Nonlinear Modeling And Control Design Of A Supercavitating Vehicle

The supercavitation vehicle, which is realized by reducing 90% of the water drag with supercavitation technology, is a new generation high speed underwater weapon. The torpedo and projectile speeds could respectively reaches 100 m/s and 1000 m/s when the most or complete bodies’ surface is covered respectively by the ventilated or natural supercavities.There are significant differences between charateristics of traditional underwater vehicle and supercavitating vehicle, through the supercavitation vehicle have high speed. Most of surface of the vehicle surrounded by gas, which introduces abcence of buoyant force. It is a very hard challenge for the dynamics modeling and control. The nonlinear dynamics modeling and control of the supercavitation vehicle, which are intensive studied in this thesis. The specifice research content in this thesis is presented as follow:Base on the Principle of the Independent Expansion of the cross sections of the supercavity, cavity memory effect and its influence on cavity shape are investigated. The orientation effect of cavitator, cavity deformation by the buoyancy, the efficiency variation of the fins of the vehicle are analysed respectively. The hydrodynamic forces acting on different parts of the vehicle are incentive investigated and calculated. Finally, with these results, the nonlinear dynamic model of the supercavity vehicle is derived, which established the foundations of dynamics features analysis and control strategy design.The dynamics model of supercavitating vehicle is simplified to longitudinal dynamics model. The open loop simulation results of the dynamic model is performed with different initial conditions. The effects of the cavitator and fins on the motion stability of the vehicle are analysed. Planing force increased with the increase of the initial disturbance. The systems in different cavitation condition have similar dynamics response.To aim at the problems of depth tracking the roubust pole place controller based on the input-output exact linearization, which is designed here, has good performance. The shortcoming of this controller is likely to have problem of input saturation. For further research model prediction controller designed here for decrease the planing force. The simulation results indicate that the MPC controller could avoid the planing force successfully by constrains the distance of the vehicle tail and cavity wall, and the motion stability of the vehicle is consequently improved.In the stage of accelerated motion of supercavitating vehicle, the cavitation number is decrease with increase of speed. Dynamic characteristics is changes with the increase of cavity size. Robust controller is designed to aim at the perturbation of hydrodynamic force coefficient. Further, gain scheduling control strategy is designed for variational speed and cavitation number of the vehicle. Simulation indicate that the system could be stabilized in the presence of initial disturbance and uncertainty of cavitation number.