocean carriers as well as the leaders of land carriers. The individual carrier problem is formulated at each level using Nash equilibrium to find the optimal service charge and routing pattern for which each carrier obtains the greatest profit. Interactions among different types of carriers are captured in a three-level model. The concept of multi-leader-follower game is applied to a multi-level game. A numerical example is used to demonstrate the validity of the developed three-level model.

Oil spills in maritime transport : Call for action

Maritime transport plays a vital role in the economic growth and global competitiveness of the regions that it serves. It offers an enormous potential for sustainable and environmentally friendly transport. The international maritime community, however, is faced with a major challenge: to protect the marine environment from pollution related to oil spills. A parallelism between resolutions adopted by national and international bodies and the oil spill incidents that triggered them is presented. The focus is on reviewing records of maritime casualties associated with massive environmental pollution. It is an attempt to shed light on how these incidents affect the formulation and implementation of the global marine environment protection policy as well as the role of the International Maritime Organization in dealing with these problems.

Developing a Port Energy Management Plan: Issues, Challenges, and Prospects

Raising the environmental profile of European ports and promoting excellence in port environmental management and performance are key priorities for European ports policy. The need for well-connected port infrastructure, efficient and reliable port services, and transparent port funding is significant. Reducing energy consumption in ports has become a major concern for all port community stakeholders and ranks third in the top 10 environmental priorities of the European port sector for 2013. This concern has led 57% of European ports to develop energy efficiency programs and 20% of them to adopt measures for directly producing energy from renewable sources. This paper presents a structured approach for developing a port energy management plan (EMP) that highlights the main issues, challenges, and prospects that should be taken into account. The role of European ports in changing energy policy is discussed, and the value of a port EMP, either at the port authority level or at the terminal operator level, is highlighted. Pertinent issues for developing such a plan are described and analyzed. Insight gained from the implementation of the approach in six Mediterranean ports, within the context of the Greenberth project, is reported, and targeted recommendations and conclusions are provided about how this diverse experience can contribute to a robust port EMP.

Incorporating Maritime Stakeholder Perspectives for Implementing an ‘Inland-Depots-for-Empty-Containers’ System Using an Analytic Hierarchy Process

Container movement involves several stakeholders where each group is focused on achieving its own objectives. By actively considering the perspective of different maritime stakeholders, this paper identifies a set of implementation strategies and prioritizes them to successfully implement an ‘Inland-Depots-for-Empty-Containers’ (IDEC) system in a region. It builds on the authors’ earlier work that developed and evaluated an IDEC system to minimize the overall system costs associated with regional repositioning of empty containers. Based on the benefits, costs and risks perceived by the involved maritime stakeholders on IDEC implementation, the authors identify strategies that may facilitate the building process and establish the system sustainably. They judge and prioritize the strategies in an Analytic Hierarchy Process (AHP) framework and present results based on their analysis. The authors believe that this research will benefit authorities considering an IDEC implementation strategy and also AHP practitioners.