Model-Based Feedback Control of High-speed Supercavitating Vehicles

Supercavitation is a means of drag reduction in water, wherein a body is enveloped in a gas layer in order to reduce skin friction. Depending on the type of supercavitating vehicle under consideration, the overall drag coefficient can be an order of magnitude less than that of a fully-wetted vehicle. However, even in its simplest conceptualization, supercavitating vehicle dynamics features slope-discontinuous force curves and time-delay effects, control presents special challenges. This paper has presented strategies for the control of the highly-coupled nonlinear system comprising a supercavitating vehicle. A three DOFs hydrodynamical model based on Newton’s Laws was implemented for simulating the behavior of such a system. The linearization of the mathematical model is derived in detail. A Linear Quadratic Regulator (LQR) control design for the vehicle was formulated. Results of dynamical simulation for a specific vehicle were presented both for uncontrolled flight and with LQR-based feedforward-feedback control. The system behavior is dominated by the distinct change in the nature of the forces as the afterbody moves between a planing and non-planing condition, but that under the assumptions made for the three DOFs model the controller can eliminate the most undesirable behavior in either case.