Study On The Maneuverability Of Twin Tail Semi-Submerged Unmanned Vehicle Near Free Surface

The underwater vehicle are widely used in civil,military and commercial because of its great maneuverability,stealth and reliability.The majority of the working conditions of the underwater vehicle are in deep water area.But in some cases,such as being deployed and reclaimed from platform and rising to the free surface for GPS location,the submersible will sail in near free surface.Under these circumstances,the hydrodynamic forces acting on the submersible are different from those in deep water area.Therefore,it is necessary to study the hydrodynamic performance of the underwater vehicle near the free surface.And the maneuverability is one of the most important performances of the submersible.So,it is of great significance to study the maneuverability of the submersible near the free surface.The paper is based on a new type twin tail semi-submersible unmanned vehicle and the maneuvering performances of this unmanned vehicle near free surface are investigated using CFD software STAR-CCM+ based on the FVM.The following works have been completed in this paper:Firstly,as the simplest submerged body model,the axisymmetric underwater body is used in the present work.The straight line motion,oblique running motion and movement in six degrees of freedom of the axisymmetric underwater body near free surface are simulated in order to compare hydrodynamic forces and moments obtained in CFD calculations with the data in other papers to verify the accuracy of the CFD calculations and to obtain a preliminary understanding of the interaction mechanism between the axisymmetric underwater body and the free surface.In the meantime,to lay the foundation for the calculations of the maneuverability of twin tail semi-submerged unmanned vehicle near free surface.Then,the calculations of the twin tail semi-submerged unmanned vehicle near free surface are carried out.The calculations of straight line motion are carried out for several different parameters,including velocity variations from 4 kn to 6 kn,and different draft from 600 mm to 1000 mm.The calculations of the semi-submerged vehicle sailing with different drift angles from 2° to 6° are also carried out.The hydrodynamic forces and moments in different circumstances are obtained and the hydrodynamic performances of the semi-submerged vehicle vary with different velocity,draft and drift angle are discussed.In the end,the calculations of the movement in six degrees of freedom of twin tail semi-submerged unmanned vehicle near free surface are carried out.The motions such as pure sway,pure yaw,pure heave and pure pitch in fixed velocity(4 kn),different draft(600mm,800 mm and 1000mm)and motion frequency(0.4Hz and 0.5 Hz)are simulated.The lateral forces and yaw moments acting on the semi-submerged vehicle in pure sway and pure yaw,as well as the vertical forces and trim moments in pure heave and pure pitch change with different draft and motion frequency are analyzed.And different hydrodynamic coefficients are calculated.Furthermore,the rotary motion responses of twin tail semi-submerged unmanned vehicle are studied by applying two forces on the twin tails.