Dynamics Analysis And Attitude-orbit Control For Incomplete-encapsulated Supercavitating Vehicles

At present,supercavity is applied to achieve a great drag reduction,which is an effective technology to improve the speed of underwater vehicles.It has been listed as one of the key projects in the planning of underwater high-speed weapons by various military powers.By adopting high performance propulsion technology,natural cavita-tion bubble or artificial aeration cavitation bubble can be formed and the navigation body can be wrapped by cavitation bubble,so as to reduce the navigation resistance.In particular,more and more attention has been paid to the special characteristics of the partially submerged supercavitating vehicles.However,the incomplete encap-sulation of bubble also brings considerable challenges to the control system of the vehicle.The dynamic characteristics of the vehicle are also complicated by the incom-plete inclusion of cavitation bubbles.Therefore,carrying out for the research of the Incomplete Encapsulated Supercavitating Vehicle(IESV)control system has impor-tant theoretical value and practical significance,since it is helpful to reveal the IESV navigation complex dynamic characteristics,to improve the supercavitating vehicle of motor performance,and to promote the engineering applications of supercavitation technology.This paper analyzes and models the dynamic characteristics of supercavitating vehicle in incomplete encapsulated states,and studies the attitude and orbit control of the vehicle.The main work and research results of this paper are as follows:(1)Analysis and modeling of dynamic characteristics of the incomplete encapsu-lated supercavitating vehicle.Taking the incomplete encapsulated supercavitating vehicle as the research object,our works start from the prediction model of cavity profile,and the force characteristics of the vehicle in this state are analyzed,and on this basis,the dynamic characteristics model of the incomplete encapsulated supercavitating vehicle is established.The dy-namic model is further processed to obtain a two-degree-of-freedom dynamic model in the longitudinal plane of the vehicle.Through the simulation experiment,the longi-tudinal dynamic characteristics and dynamic performance of the vehicle are analyzed,which lays the foundation for the further study of the control system.(2)Design of the IESV controller with uncertain of tail differential pressure com-putational efficiency.In view of the uncertainty of the efficiency of the tail pressure in the incomplete encapsulated supercavitating vehicle's force analysis,this efficiency parameter is con-sidered as a single unknown parameter in the system.Otherwise,the cavitator and the direct lateral force of the tail are designed as the control inputs.A backstepping variable structure controller is proposed and a parameter adaptive law is designed to estimate the uncertainty efficiency parameter.An extended state observer is de-signed to estimate and compensate the unknown external interference terms with norm bounded in the system model.Through theoretical proof and simulation analysis,the control effectiveness of this method for the existence of unknown single parameters in the system is verified.The effect of bubble length on the control performance is analyzed by simulation.(3)Design of the IESV controller with the model uncertainty.At first,for some elements of the IESV can t be measured,such as the length of the cavity package,the maximum area of the tail force,and the interference of air bubbles,which make the system has the problem of the model uncertainty.An attitude and orbit controller is proposed by taking advantage of the backstepping con-trol theory.The unknown elements mentioned above together with the state variables constitute multiple unknown items.The Radial Basis Function(RBF)neural network is used to approximate the unknowns in the model at the same time.An adaptive method based on the stability theory of Lyapunov is used to calculate the weights of neural networks,and the stability of the system is also proved.Second,a simplified case considering the model uncertainty is that although system parameters are known in many engineering applications,the accuracy cannot be guaranteed by empirical for-mula.For this situation,a Calculated Torque Controller(CTC)is proposed to solve the attitude and orbit control problem of the IESV.The model error is estimated by RBF neural networks when the model is known and the model error exists.Theo-retical proofs and simulation results verify the effectiveness of the proposed control algorithm.(4)Study on IESV control method considering actuator saturation characteristics.In view of the non-smoothness saturation of the actuator that may occur during maneuvering of the IESV,an anti-saturation controller design is developed.A contin-uously differentiable asymmetric saturation model is designed based on the Gaussian error function to solve the nonlinear problem of conventional non-smooth saturated actuators.An adaptive RBF neural networks controller is designed to estimate the unknowns in the system,and the attitude controller is designed by the backstepping method.Finally,based on the Lyapunov stability theory,it is proved that all the state variables in the closed-loop system are uniformly ultimately bounded,and the tracking error can converge to the neighborhood with a small zero value.Simulation results confirm the effectiveness of the proposed controller.