Research On Dynamic Modeling And Robust Control Of Supercavitating Vehicle During Attitude Maneuver

Drag for motional body in the water is about 1000 times larger than that in the air,and skin friction drag is a main factor that limits the speed of underwater vehicles. Drag reduction of up to 95% can be achieved by using supercavitation technology, which is researched widely by all the world recently. However, due to special characteristics of supercavitation, supercavitating vehicles are quite different from traditional underwater vehicles. The location of the center of the pressure is forwarded, and added mass and damping torque are reduced, which make vehicle more sensitive to the response of external disturbances. Therefore, supercavitating vehicles pose technical challenges in system stability, maneuvering and control. Under this background, mathematics modeling and robust control problems are deeply studies on theory in the dissertation for supercavitating vehicle during attitude maneuver, which is funded by National Natural Science Foundation of China—"Studies on Mathematics Modeling and Control of Supercavitating Vehicle"(10802026) and the Research Fund for the Doctoral Program of Higher Education of China Item—"Studies on Stability and Control Strategy of Supercavitating Vehicle"(20080213003). The main contents of this dissertation are as follows:The stress analyses are completed in detail for supercavitating vehicle by using torpedo dynamics principle, and a nonlinear dynamic model of supercavitating vehicle is established. It offers theory foundation for analysizing the dynamic characteristic and designing control system.Based on the characters of supercavitating vehicle in the vertical plane, a simplified model of supercavitating vehicle in the vertical plane is derived. According to the results of analyzing the dynamic characteristic, an optimal controller is designed for supercavitating vehicle by using dynamic inversion theory. Simulation results show that control of supercavitating vehicle based on precise model during attitude maneuver can be solved by using dynamic inversion theory, and the LQR controller has robustness to a certain degree.There are many uncertainties such as modeling error of the vehicle object, system parameters uncertainties and so on, and the unknown disturbance on its tail. When the above uncertainties meet the matching conditions, a robust control scheme based on variable structure theory is proposed. A new sliding mode function is designed by using Backstepping theory. Based on adaptive estimation and variable structure theory, a strongly robust controller is proposed for supercavitating vehicle with the perturbation of cavity shape and cavitation number. The exponentially stable design method is proposed via Lyapunov method for fast time-varying uncertainties; moreover, the developed controller is proposed which doesn't have to know the upper bound of itself. The developed controller is achieved through adaptive variable structure control without the limitation of knowing the bounds of the uncertainties and perturbations in advance; Finally, the feasibility of the controller without memory effect is researched. Simulation results show that the planing force model without memory effect can be used in weak maneuvering vehicle.The guaranteed cost sliding mode function for a class of nonlinear system with mismatched uncertainties is designed via Lyapunov method, and sufficient condition for the existence is given. The design process of the exponentially stable variable structure controller and the correspondent adaptive variable structure controller is presented, and the controllers are applied into attitude controlling of supercavitating vehicle. According to common mismatched uncertainties, the attitude tracking controller of supercavitating vehicle based on Backstepping method. Simulation results show that the two above controllers can guarantee the robust performance of underwater vehicle.