| Underwater travel is greatly limited by the speed that can be attained by the vehicles. Usually, the maximum speed achieved by underwater vehicles is about 40 m/s. Supercavitation can be viewed as a phenomenon that would help us to break the speed barrier in underwater vehicles. The idea is to make the vehicle surrounded by water vapor while it is traveling underwater. Thus, the vehicle actually travels in air and has very small skin friction drag. This allows it to attain high speeds underwater. Supercavitation is a phenomenon which is observed in water. As the relative velocity of water with respect to the vehicle increases, the pressure decreases and subsequently it evaporates to form water vapor. Supercavitation has its drawbacks. It is really hard to control and maneuver a supercavitating vehicle. The first part of this work deals with modeling of a supercavitating torpedo. Nonlinear equations of motion are derived in detail. The latter part of the work deals with finding inner-loop controllers to maneuver the torpedo. A controller is obtained by LQR synthesis for pitch and roll rate control. Robust controllers are obtained by mu/Hinfinity synthesis for tracking pitch and roll angle commands. The robustness analysis of the LQR controllers is carried out by calculating the gain and phase margins. Simulations of the response for a perturbed system also have been studied. The inner-loop controllers are used for guidance and navigation of the vehicle. It is observed that the pitch and roll angle controllers can be used for yaw rate control of the vehicle. This is applied to the homing guidance problem. A simplified case is solved for homing guidance. |
