Ship Hydrodynamics in Confined Waterways

Abstract

The hydrodynamic performance of a vessel is highly dependent on its maneuvering waterways. The existence of the banks and bottom, as well as the presence of the other vessels, could have a significant influence on a ship's hydrodynamic behavior. In confined waterways, many researchers suspect the applicability of the classical potential flow method because of its nonviscous and irrotational assumption. The main objective of the present article is to improve and develop the boundary value problem (BVP) of a potential flow method and validate its feasibility in predicting the hydrodynamic behavior of ships advancing in confined waterways. The methodology used in the present study is a 3D boundary element method based on a Rankine-type Green function. The numerical simulations are performed by using the in-house developed multibody hydrodynamic interaction program MHydro. The waves and forces (or moments) are calculated when ships are maneuvering in shallow and narrow channels, when ships are entering locks, or when two ships are encountering or passing each other. These calculations are compared with the benchmark test data published in MASHCON, and the published computational fluid dynamics results. It has been found that the free-surface elevation, lateral force, and roll moment can be well predicted in ship-bank and ship-bottom problems. However, the potential flow solver fails to predict the sign of the yaw moment because of the cross-flow effect. When a ship is entering a lock, the return-flow effect has to be considered. By adding a proper return-flow velocity to the BVP, the modified potential flow solver could predict the resistance and lateral forces very well. However, it fails to predict the yaw moment because of the flow separation at the lock entrance. The potential flow method is very reliable in predicting the ship-ship problem. The resistance and lateral force, as well as the yaw moment, can be predicted well by using the potential flow method.