Simulations Of Ship Stopping Maneuver Using Overset Grid Technology

Recently,ships are becoming larger in order to improve transport efficiency and save costs.The crowded waterways and worse maneuverability of large ships will cause more collision accidents.Therefore,it is necessary to study stopping maneuverability to ensure the safety of ships.In this thesis,ship and offshore engineering hydrodynamic solver naoe-FOAMSJTU based on open source computational fluid dynamics software OpenFOAM and overset grid technology is used to simulate several stopping maneuvers of KVLCC2 model.Firstly,the maneuver of propeller reversing with no use of rudder is numerically simulated.The stopping parameters such as stroke and transverse distance are obtained and compared with the data of NMRI tank to verify the reliability of the numerical method adopted in this thesis.The thesis explains the cause of reversing effect through the analysis of the flow field.The right propelled flow is blocked by the stern,rising the pressure on the right aft of the ship,which pushes the stern to the left and turns the bow to the right.In addition,the influence of shallow water is considered in this thesis.By comparing the parameters and the flow field of stopping maneuver,it is found that the resistance of hull increases.Meanwhile,the wake velocity increases,making the reversing propeller more effective.So the longitudinal force and moment of Z direction acting on the ship is larger,leading to shorter stroke,less stopping time and larger turning angle of the ship in shallow water case.Then the maneuvers of propeller reversing with rudder turning are numerically simulated.It is found that turning the rudder to left while reversing the propeller will change the moving direction and reduce the longitudinal distance and time of stopping maneuver.Turning the rudder to right will increase the longitudinal distance and stopping time,while significantly reduce the transverse distance.The analysis of flow field shows that the reversing effect is reduced because the rudder behind the propeller blocks the forward flow.At the same time,the reverse propeller increases the fluid velocity after the ship,worsening the efficiency of rudder.After that,the maneuver of rudder turning with static propeller is numerically simulated.Through comparing the pressure distribution on the hull and the rudder,it is found that the existence of static propeller can be neglected.In this thesis,the KVLCC2 ship model with rudder is used and the simulation is carried on under three water depths.By comparing the stopping maneuver parameters and the flow field,it is found that the efficiency of rudder is worse in shallow water because the increasing wake velocity,resulting in poor effect of stopping maneuvering.So stopping maneuver with turning rudder in shallow water has larger stopping distance,longer stopping time and smaller turning angle.Finally,the maneuver of turning circle in deep and shallow water is numerically simulated.After analyzing and comparing the stopping parameters and flow field,it is found that the wake velocity in shallow water increases,worsening the effect of propeller and rudder.So the turning ability of the ship becomes worse in shallow water,which means larger diameter of turning circle.Then the parameters of various stopping maneuver predicted by the numerical method in this thesis is compared.If the ship needs to be completely stopped after stopping maneuver,the method of turning rudder to the left while reversing the propeller has minimum stopping distance and stopping time.While the method of turning rudder to the right has smallest transverse distance.The maneuver of turning circle can avoid crashing with minimum longitudinal distance and turning time.But there is still a large speed of ship when the maneuver is completed.The calculation results in this thesis can provide a reference for the selection of stopping maneuver,but the actual adopted method depends on the specific situation.