The operation of Autonomous Underwater Vehicle(AUV)mainly carries out underwater ocean exploration and ocean operations.Therefore,it is necessary to realize AUV diving and surfecing fast.The process of AUV diving is a complex maneuvering motion,which influences the AUV's safety.A ordinary diving process includes three stages:1)control the trim to prepare for diving;2)diving in steady state;3)control the trim to prepare for cruising at the givendepth.It is beneficial to the AUV diving and surfing motion with high maneuverability to predict the motions accurately.Thus,this paper developed a physics-based numerical simulation method to model the AUV diving by self-propulsioa To make the complex simulationto be achieved and verified,the simulation pro cesses included three associated parts:Firstly,the towing diving of AUV with a stationary propeller was modeled.The fully appended AUV with rudders and propeller was modeled.A multi-block hybrid dynamic grid was built to mesh the domain which combined trim,roll,surge and dive motions.A pre-defined motion was used to model the AUV towed diving.The AUV's forces and flow field characters were obtained.During this process,the propeller acted as a resistance source.And the drag of AUV decreased from the largest to the smallest and at last turned to steady as the flow field became unstable to stable from the initial time to the end time.Secondly,the forced diving of AUV with a rotating propeller was modeled.The original model and mesh was used.A dynamic zone method is built which can model the motions combined propeller rotating,AUV trim,surge and dive.The coupled motion parameters were programmed.Then the forced diving was performed.During this process,the propeller acted as a thrust part.The change of the flow field from the unstable to the stable makes the AUV resistance decreases and until it reached a constant value.Thirdly,the free diving of AUV by self-propulsion was modeled.The AUV was pushed to dive by a rotating propeller from stationary to an acceleration state.During this process,the UDF(User Defined Functions)is built,where the thrust of propeller was transferred to the AUV,The RANS(Reynolds Averaged Navier-Stokes)equation and six degree of the function were solved.The acceleration of AUV was obtained and integrated to get the AUV velocity.The Velocity of AUV was delivered to the propeller,which changed the inflow the propeller and the thrust by the propeller re-generated.This process iterated and repeated,until the thrust and resistance was equal,when the velocity turned to stable.Then the calculation was ended.The steady velocity of 1.5m/s was obtained with a constant 600RPM.The comparison of the AUV resistance during the three simulations verified the practicability of the physics-based simulation of AUV diving by self-propulsion.It is also demonstrated that the practicability of the multi-block hybrid dynamic mesh presented.This study could provide a physics-based simulation method for more complex maneuvering motion of AUV in the future. |