An autonomous underwater vehicle as an underwater glider and its depth control

To provide a conventional autonomous underwater vehicle with gliding capability, we assume a moving battery and a buoyancy bag installed in a torpedo shaped autonomous underwater vehicle. We develop a mathematical model for the underwater vehicle and derive a stable gliding condition for it. Then an LQR controller is designed to control the zigzag depth of the vehicle, where the derived gliding condition is used as set-points of the control system. For control efforts in the gliding movement, the changes in the center of gravity and the net buoyancy are used, but neither thruster nor rudders are used. By using the gliding capability, the underwater vehicle can move to a farther location silently with less energy consumption and then start operating as a normal autonomous underwater vehicle. We show the feasibility of the proposed method by simulations using Matlab/Simulink.