Experimental study on trans-media hydrodynamics of a cylindrical hybrid unmanned aerial underwater vehicle

This paper presents the experimental investigation of the hybrid unmanned aerial underwater vehicle (HAUV) hydrodynamics during the water-air trans-media process. A novel experimental platform that can control the water-air transition profile of HAUV with different velocities, accelerations, and attitudes is firstly developed with the capability of measuring the precise hydrodynamic forces of the vehicle. This technique makes it possible to perform a series of constrained model experiments to obtain the hydrodynamic forces of HAUV during the water-air transition. The hydrodynamic forces on the HAUV changing with the velocity, acceleration, and attitude of the vehicle during the transition are measured. Analysis of the test data shows that when the velocity is more than 0.1 m/s, the suction force caused by the free surface effect increases first and then remains constant with the velocity increasing. The maximum value of the suction force is about 10% of gravity. At low accelerations, less than 0.15 m/s2, the vertical force is approximately proportional to the square of time. When the attitude is less than 15°, the hydrodynamic moment first decreases and then increases to a certain value. When the attitude increases, the hydrodynamic moment decreases directly to a certain value. The influence of the moment caused by hydrodynamic forces other than time-varying buoyancy cannot be ignored. These results contribute to the design, theoretical modeling, numerical simulation, and control of HAUV.