Direct Simulations Of Ship Maneuver Using Overset Grid Technique

With the boosting of high performance computing and developments of numerical methods,Computational Fluid Dynamics(CFD)has been widely used in the research field of naval architecture and ocean engineering.Among several concerned hydrodynamic problems,ship maneuveriability is one of the most complex problems in the research of ship hydrodynamics.When considering ship maneuver in waves,it becomes the one of the most challenging issues since it involves the performance of ship resistance,propulsion,seakeeping and maneuvering.In general,it is very close to the real world condition and making it with a great prospect for the applications in ship and ocean engineering.So far,the most challenging problems are as follows: first is the complex coupling motion with the ship hull-propeller-rudder system,another one is the maneuvering control and large amplitude motions,as for maneuvering in waves,the tool should have the ability to solve the low frequency maneuvering motion and high frequency wave induced motion simultaneously.The objective of this dissertation is to develop the maneuvering control module based on the in-house code naoe-FOAM-SJTU,with the purpose of extending its ability in simulating various ship maneuvers.In addition,this paper has also modified the wave generation module,which makes it possible to numerically investigate the self-propelled ship maneuver in waves.Within the implementation of maneuvering control module,the paper adopts a feedback control mechanism with respect to the ship motion.Based on the overset grid technology,heading control,zigzag and turning circle maneuver control module are developed to directly simulate the free running ship maneuver.As for the wave generation module,the paper have combined the present naoe-FOAMSJTU solver with the open source third-party wave generation tool waves2 Foam,which can make full use of the relaxation zone and can generate desired waves with moving computational domain.So far,it has been proved to be reliable and robust in simulating ship maneuver in regular waves.In order to validate the developed maneuvering control module and improved naoeFOAM-SJTU solver,three categories of validation cases including planner motion mechanism(PMM)tests,free running ship maneuver in calm water and various waves are performed.The first validation case is the simulation of PMM tests,where the static drift,pure sway and pure yaw test are computed.Through the static and dyanmic test,the solver is proved to be reliable in simulating the large amplitude maneuvering motion.The second category is the self-propelled ship maneuvers with direct rotating propellers and moving rudders.The fully appened twin screw ONR Tumblehome ship model is used for the selfpropulsion calculation and the free running maneuver in calm water.In the free running maneuver in calm water case,standard 10/10,20/20 zigzag maneuver and turning circle maneuver are performed.In the third category,the free running ship maneuver in regular waves are directly simulated.The validation cases include the course keeping simulations in head waves,bow quartering waves and beam waves,as well as the free running ship zigzag maneuver in various wave conditions,where different wave length and wave heights are calculated to investigate the wave effects on the free running ship maneuver.Turning circle maneuver in waves is also investigated.The rudders and propellers are fully discretized by overset grids in all the validation cases.These rotating propellers and moving rudders are able to move with respect to the ship motions and itself can move according to the specified maneuvering control.The numerical results of the maneuvering parameters are compared with the available experiment measurements and the comparisons show good agreements,which indicate that the present developed maneuvering control module and the wave module can be reliable and robust in handling with free running ship maneuver in both calm water and regular waves.The application areas in ship hydrodynamics have been greatly expanded using the present numerical approach.