Research On Fuzzy Sliding Mode Control Of A Remotely Operated Underwater Vehicle

Underwater robot, as an effective underwater tool, is used more and more widely in fields of ocean exploitation and scientific investigation. In order to accomplish complex tasks and ensure navigation safety, the underwater robot must perform the required actions under control. Underwater robot is a typical system which is characterized by high coupling, nonlinear and randomness. Therefore, it's difficult to realize precise motion control for an underwater robot.The Remotely Operated Underwater Vehicle (ROV) discussed in this thesis is a complex structure system which consists of umbilical cable, robot main body and several thrusters. In this thesis, a three-dimensional hydrodynamic mathematic model of the ROV in calm water is proposed firstly. In the model, the governing equations of umbilical cable are derived from the balance of forces at a point of the cable, these equations are taken as the core part for robot's hydrodynamic model, the whole model can then be established by introducing the boundary conditions of the cable equations at the conjunction point between lower end of cable and robot main body. Besides, a hydrodynamic mathematic model of the ROV in ocean current is proposed, which is based on the model in calm water and considers ocean current.Secondly, the Sliding Mode Control (SMC), which has a good robustness, is applied to design the trajectory and attitude controller on the basis of the hydrodynamic model proposed above. A decentralized sliding mode control strategy is used to realize decoupling control for the six-degree-of-freedom system. Meanwhile, an online Fuzzy controller, which is used to adjust certain parameters in SMC strategies, is designed to weaken chattering phenomenon of traditional SMC.Thirdly, a physical model of the ROV for Hydrodynamic calculation is built and a numerical method to solve hydrodynamic mathematic model of the ROV under certain control plan is proposed, using a mixed programming method based on Fluent software, Fortran and MATLAB languages.Finally, simulation experiments of the ROV in turning motion are carried out using the developed motion simulation platform. The simulation results show that the mathematic model built in this thesis can relatively truly reflect the hydrodynamic responses of the ROV under certain sea states, the fuzzy sliding mode controller performs well in motion control, the numerical calculation method is effective for the ROV motion simulation.