Maneuverability Prediction Of Mini Underwater Vehicle Near Free Surface

The Mini Underwater Vehicle is very important in ocean exploitation on account of itscharacteristics such as small volume, low resistance, high stealth performance and goodmaneuverability. It needs to rise for navigation and localization after sailing some time. TheMini Underwater Vehicle is deployed and reclaimed from carrying platform. In theseconditions the Mini Underwater Vehicle sails near free surface. The flow environment is morecomplicated than limitless drainage area. The Mini Underwater Vehicle is easy to be disturbedby free surface because its small size and finite propulsion capability. Maneuverability is veryimportant to the Mini Underwater Vehicle, and the research of maneuverability is especiallymeaningful. In this paper, study about hydrodynamic performance of the Mini UnderwaterVehicle near free surface has been done, while the hydrodynamic coefficients in differentdepth are solved with computational fluid dynamics（CFD） method. Also the experiment ofmaneuverability near free surface is accomplished, and the motion characteristics can beobserved. The following work has been completed in this paper:1. The structural and unstructured mesh is gendered in different area to compute thehydrodynamic capability of the ellipsoid model and the Mini Underwater Vehicle whilesailing straight and with drift angle in limitless area. The hydrodynamic coefficients can bework out via simulation of movement in six degrees of freedom. The hydrodynamiccoefficients are also solved by experiment and Hess-Smith method. The results by CFD turnto be with good precision.2. The hydrodynamic performance is calculated in different depth of1.5times,2.5times,3.5times the maximum diameter of modules. The calculated modules contain the ellipsoidmodel, the streamlined model and the Mini Underwater Vehicle. The change of resistance,vertical force and trim moment versus depth and velocity is discussed. The reason of increaseof resistance is discussed. Free surface is simulated with CFD software. The range of wavemaking and wave height changes with depth and velocity. The appendages also cause wave.Wave and resistance caused by different appendages are computed. The hydrodynamicperformance of the Mini Underwater Vehicle sailing with attack angle and drift angle isdiscussed.3. Simulation of the Mini Underwater Vehicle conducted heaving, pitching, swaying and yawing is to calculate forces and moments caused by the motion in different depth.Hydrodynamics are computed by calculated results. Different hydrodynamic coefficient hasrespective changing rules versus depth. Dynamic pressure, velocity and wave making of theflow field are shown in this paper. Velocity, depth and motion frequency all make the flowfield different.4. Maneuverability experiment of the Mini Underwater Vehicle in different depth has beendone with planar motion mechanism. The resistance, vertical force and trim moment versusvelocity are measured by six-component balance in different depth. The lateral force and yawmoment of the Mini Underwater Vehicle sailing in drift angle is scaled in different depth.Also the Mini Underwater Vehicle is conducted heaving and pitching to calculatehydrodynamic coefficients of vertical plane in different depth.5. Motion features of the Mini Underwater Vehicle change near free surface because ofdifferent hydrodynamic coefficients. The maximum velocity diminishes near free surface.Trim angle and vertical velocity are different by dropping rudder and elevating rudder. TheMini Underwater Vehicle will submerge when sailing near free surface. Response to ruddertakes more time and the restoration moment shrinks.