Shuaian Wang

Fundamental properties and pseudo-polynomial-time algorithm for network containership sailing speed optimization

In container liner shipping, bunker cost is an important component of the total operating cost, and bunker consumption increases dramatically when the sailing speed of containerships increases. A higher speed implies higher bunker consumption (higher bunker cost), shorter transit time (lower inventory cost), and larger shipping capacity per ship per year (lower ship cost). Therefore, a container shipping company aims to determine the optimal sailing speed of containerships in a shipping network to minimize the total cost. We derive analytical solutions for sailing speed optimization on a single ship route with a continuous number of ships. The advantage of analytical solutions lies in that it unveils the underlying structure and properties of the problem, from which a number of valuable managerial insights can be obtained. Based on the analytical solution and the properties of the problem, the optimal integer number of ships to deploy on a ship route can be obtained by solving two equations, each in one unknown, using a simple bi-section search method. The properties further enable us to identify an optimality condition for network containership sailing speed optimization. Based on this optimality condition, we propose a pseudo-polynomial-time solution algorithm that can efficiently obtain an epsilon-optimal solution for sailing speed of containerships in a liner shipping network.

Mathematically calculating the transit time of cargo through a liner shipping network with various trans-shipment policies

ABSTRACT This paper derives the mathematical expressions for the transit time of cargo through a liner shipping network. Main efforts are devoted to deriving the calculation expressions of the connection time of cargo during trans-shipment. For the forward and many-to-one trans-shipment policies, we conduct a minor correction towards the expressions in existing studies to improve the completeness. Meanwhile, we propose an alternative but more straightforward calculation method for connection time which bypasses the complicated inductive argument in existing studies. Then we introduce two new trans-shipment policies: backward trans-shipment and one-to-many trans-shipment, and mathematically calculate the corresponding connection times. Numerical experiments also deliver some managerial insights into the effectiveness of backward trans-shipment in transit time control.

Station choice for Australian commuter rail lines: Equilibrium and optimal fare design

We examine how park-and-ride commuters living along a rail line compete for seats when they travel to their workplace in Australian metropolitan areas. First, we prove that at user equilibrium in which each commuter minimizes her expected travel cost, there exists one station on the rail line at which some commuters could find a seat and the others have to stand; all of the commuters boarding at its upstream stations have seats and all of the commuters boarding at its downstream stations must stand in the train. We derive a solution algorithm for obtaining a user equilibrium, which involves solving an equation with only one variable. We demonstrate that more than one user equilibrium may exist. Second, we examine the system optimal station choice that assumes all of the commuters cooperate and minimizes their total travel cost. An analytical solution approach is proposed based on the structure of the problem. Third, we investigate the optimal train fare design that leads to the system optimal station choice. We prove that the optimal train fare satisfies: there exists a particular train station that has some seats and the train is full after this station. All of its upstream stations have the same fare, which is higher than or equal to the fare of this particular station; and all of its downstream stations have the same fare, which is lower than the fare of this particular station.

Analysis of the development potential of bulk shipping network on the Yangtze River

ABSTRACT In the past decades, a multilayer transshipment network of bulk shipping has been formed along the Yangtze River so as to support the fast development of Chinese iron and steel industry. Yet with the decrease of iron ore trade in China since 2014, the bulk port system on Yangtze River probably will be subject to change in the future. Under this background, this paper aims to analyze the development potential of Yangtze River bulk ports system with a focus on iron ore transshipment. To realize this objective, we firstly sort out the main transshipment patterns of bulk shipping, and optimize the bulk-shipping network with an optimization model. Several scenarios are then proposed and examined in the model by changing corresponding parameters. Cooperation among ports as one scenario is analyzed by applying core theory in cooperative game. Based on the changes of transshipment plans observed under the various scenarios, we finally ascertain the different development potentials of the system, and provide suggestions to the port operators and local maritime authorities.

Cruise shipping review: operations planning and research opportunities

Purpose This paper aims to conduct a review on cruise shipping and the cruise shipping industry. The current trends are analyzed for the industry, showing that this industry is still young and has great potential to boom. Meanwhile, the Asia market is the fastest growth region among the global, to which increasing cruise ships are repositioned by major cruise lines. However, for such a promising industry, the literature review on some state-of-the-art research works suggests that the research works that have been conducted for the cruise shipping are quite limited, and the majority of the works belongs to empirical and descriptive studies, which does not provide optimization-based quantitative analysis on some operation planning problems. Design/methodology/approach This paper conducts a review on cruise shipping and the cruise shipping industry. Findings In reality, there are some important operation planning problems faced by cruise lines or cruise ships, and four of them are addressed in this paper in response to the fast growing trend. The addressed operation planning problems are cruise fleet management, cruise ship deployment, cruise itinerary design and cruise service planning. Originality/value The importance and the attention for the research on the problems are also elaborated in the paper.

Formulating cargo inventory costs for liner shipping network design

ABSTRACT This study examines how to incorporate the inventory costs of containerized cargoes into existing liner service planning models such that the designed networks could be improved while not causing extra modeling/computational burden. Two approaches are compared: (i) not considering the inventory costs at all and (ii) incorporating the inventory costs associated with onboard time and those related to transshipment by assuming a fixed connection time. The two models are compared with the ideal model capturing the exact inventory costs on a route choice problem and a capacity planning problem based on extensive randomly generated and practical numerical experiments. The results show that: first, ignoring the inventory costs in service planning models may lead to network design with much higher costs (poor network design decisions); second, in service planning models assuming weekly frequency, the inventory costs associated with onboard time could be formulated exactly, and those related to the connection time of weekly services could be approximated by assuming fixed connection time of 3.5 days for ports with 1 day’s minimum connection time and 4.5 days for ports with 2 days’ minimum connection time.

Mixed-Integer Linear Programming on Work-Rest Schedule Design for Construction Sites in Hot Weather

An appropriate design of work-rest schedule is recognized as an efficient way in providing betteri¾?ergonomici¾?environment, improving labor productivity as well as safety. Construction workers usually undertake physically demanding tasks in an outdoor environment, with awkward postures and repetitive motions. This study proposes a mixed-integer linear programming approach to optimize the work-rest schedule for construction workers in hot weather for the objective of maximizing the total productive time. The model takes into consideration the physical and physiological conditions of the workers, the working environment, the nature of the jobs and the minimum rest duration of the government regulation. The results of numerical experiments show that the proposed model outperforms a default work-rest schedule by up to 10% in terms of total productive time. This implies considerable cost savings for the construction industry.

Mixed-Integer Linear Programming Models for Teaching Assistant Assignment and Extensions

In this paper, we develop mixed-integer linear programming models for assigning the most appropriate teaching assistants to the tutorials in a department. The objective is to maximize the number of tutorials that are taught by the most suitable teaching assistants, accounting for the fact that different teaching assistants have different capabilities and each teaching assistantźs teaching load cannot exceed a maximum value. Moreover, with optimization models, the teaching load allocation, a time-consuming process, does not need to be carried out in a manual manner. We have further presented a number of extensions that capture more practical considerations. Extensive numerical experiments show that the optimization models can be solved by an off-the-shelf solver and used by departments in universities.

Optimal reefer slot conversion for container freight transportation

ABSTRACT Given a fleet of container ships of varying capacity, a cost-efficient approach for improving fleet utilization and reducing the number of delayed containers is to optimize the sequence of container ships in a given string, a problem which belongs to the large ship-deployment class. A string sequence with ‘uniformly’ distributed ship capacity is more likely to accommodate a random container shipment demand. The number of one’s total ship slots acts as a gauge of the capacity of the container ships. Meanwhile, there are two types of ship slots: dry slots and reefer slots. A dry slot only accommodates a dry container, while a reefer slot can accommodate either a dry or a reefer container. The numbers of dry and reefer slots for ships in a string are different. Therefore, in this study, we propose a model that considers both dry and reefer slots and use it to elucidate the optimal ship-deployment sequence. The objective is to minimize the delay of dry and reefer containers when the demand is uncertain. Furthermore, based on the optimal sequence deduced, the study also investigates the need to convert some dry slots to reefer slots for the container ships.

Tug scheduling for hinterland barge transport: A branch-and-price approach

In a hinterland barge transport system, barges are usually not self-propelled and need to be towed or pushed by tugs. This study investigates a tug-scheduling problem at a seaport that is located at a river mouth and that connects the hinterland ports along the river with the global maritime transportation network. A mixed-integer programming model is proposed to optimize the assignment of barges to tugs as well as the time when the tugs depart from the seaport and go to the hinterland ports. Some properties of the model are also investigated. Moreover, an exact solution method based on a branch-and-price approach is developed to solve the proposed model. Numerical experiments are also conducted to validate the effectiveness of the proposed model and the efficiency of the proposed solution method.