Research On Safe Navigation Control Method For Air Cushion Vehicle Under Uncertain Conditions

Air cushion vehicle(ACV),as a kind of high performance ship,breaks through the serious obstacle to the speed increase caused by the support mode of traditional displacement ship,and navigates on the surface in the form of cushioning,which has advantages of high-speed and amphibious.Therefore,the navigation of the ACV is not limited by the water depth,and can travel on the surface at high speed,for example,ice surface,swamp,beach,grassland and so on,which cannot be achieved by other displacement ships.This "special ability" enables the ACV to complete the tasks in many special environments.However,the ACV's special mechanism and the hull structure make the modeling of ACV very difficult,especially water-air resistance model caused by the discharge between flexible skirt with finger and navigation surface as well as air-cushion pressure of cushion system.Theoretical research and experiment show that the model parameters of ACV vary greatly with different states.In addition,it is influenced by marine environment disturbances during navigation.Therefore,the ACV exists the uncertainties consisted of parameter uncertainties,modeling error and other unknown disturbing influences.In addition,the hull resistance in cushion navigation is smaller than that of displacement ship.The phenomenon of stall,drift and roll occurs easily during turning and the navigation risk exists caused by the problem of resistance peak,high-speed tail-swinging and safety limit.Therefore,the research of safe navigation control method of ACV under uncertain conditions has great significance and engineering practical value.Focusing on the uncertain problem consisted of parameter uncertainties,modeling error and other unknown disturbing influences,and the navigation risk of resistance peak,high-speed tail-swinging and safety limit caused by self-navigation characteristics,the main research works of this paper are as follows:(1)Aiming at the problem of uncertain parameters in the complex water-air resistance of the ACV,a resistance approximation method via parameter adaptive identification is proposed.Based on this method,the adaptive compensator is obtained.The Lyapunov stability analysis method is used to design the speed and turn rate control laws and adaptive identification law of ACV,and the model parameter adaptive controller with the adaptive compensator is obtained.It is proved that the designed model parameter adaptive controller including the adaptive compensator can effectively suppress the influence of nonlinear resistance with parameter uncertainties,improve the control accuracy,and guarantee the ACV to complete the control tasks of speed and turn rate with high precision.(2)Aiming at the nonlinear characteristic of ACV's complicated dynamics and the effect of the uncertainties consisted of parameter uncertainties,modeling errors and other unknown disturbances,a double compensation full-order sliding mode control method is proposed for ACV based on finite time observer.According to the analysis of dynamics' uncertainty problem,the description method of uncertain dynamics' model which conforms to the design form of finite time observer is proposed.Then,a finite time observer is designed to observe the dynamics' uncertainty.The observation information of observer is used to construct the uncertain compensation part,and the approximate nonlinear model is used to construct the approximate compensation part,then the double compensation full-order sliding mode controller is designed.The simulation results demonstrate that the double compensation full-order sliding mode controller can effectively weaken the influence of nonlinear characteristic and uncertainty of ACV's complicated dynamics,and ensure the ACV to complete the control task with high precision.Compared with three different methods,the designed double compensation full-order sliding mode controller can contribute to higher tracking accuracy.(3)Aiming at the safety risks of stall,drift phenomenon and tail-swinging caused by the excessive turn rate,a state safe space of ACV is established and a navigation control method constrained by the space is proposed.According to the safety limits of drift angle and turn rate at different speed,the state safe space is proposed for ACV's safe navigation based on the neighborhood and the state space.Combining the auxiliary dynamic equation method,the finite time observer and the sliding mode method,the speed and course controllers constrained by the state safe space are designed for ACV.The simulation results demonstrate that the designed controllers can ensure that the state point composed of speed,turn rate and drift angle are always in the state security space during the course of tracking,thus ensuring the safety of navigation.(4)In the process of trajectory tracking control of ACV,the trajectory tracking controller without guidance link sometimes produces unreasonable output that threatens navigation safety.Aiming at this problem,a trajectory tracking control method with a safe self-adjusting guidance law is proposed for ACV.According to the position tracking error,the virtual velocity law is designed to guarantee the finite time convergence of the error.Based on the finite-time auxiliary dynamic equation,the guidance law which can automatically adjust the virtual velocity error to the safety error is designed,and the controller which can ensure the convergence of the safety error is designed.The simulation results demonstrate that the designed controller can ensure that the speed,turn rate and drift angle are in the safe range during the process of trajectory tracking control,and the control instructions assigned to the air ducted propeller and the air rudder by the controller are in their output capacity range.