Numerical Simulation Study On Viscous Flow Field Of Ship Forced Rolling

When the ship is sailing on the sea,it will be affected by many kinds of forces and produce complex six-degree of freedom motion,among which rolling motion is the most commom and dangerous,so it is the most important in ship motion.For a long time,scholars all over the world have been devoted to the study of ship rolling.However,due to the obvious viscous effect,there is a great nonlinearity in the process of rolling,so it is not ideal to use the potential flow theory to study itAt present,scholars mainly focus on the prediction of the total rolling damping of the ship,but there is no detailed analysis of its components of it.Among them,as an important component of total rolling damping,eddy damping is closely related to the generation and dissipation of bilge vortex.Therefore,this paper will study the separation of flow,vortex motion and their mutual interference caused by strong viscous effect during forced rolling.In this paper,physical experiments and numerical simulation are combined to study the influence of rolling parameters on roll flow field.This study,firstly,based on OpenFOAM open-source software,RANS method,VOF method,moving grid technology and SST k-?turbulence model are used to simulate the forced rolling of ships.Then,the influence of roll period and roll amplitude on the roll flow field in two-dimensional case and the flow characteristics in large amplitude roll are discussed.Finally,the forced roll of three-dimensional ship model developed by the author's laboratory is introduced.The results of data processing are compared with the results of numerical simulation to prove the reliability of numerical simulation and study the influence of different rolling parameters such as speed on the three-dimensional ship rolling flow fieldThe results show that in the forced rolling flow field,the vorticity of the flow field increases with the increase of the rolling amplitude and decreases with the increase of the rolling period;In the case of large rolling,the inflow and outflow of bilge keel causes strong flow separation,and the complex interaction between vortices and results in the acceleration of vortex shedding speed and influence the position of vortex separation point;At the same speed,the larger the rolling amplitude is,the larger the vorticity of the flow field is;under the same rolling amplitude,the vorticity around the hull with speed is larger than that without speed,and the existence of speed makes the vortex move bakward,which makes the vortex obviously three-dimensional.The vortex motion and dissipation speed up,enhance the energy exchange between the hull and the surrounding fluid,and greatly increase the roll damping moment and coefficient.