A comparative numerical study of bank effects on a cruise ship in crabbing motion based on URANS method

Abstract

The crabbing motion of a cruise ship perpendicularly towards a quay wall is investigated by an unsteady Reynolds-averaged Navier-Stokes (URANS) method. In the numerical simulations, the cruise ship is approaching the quay wall at a constant lateral speed and stops at a rather small ship-quay distance. The crabbing motion with multiple degrees of freedom is simulated by the dynamic overset mesh technique, while the free surface elevation is simulated by the Volume of Fluid method. To obtain reliable temporal discretization for the crabbing process, the time-step dependence study is conducted first, from which a suitable time step is determined. From the computations, the hydrodynamic performances of the cruise ship including: longitudinal force, lateral force, roll moment and yaw moment, as well as surge, heave, roll, pitch and yaw motions are predicted. To evaluate the importance of numerical models used in the URANS method, a comparative investigation is carried out to evaluate the impacts of boundary condition, turbulence model and temporal discretization scheme on the numerical results. From the comparisons, notable influences by the turbulence model and the temporal discretization scheme on both hydrodynamic quantities and flow field features can be observed, especially when the bank effects tend to be pronounced; while the boundary conditions are shown to be less significant. The numerical results indicate remarkable variations of the hydrodynamic quantities in the crabbing process under the influences of ship speed and bank effects. Given that the surge motion is one of the most principal crabbing performances, the initial drift angle with a set of deviations is also computed, coupled with two typical ship speeds in terms of practical navigation. It suggests that more attentions should be paid to the low-speed crabbing to minimize the surge variations. The present study demonstrates promising abilities of CFD methods to deal with the hydrodynamic predictions of harbour manoeuvres in restricted waters.