| X-rudder underwater vehicles adopt new rudder arrangement and have better maneuverability,safety and hydrodynamics.There are x-rudder underwater vehicles originally designed for customer use in both oversea marine engineering equipment market and research project of some navy.Therefore,x-rudder will become more and more popular in rudder arrangement of underwater vehicles.However,x-rudder has not been adopted in domestic underwater vehicles yet.In order to conform with the development trends,it is significant to promote the application of x-rudder in domestic vehicles.Though many researchers have verified the advantages by simulations and developed some control methods,the achievement is limited.This thesis will continue with these work and focus on maneuverability,noise reduction and stealth,for the purpose of providing theoretical guidance and technical support.The space motion equation of the x-rudder underwater vehicle is the foundation for analyzing its maneuvering characteristics and designing motion controllers.To this end,the thesis analyzes the hydrodynamic characteristics of the control surace and its effect on the vehicles,and then combines the principle of superposition to derive the space motion equation applicable to the X rudder.According to this,two methods of torque attainable set and maneuverability simulation test are used to discuss its maneuvering characteristics.Aiming at the difficulty of manual operation,a cascaded control scheme is proposed which consists of robust adaptive dynamics controller,optimal control allocator and actuator characteristc compensator.In robust adaptive dynamics controller,projection operator is utilized to smooth the adaptation law and limit its amplitude,state estimator is designed to deal with external disturbance.In optimal control allocator,multi-objective constrainted minimization is adopted,then the deflection constraint,rate limitation and safety constraint can be addressed.The actuator characteristc compensator is developed by using Lyapunov’s theory and synchronization of actuators with vary dynamic performance is guaranteed.In order to solve the problem of requiring the vehicles to have fault diagnosis and fault-tolerant control capabilities for improving survivability,the unscented particle filter is designed in order to realize the autonomous diagnosis of control surface faults.A fault-tolerant control method based on control law reconfiguration is developed,assuming that the state of the fault rudder is known.Another fault-tolerant control method based on fault compensation is designed for the situation that the state of the fault rudder is unknown.The designed unscented particle filter can realize the online estimation of the actual state of the rudder surface by augmenting the deviation of the rudder effect as a state variable and without the Gaussian distribution assumption,which can provide the necessary information for fault diagnosis.The designed fault-tolerant control method can ensure that the vehicle still has a certain maneuverability when it encounters typical failures such as loose rudder,centering,damage and jamming,so as to improve the underwater survivability.In addition,this thesis also establishes the evaluation method of the maneuverability after the failure,which can provide data support for the behavior decision after the failure.In order to improve stealth by steering behavior optimization,the method of extending control period and minimizing control input is proposed,but it makes the controller design method for continuous system unapplicable.Therefore,model predictive control is introduced in low frequency autopilot and the optimal control input can be determined by predicting system states after a specified period of time and calculating the corresponding evaluation function.In order to judge whether the set steering period is reasonable,the discrete system analysis method is utilized to study the relationship between steering period and system stability,which provides a theoretical basis.In order to verify the effectiveness of the control method,this paper first carried out nemerous simulation tests,and the simulation results show that the proposed method is effective and feasible.Secondly,relying on the "new rudder steering test platform" project,an x-rudder underwater vehicle with rotatable stern rudders was developed,and physical verification tests were carried out in the towing tank and the maneuverability tank.The test results show that: 1)The x-rudder has better maneuverability than the cross rudder;2)The control method can control the movement of the vehicle by manipulating the x-rudder;3)The fault-tolerant control method is effective when single rudder or double rudder fails,but with applicable boundaries;4)The low-frequency steering method can extend the steering cycle within a certain range and ensure the control accuracy.These research results can not only promote the popularization and application of x-rudder,but also can be transplanted to other mobile robots with redundant actuators,which has certain application value. |
