Longitudinal Motion Control Of Supercavitating Vehicle

The speed of underwater vehicle is generally low due to the high viscous friction they received while moving.By utilizing super-cavitation resistance reduction technology,most of the body surface of the vehicle are wrapped in the vacuoles,which cut off the contact with the liquid environment from the vehicle,greatly reduce the sailing resistance and eventually realize underwater vehicle moving in a high-speed.Because of this advantage,supercavitating vehicle received a large amount of attention paid by researchers.In this paper,through both domestic and international literature review,an in-depth investigation on supercavitation model and related theory was performed.With the focused on the particular dynamics of ultra-cavitation state moving vehicle,detailed analysis towards the various parts of the vehicle affected by the forces of navigation was made and at last the mathematical model for the vehicle was established.Successively,the author applied sliding mode variable structure control and fuzzy sliding mode control strategies to achieve vehicle vertical navigation control as well as to perform simulation verification.The difficulty towards the investigation of the control methods of supercavitating vehicle lies on the accurate establishing of mathematical models.The forces received by the vehicle becomes quite complicated,given the fact that the vehicle is surrounded by vacuoles while moving.Especially the glide force in the tail of the vehicle,bring inconvenience to the realization of vehicle stable control.An in-depth investigation on the basic theory of supercavity and an analysis on supercavity form forecasting model were performed according to relevant literature review.On the basis of cavitation and rudder control configuration,a stress analysis towards vehicle cavitation,rudder and tail glide force was conducted.In the end,by getting six degree of freedom mathematical model,vehicle longitudinal motion of its simplified mathematical model got derived.Due to the existence of system parameter perturbation and external irregularity disturbance towards supercavitating vehicle model,based on the invariance of sliding mode control,through utilizing sliding mode control strategy to design vehicle longitudinal motion controller,establish method based law sliding mode variable structure controller.The simulation results show that the designed controller on the system variable parameters,external disturbances,such as uncertain status has strong robustness.However,there are also disadvantages towards sliding mode control method,after reaching the sliding motion of the system,state plane will produce high frequency chattering in its vicinity,so that the controlvolume and the amount of system state will produce high-frequency oscillations.Towards the chattering issue of sliding mode control,fuzzy control and sliding mode control are combined to create a new fuzzy sliding mode controller.Through simulation,fuzzy sliding mode control can suppress sliding mode control chattering generated,and can improve the dynamic quality of the system and ensure robust.