Nonlinear adaptive depth tracking and attitude control of an underwater towed vehicle

This paper addresses the problem of simultaneous depth tracking and precise attitude control of an underwater towed vehicle integrated in a two-stage towing arrangement. A nonlinear Lyapunov-based output feedback controller is designed to operate in the presence of plant parameter uncertainty and proven to regulate pitch, yaw, and depth tracking errors to zero. When subjected to bounded external disturbances, the tracking errors converge to a neighborhood of the origin that can be made arbitrarily small. In the implementation proposed, a nonlinear observer is used to estimate the linear velocities used by the controller. The results obtained with computer simulations including sea wave driven disturbances and sensor noise, show that the controlled system exhibits good performance about different operating conditions and holds considerable potential for oceanographic missions that require simultaneous depth and attitude control.