Numerical Predictions of Hydrodynamic Forces and Squat of Ships in Confined Waters

Due to the blockage effects in the flow, hydrodynamic performances of a ship in confined waterways are significantly different from those in deep waters. In particular, the hydrodynamic interactions between ship hull and sea bottom or bank wall in the vicinity tend to be more complicated. This gives rise to notable increases in hydrodynamic forces on the hull, along with more pronounced dynamic sinkage and trim where the ship squat phenomenon occurs. The predictions of hydrodynamic forces and ship squat are of great importance from the safe navigation point of view and are also challenging because of the remarkable viscous effects and flow separations in confined waters. In this paper, an unsteady Reynolds-Averaged Navier Stokes (URANS) solver is applied to simulate the viscous flows around a tanker and a container ship in a confined canal, which is characterized by both shallow sea bottom and close side bank. In each case, the ship is moving along a straight course. The free surface elevation caused by the ship motion is captured by the Volume of Fluid method. In all simulations, the ship position during the motion is updated at each time step according to the computed hydrodynamic forces acting on the hull, from which the dynamic sinkage and trim of the ship is determined. A grid dependency study is performed so as to estimate the numerical error resulted from the grid discretization. The influences of water depth, ship-to-bank distance, ship speed and ship hull form on the hydrodynamic forces and squat of the ship are investigated through systematic computations. Numerical results are evaluated in combination with available experimental data. For the squat, additional data from a mathematical model are used for comparison. The hydrodynamic performances of the ships are generally in good agreement with the data. Furthermore, the mechanisms of the shallow water effects and bank effects involved in the confined waters are analyzed from the simulated flow field around the hulls.