Numerical Simulation Of Ship Roll Motions

The roll motion is one of the most common and dangerous ship motions occurring in winds and waves.Roll motions will result in the increase of wave loadings and ship drags,which lead to the decrease of the propulsion efficiency.Furthermore,large amplitude of roll motions may cause the capsizing.So,accurate simulations of ship roll motions have great importance for the research of the stability,maneuverability and safety.In the early years,the potential theory was used to study roll motions without viscosity into consideration,so the theory could not accurately compute roll motions.Now,with the development of technology,Computational Fluid Dynamics(CFD)are widely applied in the ship research,and it can be utilized to accurately simulate roll motions.This thesis simulated roll motions via solving incompressible Navierstokes equations by the naoe-FOAM-SJTU solver based on the OpenFOAM.The simulations included free decay roll and forced roll motions of 2D and 3D models with different roll amplitudes,frequencies and wave conditions.This thesis simulated forced roll motions of 2D ship model in different conditions first.Convergence study and validation was conducted to ensure the accurateness and reliability of meshes,Euler method and the solver.Then the damping moments divided into three parts——friction,vortex and wave moments.The influence of roll amplitude and frequency on these parts were analyzed.Next,based on the convergence study,the simulations of free decay roll and forced roll motions of 3D ship models with and without bilge keels were conducted in different conditions.The bilge keels and friction moments were separated from the total damping moments and the effect of roll amplitude on these parts were analyzed.Finally,ship roll motions on beam waves were simulated to analysis the effect of wave frequency on roll motions.