Numerical Study On Bank Effects For A Ship Sailing Along A Bank

In recent years, a continuous increase of the main dimensions of ships can be observed and because of that the problem of the effects of shallow and narrow channels on ship maneuverability becomes more and more serious. The hydrodynamic characteristic of ships sailing along bank in shallow and narrow channels is very different with that in infinite waterways. When a ship travels along a bank, the flow around the ship is asymmetric. As a result, a lateral force will act on the ship, directed towards the bank, as well as a yaw moment pushing her bow away from the bank, which are called bank effects. Bank effects are unsafe factors for ships moving near bank. If the ship-bank distance is very small, ship-bank collision may happen and that may cause casualties and property losses. Especially for VLCC, LNG, chemical vessel et al, the collision will also result in marine pollution and bring people huge disasters. Therefore, strengthening the research on bank effects to predict the maneuvering hydrodynamics for ships sailing along bank can guide the operation of ships to ensure the navigation safety and provide a reference to build channels with reasonable cross-section.In this thesis, a first-order 3D Rankine source panel method is applied to study bank effects and calculate the sway force and yaw moment acting on ships sailing along bank in shallow water. The velocity potential is represented by a Rankine source distribution on the hull surface, bank surface and free surface. The source strengths are determined by satisfying the boundary conditions on these surfaces. After the source strengths and the velocity potential are determined, the hydrodynamic pressure is obtained by Bernoulli equation and the hydrodynamic force and moment acting on the hull are calculated by pressure integral over the wetted hull surface. In the numerical procedure, the boundary condition on water bottom is satisfied by the method of images; the non-linear free surface conditions are satisfied by a scheme based on Newton iterative method; the radiation condition is satisfied by raised panels with staggered grid above the free surface.Applying the above panel method, the wave-making resistance and squat for Wigley hull and Series 60(CB=0.6) hull in deep water; the wave-making resistance and squat for Wigley hull in shallow water; the sway force, yaw moment and squat for Series 60 hull sailing along vertical bank, sloping bank and flooded bank as well as traveling off the center line of shallow narrow channels are obtained. The computational results are compared with available experiment results or the results by regression equations. The effects of ship-bank distance, water depth, speed, bank slope, the height of flooded bank and the width of shallow and narrow channel are analyzed. In the present research, through a lot of numerical practice, some experiences relating to the numerical schemes and arranging mesh are accumulated, that are useful for further research of ship maneuvering in restricted waterways.