Nonlinear dynamics of autonomous underwater vehicles in ocean currents

Ocean is human’s last frontier on Earth with most of its space inaccessible to human and remains
largely unexplored. For the protection of our ocean and its sound development, unmanned autonomous
underwater vehicle AUV, plays an increasingly important role. However, today’s AUV can’t function in a
strong current environment. Propeller-driven AUVs typically move at speeds of up to 1.5-2.0 m/s, and
thus strong ocean currents could push AUVs way from the planned paths. And their control surfaces
may not work properly, especially when AUVs are maneuvering. Extra thrusters may be added to
improve the maneuverability, yet the endurances of the vehicles will be shortened since extra thrusters
consume more power. On the other hand, buoyancy-driven underwater gliders, using internal actuators,
are characterized by long endurance. However, gliders typically move at horizontal speeds of about 0.3
m/s, which make gliders unsuitable for the missions in strong ocean currents. In the present research, a
hybrid AUV design will be studied which combines the capabilities of both AUVs and underwater
gliders. The proposed AUV will be propeller-driven yet the maneuverability of the vehicle in both
horizontal and vertical planes will be achieved by using internal actuators instead of control surfaces
and extra thrusters. The research will mainly focus on the control strategy of an AUV in a horizontal
plane by using internal actuators to exploit the vehicle’s coupling effect of the roll motion on horizontal
motions to maneuver AUV in a strong current environment.