Design And Key Technologies For Quadrotor Unmanned Underwater Vehicle

The ocean is the treasure that human beings have not fully explored.It is also an important strategic goal to ensure China's sustainable development.Due to limitations of the human body,the development of marine engineering equipment represented by unmanned underwater vehicles has become a significant route to explore,develop and utilize the ocean.With the growing demand for construction of the ocean,various ocean operation tasks have become more and more complex,which increases the diverse requirements for unmanned underwater vehicles.Based on the analysis of existing unmanned underwater vehicles,this thesis proposes a new quadrotor underwater vehicle with thrusters configured as X shape.Key technologies of the new quadrotor underwater vehicle have been systematically analyzed and studied in the thesis.The key technologies contains system design,mathematical modeling,motion control and formation control.Relevant theoretical results are verified by simulation and pool experiments.The main research contents of this thesis are summarized as follows:1)The four thrusters of the quadrotor underwater vehicle are proposed in the form of X shape,and motion mechanism of the underwater vehicle with this thrusters arrangement is analyzed.The X shape arrangement of the thrusters makes space motion of quadrotor underwater vehicle into four kind of independent motion,namely surge,heave,roll and pitch-yaw,which makes it show better motion performance.2)According to modular principle,quadrotor underwater vehicle system made up of mechan-ical system,central control system,communication system and power system are analyzed and designed.For the mechanical system,the overall shape of the underwater vehicle adopts near-ly streamlined shape without considering the thrusters,and it is divided into 5 sections.For the central control system,the digital signal processor(DSP),the Advanced RISC Machine(ARM)and the Attitude and Heading Reference System(AHRS)are selected to work together to ensure autonomous control of the underwater vehicle.For the communication system,electromagnetic waves or acoustic waves communication are used for wireless communication according to envi-ronment,and a frame-based data transmission protocol is designed to ensure transmission accura-cy.For the power system,the thrusters and battery are selected based on the resistance estimation results of surge and heave motion.3)For the quadrotor underwater vehicle,a black box modeling method based on particle swarm optimization and support vector machine is proposed.Firstly,according to the general form of the underwater vehicle model,the input and output of the black box model are obtained by discretization processing.Then,the support vector machine is used to construct the nonlinear mapping relationship between input and output.And after that the particle swarm optimization algorithm is used to obtain the best set of parameters for support vector machine.Finally,the black box model of the quadrotor underwater vehicle can be obtained.The experimental results of space motion show that the proposed method can effectively predict the motion state of underwater vehicles.The black model is almost consistent with the actual model,which is helpful for the initial analysis and design of the underwater vehicles.4)For the quadrotor underwater vehicle,the specific form of the mathematical model consid-ering its own characteristics is analyzed and established.Based on the general form of underwater vehicle model,the mathematical model of the quadrotor underwater vehicle with its own character-istics is established by analyzing the hydrodynamics and control force from quadrotor underwater vehicle prototype.According to hydrodynamic analysis,the quadrotor underwater vehicle can be roughly divided into two light-coupled subsystems:(u,q,r)and(v,w,p,),which conforms to the independent surge and heave motion.5)For the quadrotor underwater vehicle,a sliding mode motion controller with strong robust-ness is proposed.The quadrotor underwater vehicle is a typical coupled nonlinear system with uncertain model parameters and external disturbances.Therefore,this paper adopts a sliding mode control method based on the approach law to design controllers with robustness for forward(surge)motion,vertical(heave)motion and space motion of the quadrotor underwater vehicle.When de-signing the space motion controller,the objective function is adopted as minimizing the roll and pitch moment generated by the thruster,and then lagrange optimization method is applied to make the multiple solutions of the original four thrusters into one set of unique solutions.Simulation of forward motion and vertical motion shows the feasibility of the X shape for thruster layout.Simulation and pool experiment of space motion show that the sliding mode controller proposed in this paper effectively copes with the uncertainty and can fully guarantee autonomous motion of the quadrotor underwater vehicle.6)For the quadrotor underwater vehicle,a three-dimensional formation control scheme is pro-posed by combining backstepping technique,leader-follower strategy and sliding mode control.It has strong robustness in three-dimensional space and only need to transmit position informa-tion.Underwater acoustic communication is relative slow.It is necessary to consider reducing the amount of information transmitted between the quadrotor underwater vehicle when design-ing formation control.The formation control scheme proposed in this paper consists of a global leader controller and a follower controller.For the global leader controller,a trajectory tracking control law with certain robustness in three-dimensional space is designed based on backstepping technique and sliding mode method.For the follower controller,a virtual trajectory is introduced,which is only related to the actual position of the leader and the expected relative position of the follower.Let the virtual trajectory converge to the follower's desired trajectory,and then control law is designed for the follower to ensure actual trajectory of the follower converge to the virtual trajectory.Together with the global leader controller and the follower controller,all underwater vehicles move in the desired formation.Simulation results of triangular prism formation com-posed of six quadrotor underwater vehicles prove the correctness and effectiveness of the proposed formation control scheme.