Numerical Calculation Of Hydrodynamic Forces On A Ship With Straight Motion In Sloping Bottom Waters

The modern ship is going through a trend of developing into the large-sized ship.With the continuously increasing of the main dimensions of the ship,many ports and coastal waters are narrow relatively,which become restricted waters of ship sailing.Although the sloping bottom waters are common restricted waters,there are few experimental and numerical studies.When navigating in sloping bottom waters,the hydrodynamic forces acting on the ship are quite different from infinite waters.It is shown that the sloping of the bottom affects the flow field around the ship,and the ship will be subjected to the additional lateral force and the yaw moment.This is an unsafe factor for navigating and has the risk of collision and grounding.Therefore,it is of great significance to study the hydrodynamics of the ship sailing in the sloping bottom waters.In recent years,with the development of computer science and technology and the improvement of numerical methods,computational fluid dynamics(Computational Fluid Dynamics,CFD)based on viscous flow method is widely used in the research of ship hydrodynamics.In this paper,numerical simulation is carried out to study the viscous flow around the bare hull and the hull-propeller-rudder system in the sloping bottom waters by numerical solving the RANS equation.The RNG k-? model is adopted to simulate the turbulence and the multi-reference system model(MRF)is adopted to propeller rotating.The validity of this numerical method is verified by simulating the flow around the bare hull sailing straightly in the flat bottom waters.The verification also concerns the iterative convergence and convergence of the grid scale,and the comparison with the experimental results.Then this numerical simulation method is used to calculate the hydrodynamic forces of the ship sailing straightly in the sloping bottom waters.In this paper,the cause of the hydrodynamic forces acting on the ship in the sloping bottom waters is revealed and the influences of the water depth and the bottom slope on the ship hydrodynamic forces are analyzed.Based on the analysis of simulation results,the hydrodynamic forces acting on hull-propeller-rudder system sailing straightly with different steering angle are further calculated in a specific sloping bottom waters,and the influence of the rudder angle on the hydrodynamic forces of the ship in the sloping bottom waters is analyzed.The influence of the propeller and rudder on the flow field around the ship is also analyzed by comparing the flow field of the bare hull and the hull-propeller-rudder system.The numerical method used in this paper can predict the hydrodynamic forces of the ship navigating in the sloping bottom waters.The variation characteristics of the ship hydrodynamics sailing straightly in the sloping bottom water is obtained,which has a certain reference value for the safe navigation,navigation management and channel design to the restricted waters.