publications

2021

1. Thesis

   Management of AGV Fleet in Automated Container Terminal

   Stephen, Aloisius

   National University of Singapore 2021

   Abs HTML

   In an automated container terminal, the handling of containers is accomplished through the coordination of multiple material handling equipment. The transportation of containers between the berth and the storage yard, traditionally done by prime movers, is now carried out by the Electric Automated Guided Vehicles (AGV). To accomplish the transportation of containers, these AGVs have to be routed carefully to avoid collision or deadlocks, and at the same time sent for recharging to maintain sufficient battery charge. An efficient AGV fleet management relies on an optimal charging facility and operational planning, which includes routing and scheduling of the recharging operations. There are however practical challenges that arise mainly due to the limited charging stations, short planning period and the sheer scale of the system. In this thesis, the battery management at the facility and operational planning levels are studied together with a fast dynamic routing for a large AGV fleet, with the aim of optimising the terminal operations. Firstly, the planning of charging facility is studied with the aid of a simulation model under different configurations and scenarios. Then, the recharging scheduling for the AGV fleet under a rolling horizon planning is tackled using the proposed multi-agent reinforcement learning approach. This problem is extended to the dynamic planning context, where job assignment is carried out dynamically. Finally, a fast deadlock-free dynamic routing is examined under capacitated network, particularly for systems with a large AGV fleet. The research presented highlights the success of the proposed approach and the benefits of efficient AGV management on the terminal performance.

2. Journal

   Simulation model and performance evaluation of battery-powered AGV systems in automated container terminals

   Simulation Modelling Practice and Theory 2021

   Abs HTML

   The use of battery power is becoming widespread rapidly among the mega ports worldwide, owing its low emission and high energy efficiency. In this paper, a simulation approach is presented to configure the charging stations (CSs) and battery-powered automated guided vehicles (B-AGVs) at automated container terminals. The facility planning of the CSs and the operation strategies of the B-AGVs are crucial for the system performance of the terminal. A port system is modeled as a discrete event simulation model, mainly consisting of three parts: vessel generator, dispatcher, and traffic network. Two types of layout designs and two types of recharging policies are presented, to deploy the CSs and control the B-AGVs to be recharged, respectively. Extensive simulation experiments are conducted to analyze the parameter effects on the system performance. The results indicate that a decentralized CS layout and a progressive recharging policy lead to excellent performance. Some management insights are offered to gain a better understanding of the key factors when deploying a B-AGV system.

3. Journal

   A data-driven business intelligence system for large-scale semi-automated logistics facilities

   International Journal of Production Research 2021

   Abs HTML

   With the proliferation of e-commerce, the regional hub of a large-scale logistics company is required to sort and load a large number of packages into different delivery vehicles by dawn and deliver them to customers by noon on a daily basis. The efficiency of the sorting operation is thus a competitive advantage which directly impacts the company’s service level. In this study, a data-driven business intelligence system for the semi-automated sorting facility is proposed for real-world implementation. To determine the cargo handling sequence, an information-based approach with a multi-criteria index function is developed. Then a simulation-based optimisation framework, which integrates a multi-objective search algorithm with a simulation model, is employed to fine-tune the parameters of the index function to perform optimally. The results of the numerical experiment show that the proposed technique is able to reduce 20% of the sorting operation duration, which equals a reduction of about 3600 man-hours per year. The study is a good example of applying emerging technologies in the logistics industry.

2018

1. Conference

   Challenges and opportunities in integration of simulation and optimization in maritime logistics

   In 2018 Winter Simulation Conference (WSC) 2018

   Abs HTML

   Maritime logistics plays an important role in the global trading scene with over 80% of global trade by volume and more than 70% of the trade value being handled by vessels and seaports worldwide. Today, the maritime industry is facing both new challenges and opportunities. Amongst the existing review papers, an in-depth and systematic summary on the integration of simulation and optimization is lacking. To fill the gap, this paper reviews dozens of papers on the integration of simulation and optimization for maritime logistics since 2010. Five modes of integration are classified according to how the two techniques interact with each other. Lastly, the paper introduces new challenges and opportunities in the maritime industry, and how the integration of simulation and optimization can help to boost the development of the next generation maritime systems.

2017

1. Conference

   Information based approach for sort operation in logistic industry

   In 2017 13th IEEE Conference on Automation Science and Engineering (CASE) 2017

   Abs HTML

   With the explosive increase of e-commerce in Singapore, a world-leading logistic company has to sort thousands of packages to specific vehicles before dawn and then deliver to customers by noon every day, and thus, the operation efficiency becomes the key competitive indicator. As in the era of Industry 4.0, we aim to explore and utilize the data passing through the operations to improve the package sorting operation, which currently is purely based on First-Come-First-Serve strategy. Upon observation of the current operation, there are two major challenges, which are to: (1) reduce the sort operation duration, effectively reducing under-utilization of workstations and personnel, and to (2) minimize the waiting time for route fulfilment in order to reduce congestion at the loading bay. To tackle the problem, this study proposes an information based approach to determine the handle sequence of ULDs based on three metrics: the ULD ready time, the ULD processing time, and the ratio of the packages to routes on standby. The numerical experiment has shown that the proposed approach shaves off 10% of the sort operation duration, which equates to an annual reduction of about 2500 man-hours.