A Simulation-Based Optimization Approach for Integrated Port Resource Allocation Problem

Todays, due to the rapid increase in shipping volumes, the container terminals are faced with the challenge to cope with these increasing demands. To handle this challenge, it is crucial to use flexible and efficient optimization approach in order to decrease operating cost. In this paper, a simulation-based optimization approach is proposed to construct a near-optimal berth allocation plan integrated with a plan for tug assignment and for resolution of the quay crane re-allocation problem. The research challenges involve dealing with the uncertainty in arrival times of vessels as well as tidal variations. The effectiveness of the proposed evolutionary algorithm is tested on RAJAEE Port as a real case. According to the simulation result, it can be concluded that the objective function value is affected significantly by the arrival disruptions. The result also demonstrates the effectiveness of the proposed simulation-based optimization approach. </span

Sequence-Based Simulation-Optimization Framework With Application to Port Operations at Multimodal Container Terminals

It is evident in previous works that operations research and mathematical algorithms can provide optimal or near-optimal solutions, whereas simulation models can aid in predicting and studying the behavior of systems over time and monitor performance under stochastic and uncertain circumstances. Given the intensive computational effort that simulation optimization methods impose, especially for large and complex systems like container terminals, a favorable approach is to reduce the search space to decrease the amount of computation. A maritime port can consist of multiple terminals with specific functionalities and specialized equipment. A container terminal is one of several facilities in a port that involves numerous resources and entities. It is also where containers are stored and transported, making the container terminal a complex system. Problems such as berth allocation, quay and yard crane scheduling and assignment, storage yard layout configuration, container re-handling, customs and security, and risk analysis become particularly challenging. Discrete-event simulation (DES) models are typically developed for complex and stochastic systems such as container terminals to study their behavior under different scenarios and circumstances. Simulation-optimization methods have emerged as an approach to find optimal values for input variables that maximize certain output metric(s) of the simulation. Various traditional and nontraditional approaches of simulation-optimization continue to be used to aid in decision making. In this dissertation, a novel framework for simulation-optimization is developed, implemented, and validated to study the influence of using a sequence (ordering) of decision variables (resource levels) for simulation-based optimization in resource allocation problems. This approach aims to reduce the computational effort of optimizing large simulations by breaking the simulation-optimization problem into stages. Since container terminals are complex stochastic systems consisting of different areas with detailed and critical functions that may affect the output, a platform that accurately simulates such a system can be of significant analytical benefit. To implement and validate the developed framework, a large-scale complex container terminal discrete-event simulation model was developed and validated based on a real system and then used as a testing platform for various hypothesized algorithms studied in this work

Simulation Modeling for Ship Traffic Flow in Entrance Channel

The design of coastal entrance channel is a complex challenge, considering the stochastic environment and time-consuming calculation works. Therefore, we implement a process-interaction-based simulation model for ship operation (PI-SMSO) using Java language to help the designers to determine the dimensions of entrance channels. The PI-SMSO component simulates ships in and out through a one- or two-way traffic channel, or a one-way channel with a ship-passing anchorage, and ships discharging/loading at berths. Finally, we apply the PI-SMSO to a Chinese coal-import terminal, to explore its possible bottlenecks by evaluating the performance of entrance channel system, and determine the available improvement strategies according to the simulated port performance. The case study proves that the proposed PI-SMSO effectively simulates the ship traffic flow in entrance channel and provides a decision support for evaluating entrance channel system

Integrated Scheduling of Vessels, Cranes and Trains to Minimize Delays in a Seaport Container Terminal

The multiple processes taking place on a daily basis at an intermodal container terminal are often considered individually, given the complexity of their joint consideration. Nevertheless, the integrated planning and scheduling of operations in an intermodal terminal, including the arrivals and departures of trains and vessels, is a very relevant topic for terminal managers, which can benefit from the application of Operations Research (OR) techniques to obtain near-optimal solutions without excessive computational cost. Applying the functional integration technique, we present here a mathematical model for this terminal planning process, and solve it using heuristic procedures, given its complexity and size. Details on the benchmark comparison of a genetic algorithm, a simulated annealing routine and a tabu search are provided for different problem instances

Berth scheduling problem considering traffic limitations in the navigation channel

In view of the trend of upsizing ships, the physical limitations of natural waterways,huge expenses, and unsustainable environmental impact of channel widening, this paper aims toprovide a cost-efficient but applicable solution to improve the operational performance of containerterminals that are enduring inefficiency caused by channel traffic limitations. We propose a novelberth scheduling problem considering the traffic limitations in the navigation channel, which appearsin many cases including insufficient channel width, bad weather, poor visibility, channel accidents,maintenance dredging of the navigation channel, large vessels passing through the channel, andso on. To optimally utilize the berth and improve the service quality for customers, we proposea mixed-integer linear programming model to formulate the berth scheduling problem under theone-way ship traffic rule in the navigation channel. Furthermore, we develop a more generalizedmodel which can cope with hybrid traffic in the navigation channel including one-way traffic,two-way traffic, and temporary closure of the navigation channel. For large-scale problems, a hybridsimulated annealing algorithm, which employs a problem-specific heuristic, is presented to reducethe computational time. Computational experiments are performed to evaluate the effectiveness andpracticability of the proposed method

Does Aid Induce Brain Drain? The Effect of Foreign Aid on Migration Selection

Recent evidence suggests that aid induces migration. However, total migration is quite general from a policy perspective since what explains the welfare consequences of migration is the extent of emigration selection. In this paper we ask whether skilled or unskilled migration is more sensitive to aid and to the different mechanisms through which aid may affect self-selection among international emigrants. We show that aid induces positive selection. And that the effect on skilled migration is larger than the effect on unskilled migration. As possible mechanisms to explain the relation, we find that aid induces skilled migration by reducing transaction and information costs, by improving the distribution of schooling, and by helping to overcome liquidity constraints.Foreign aid, International migration, Self-selection, Brain drain.

BER-Adaptive RMLSA Algorithm for Wide-Area Flexible Optical Networks

Wide-area optical networks face significant transmission challenges due to the relentless growth of bandwidth demands experienced nowadays. Network operators must consider the relationship between modulation format and maximum reach for each connection request due to the accumulation of physical layer impairments in optical fiber links, to guarantee a minimum quality of service (QoS) and quality of transmission (QoT) to all connection requests. In this work, we present a BER-adaptive solution to solve the routing, modulation format, and spectrum assignment (RMLSA) problem for wide-area elastic optical networks. Our main goal is to maximize successful connection requests in wide-area networks while choosing modulation formats with the highest efficiency possible. Consequently, our technique uses an adaptive bit-error-rate (BER) threshold to achieve communication with the best QoT in the most efficient manner, using the strictest BER value and the modulation format with the smallest bandwidth possible. Additionally, the proposed algorithm relies on 3R regeneration devices to enable long-distances communications if transparent communication cannot be achieved. We assessed our method through simulations for various network conditions, such as the number of regenerators per node, traffic load per user, and BER threshold values. In a scenario without regenerators, the BER-Adaptive algorithm performs similarly to the most relaxed fixed BER threshold studied in blocking probability. However, it ensures a higher QoT to most of the connection requests. The proposed algorithm thrives with the use of regenerators, showing the best performance among the studied solutions, enabling long-distance communications with a high QoT and low blocking probability