Thesis

Hydrodynamic interactions among ships moving in a single-file formation

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Awarding institution
  • University of Strathclyde
Date of award
  • 2025
Thesis identifier
  • T17232
Person Identifier (Local)
  • 202050266
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Qualification Name
Department, School or Faculty
Abstract
  • To minimize energy expenditure for each individual, animals adopt distinctive formations,such as fish schooling, ‘V’ formation by flying birds, and single-file formation by waterfowls. The phenomenon of ducklings following their mothers in a single-file configuration has been revealed by the mechanism of wave-riding and wave-passing. Drawing inspiration from this phenomenon, an investigation is undertaken on ships moving in a single-file formation. This thesis explores two scenarios: ships advancing on calm water without connections and ships advancing in waves with connections (marine trains). An in-house code, MHydro, based on potential flow theory, is developed to analyze the wave-making and seakeeping problems. Additionally, a series of experimental tests are conducted to investigate the complex interference between ships moving on calm water. Firstly, the wave drag and wave patterns of ships in a single-file formation on calm water are examined using MHydro. It is found that when constructive wave interference occurs in a two-ship formation, the wave resistance of the trailing ship increases and the leading ship experiences a decrease in its wave drag, especially when the two ships are in close proximity. Mutual benefit arises when destructive wave interference occurs between two ships. In addition, increasing the size of the trailing vessel facilitates the effect of wave-riding by leading ship, but this effect becomes less pronounced as the speed increases. In a multi-ship formation configuration, changing the size of the leading ship will have a localized effect on the wave-passing, but the fleet will eventually tend to a dynamic equilibrium. When the position of the first trailing vessel is changed, there is similarly a localized effect on the wave-passing. Adjusting the first trailing ship to the position of the constructive wave interference is not favorable to reduce its own drag but enhances the wave-riding effect of its close follower. Finally, to achieve wavepassing, the trailing ship does not necessarily have to occupy an optimum position. This can still be accomplished if the trailing ship moves backward by an integer multiple of wavelength. Next, a series of experiments are conducted to measure the total resistance of ships moving individually and in two-ship formations on calm water. The results indicate that the form of the bow has a more significant impact on the total resistance of single ships than the form of the stern. Specifically, the total resistance of a single ship with a transom stern is nearly identical to that of a ship with a sharp stern. However, ships with a flat bow exhibit significantly higher total resistance compared to those with a sharp bow. In a two-ship formation, the hydrodynamic pressure resistance of both the leading and trailing ships is significantly reduced when the gap between the two ships is small. This reduction occurs because the air hollow created by flow separation is filled by the bow waves of the trailing ship. When the trailing ship is positioned in the divergent-wave zone within the wake of the leading ship, wave interference between the two ships becomes the dominant factor influencing the variance in the total resistance of the trailing ship. As the gap between the two ships increases further, the wave interference weakens; however, the trailing ship still experiences a substantial reduction in resistance due to weakened flow separation and bubble drag reduction within the turbulent-bubble mixed flow region. Finally, the hydrodynamic responses of marine trains—ships connected together in a single-file formation—advancing in waves are investigated numerically. The slidinghinged connection is found to be the most suitable for marine trains, as it effectively avoids high vertical shear forces compared to rigid or hinged connections. Additionally, this connection type enables the entire ship formation to be powered by the leading ship. For marine trains consisting of five ships, the motion responses in heave and pitch increase significantly as the advancing speed increases. Changing the horizontal positions of the joints has minimal effect on the motion responses of each ship. Similarly, adjusting the gaps between the ships has a small impact on the motion responses from an engineering perspective, as the gaps between ships are generally not large.
Advisor / supervisor
  • Yuan, Zhiming
Resource Type
DOI

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