Numerical Calculation Of Hydrodynamic Forces On A Ship In The Oblique Motion With Shallow Water And Bank Effects

The modern ship is going through a trend of developing into the large-sized ship.On the other hand,many of the existing ports and inland channels in China have insufficient water depth.Studies have shown that when the ratio of water depth to draft is less than 3,shallow water effect will occur.Ships sailing in shallow water are easily faced with "squat" due to the impact of blocking effect and asymmetric flow,which has the danger of bottoming.In addition,the shallow water effect will lead to the increase of resistance,decrease of speed,deterioration of rudder effect,decrease of turning ability,running-away rudder angle and other adverse effects.Therefore,it is of great importance for the rational manipulation and control of the ship and safety of the sailing ship to research on hydrodynamic characteristics of ship in shallow water.In recent years,with the continuous development of computer technology and improvement of numerical methods,numerical simulation method based on computational fluid dynamics(CFD)has been widely used in the studies on ship's hydrodynamic.Based on RANS equation,this paper calculates the hydrodynamic of KVLCC2 ship in oblique motion for the shallow water and bank effects.The turbulence is modeled by RNG k-s turbulence model,and hexahedral grids are adopted.Considering that the Froude number is less than 0.1,the calculation ignores the effect of free surface elevation.First,it conducts numerical simulation on KVLCC2 ship model in straight and oblique motion in the deep water and calculates the hydrodynamic forcing on hull.In order to evaluate the credibility of the numerical results,in accordance with ITTC-Recommended procedures for uncertainty analysis in CFD,it imposes verification and validation on its numerical results of hydrodynamic.The mainly examination includes iteration convergence analysis and grid convergence study.This paper designs three sets of grid to carry out analysis on grid convergence,with the grid refinement ratio of rG=(?).Then this paper uses the numerical method to calculate the straight and oblique motion of hull of KVLCC2 under the circumstance of shallow water and bank effects and make verification and validation of the numerical hydrodynamic results.Through verification and analysis,this paper assesses numerical error and numerical uncertainty,and makes validation analysis to evaluate comparison error and validation uncertainty by analyzing experimental data.Finally,influences of water depth,channel wall and drift angles on hydrodynamic forces and flow field around are analyzed.It can be concluded that CFD numerical method used in this paper can reasonably predict the ship hydrodynamics in oblique motion in shallow water.The change mechanism of ship hydrodynamics in oblique motion in shallow water,which this paper discovered,has a reference value for the studies on the ship maneuverability in restricted waters.In addition,the summary of influence of various factors on the ship hydrodynamics can provide a reference for navigators and waterway designers.