  Unmanned aerial vehicles (UAVs) are finding their way into offshore
applications. In this work, we postulate an original system that entails a
marine locomotive quadrotor UAV that manipulates the velocity of a floating
buoy by means of a cable. By leveraging the advantages of UAVs relative to high
speed, maneuverability, ease of deployment, and wide field of vision, the
proposed UAV$-$buoy system paves the way in front of a variety of novel
applications. The dynamic model that couples the buoy, UAV, cable, and water
environment is presented using the Euler-Lagrange method. A stable control
system design is proposed to manipulate the forward-surge speed of the buoy
under two constraints: maintaining the cable in a taut state, and keeping the
buoy in contact with the water surface. Polar coordinates are used in the
controller design process to attain correlated effects on the tracking
performance, whereby each control channel independently affects one control
parameter. This results in improved performance over traditional
Cartesian-based velocity controllers, as demonstrated via numerical simulations
in wave-free and wavy seas.
