When a ship is navigating on water surface, its resistance can be divided into three components: frictional resistance, eddy resistance, and wave-making resistance (Havelock, 1909). While in many cases, the steady component dominates the wave-making resistance, there are still certain instances where unsteady effects cannot be ignored. For example:
• Sudden changes of boundaries, such as the width and depth of the waterway. This may occur when ships navigate in port, harbor or lock environments. It will potentially increase the risk of collisions or grounding incidents.
• When a ship is overtaking (or being overtaken) or passing other vessels in busy waterways, the unsteady effects of the free surface can generate horizontal unsteady forces between the two ships. This can result in collisions between the vessels and lead to the blockage of the waterway.
• Another typical scenario is when a ship keeps accelerating in open area,
particularly in extremely shallow depths. In this case, the unsteady effects will
significantly increase after the ship’s velocity exceeds the critical speed. At this point, the unsteady effects alter the flow field around the ship, resulting in
changes in wave-making resistance.
This thesis posits that the aforementioned unsteady effects are closely correlated with unsteady waves on the free surface. Hence, the primary objectives of this research are two-fold:
1) To develop a linear unsteady numerical program which is capable of simulating the unsteady free surface effects. This program will accurately capture the formation and evolution of unsteady waves.
2) To devise a real-time updating mesh method that handles changes in waterway boundaries and depths encountered during the simulation process. Additionally, it ensures temporal continuity for all cells on the free surface.
In this thesis, Chapter 1 will be an introduction and literature review of the research topic. Chapter 2 introduces the methodology used in this research. Chapters 3 to 5 constitute the main body of this thesis. Specifically, Chapter 3 presents the simulation of unsteady waves generated by a single object, with particular focus on the simulation of the previously mentioned scenario of a ship accelerating in shallow water. Chapter 4 aims to simulate multiple objects. In this chapter, the ship-to-ship problem and the unsteady bank effect within a confined waterway will be investigated. Due to the presence of interacting objects, the grid is required to be updated in real-time to accommodate changes in the boundary conditions. The simulation results
will be compared with experimental data to validate their accuracy. Chapter 5 will build upon the foundation established in Chapter 3 by extending the grid handling techniques to account for unsteady banks. Additionally, the unsteady hydrodynamic model developed in Chapter 2 will also be incorporated. This integration will enable the simulation of the intricate wave phenomena that occurs during the process of a vessel entering a lock. The simulation results will be compared against experimental data as well as computational fluid dynamics (CFD) results to validate their accuracy. This comparative analysis serves to ensure the reliability and fidelity of the simulation outcomes. By undertaking these efforts, Chapter 4 aims to provide a comprehensive
understanding of the wave behaviour within the lock chamber during vessel entry, contributing to the advancement of knowledge in the field of unsteady water dynamics. Finally, Chapter 6 serves as the conclusion which summarizing all the achievements of this thesis and also proposing future directions for research.When a ship is navigating on water surface, its resistance can be divided into three components: frictional resistance, eddy resistance, and wave-making resistance (Havelock, 1909). While in many cases, the steady component dominates the wave-making resistance, there are still certain instances where unsteady effects cannot be ignored. For example:
• Sudden changes of boundaries, such as the width and depth of the waterway. This may occur when ships navigate in port, harbor or lock environments. It will potentially increase the risk of collisions or grounding incidents.
• When a ship is overtaking (or being overtaken) or passing other vessels in busy waterways, the unsteady effects of the free surface can generate horizontal unsteady forces between the two ships. This can result in collisions between the vessels and lead to the blockage of the waterway.
• Another typical scenario is when a ship keeps accelerating in open area,
particularly in extremely shallow depths. In this case, the unsteady effects will
significantly increase after the ship’s velocity exceeds the critical speed. At this point, the unsteady effects alter the flow field around the ship, resulting in
changes in wave-making resistance.
This thesis posits that the aforementioned unsteady effects are closely correlated with unsteady waves on the free surface. Hence, the primary objectives of this research are two-fold:
1) To develop a linear unsteady numerical program which is capable of simulating the unsteady free surface effects. This program will accurately capture the formation and evolution of unsteady waves.
2) To devise a real-time updating mesh method that handles changes in waterway boundaries and depths encountered during the simulation process. Additionally, it ensures temporal continuity for all cells on the free surface.
In this thesis, Chapter 1 will be an introduction and literature review of the research topic. Chapter 2 introduces the methodology used in this research. Chapters 3 to 5 constitute the main body of this thesis. Specifically, Chapter 3 presents the simulation of unsteady waves generated by a single object, with particular focus on the simulation of the previously mentioned scenario of a ship accelerating in shallow water. Chapter 4 aims to simulate multiple objects. In this chapter, the ship-to-ship problem and the unsteady bank effect within a confined waterway will be investigated. Due to the presence of interacting objects, the grid is required to be updated in real-time to accommodate changes in the boundary conditions. The simulation results
will be compared with experimental data to validate their accuracy. Chapter 5 will build upon the foundation established in Chapter 3 by extending the grid handling techniques to account for unsteady banks. Additionally, the unsteady hydrodynamic model developed in Chapter 2 will also be incorporated. This integration will enable the simulation of the intricate wave phenomena that occurs during the process of a vessel entering a lock. The simulation results will be compared against experimental data as well as computational fluid dynamics (CFD) results to validate their accuracy. This comparative analysis serves to ensure the reliability and fidelity of the simulation outcomes. By undertaking these efforts, Chapter 4 aims to provide a comprehensive
understanding of the wave behaviour within the lock chamber during vessel entry, contributing to the advancement of knowledge in the field of unsteady water dynamics. Finally, Chapter 6 serves as the conclusion which summarizing all the achievements of this thesis and also proposing future directions for research
