Analysis Of Hydrodynamic Performance And Motion Control Method Of Autonomous Underwater Vehicles

In order to ensure the normal use of oil pipeline underwater,it's necessary to inspect them regularly for the development and transportation of oil.The traditional inspection method is manual inspection and there are many disadvantages such as high cost,poor security,low efficiency,small range and so on.In recent years,with the rapid development of underwater robots.The problems mentioned above are solved well.However,remote operated vehicle are used more.Due to the presence of cables,the flexibility and the range of movement of robots are limited.Besides,the presence of cables is also a kind of hidden danger for underwater robots.The objective in this subject is a small and flexible unmanned underwater vehicle,and it has a certain degree of self-control ability.The purpose of its design is to inspect oil pipeline underwater.Not only the problems of manual inspection such as low efficiency and poor security,but the disadvantages of remote operated vehicle can be solved.The purpose of this thesis is to study mathematical modeling,force analysis,fluid analysis,motion simulation and motion control system of the autonomous underwater vehicle.As we all known,mathematical modeling is an important bridge to transform practical problems into mathematical problems.So,kinematical and kinetic equations are established after the prototype being made.Force analysis of the robot is made according to its actual working status,Finally motion models of each degree of freedom are established.Considering the motion underwater has great characteristics of non-linearity and coupling,it is difficult to establish precise motion model.Method of Computational Fluid Dynamics is used to make motion simulation and hydrodynamic analysis of underwater robot.Relationship between velocity and resistance is calculated and other related hydrodynamic coefficients are obtained by the simulation so that the motion model can be improved.On the basis of work ahead,motion control system of underwater robot is studied in this project.By comparing classical PID control algorithm and adaptive fuzzy PID control algorithm,It is concluded that the latter has better control performance.Based on this,depth controller and attitude controller are designed so that robot can cruise steadily at a certain depth under the water.In order to verify the validity of controllers,simulation by Matlab and a large number of pool experiments are carried out in this project.By collecting sensors data,the performance of controllers are analyzed and optimized at the same time.