  This paper describes the modeling of a custom-made underwater glider capable
of flexible maneuvers in constrained areas and proposes a control system. Due
to the lack of external actuators, underwater gliders can be greatly influenced
by environmental disturbance. In addition, the nonlinearity of the system
affects the motions during the transition between each flight segment. Here, a
data-driven parameter estimation experimental methodology is proposed to
identify the nonlinear dynamics model for our underwater glider using an
underwater motion capture system. Then, a nonlinear system controller is
designed based on Lyapunov function to overcome environmental disturbance,
potential modeling errors, and nonlinearity during flight state transitions.
The capability of lowering the impact of environmental disturbance is validated
in simulations. A hybrid control system applying PID controller to maintain
steady state flights and the proposed controller to switch between states is
also demonstrated by performing complex maneuvers in simulation. The proposed
control system can be applied to gliders for reliable navigation in dynamic
water areas such as fjords where the sea conditions may vary from calm to rough
seasonally.
