| Manned submarines are equipped with a number of ballast tanks distributed along the hull. When these tanks are filled with water, they contribute with the submarine mass allowing it to submerge. In case of emergency they can act as a safety mechanism to drive the vehicle to surface: air is blown into the ballast tanks from very high pressure bottles expelling the water out of the tanks. This way the submarine loses weight, its buoyancy is higher, and it can emerge quicker. To fill the tanks with water, a valve located on the top of the tanks is opened, air escapes outside, and water flows into the tanks. These processes are known, respectively, as blowing and venting of ballast tanks.;Our aim is to study these processes providing all the necessary mathematical tools for their analysis, simulation and control. As a second step, we explore the potential use of these processes as a complementary control mechanism that could improve the maneuverability of manned submarines in certain situations. Particularly, we address the improvement of safety and stability in emergency rising manoeuvres and the control of hovering manoeuvres. Accurate hovering, the action of statically keep a desired depth, is essential, for example, for the launch and recovery of Autonomous Underwater Vehicles (AUVs), a subject that has recently raised an extraordinary interest.;We first propose a mathematical model for the blowing and venting processes which is coupled with the usual 6 degree of freedom kinematic and dynamic equations of motion. A rigorous mathematical analysis of the resulting state law is carried out. The control problem is formulated as a Bolza-type optimal control problem. Existence of solution for this problem is proved and the numerical resolution using a gradient descent method is addressed. We then propose a feedback control scheme for the tracking of the optimal trajectories obtained as a solution of this optimal control problem. For the hovering control, we propose a control law consisting of a sliding mode controller acting on a previously input-output exactly linearized system.;The numerical simulations carried out show that, indeed, an appropriate control of these processes can help in a significant way to improve stability and safety during emergency manoeuvres as well as be an invaluable tool for the hovering control. |
