Research On Dynamics Analysis And Motion Control Of Multi-joint Underwater Vehicle

In the application of marine environment,multi-joint underwater vehicles are a class of elongated AUVs with multiple joints.The vehicle is equipped with propulsion and sideshift thrusters,which can change its shape and move flexibly through a narrower space or carry tools for operation.The vehicle has the characteristics of high redundancy,complex power control,and uncertainties such as external interference in underwater movement,it is impossible to establish an accurate dynamic model.In the face of complex paths,stable and controllable path tracking movements are the key to achieving accurate navigation of multi-joint underwater vehicles in restricted environments.In view of these problems,the following research is carried out.Firstly,a orthogonal gear drive structure and thruster layout of the multi-joint underwater vehicle are designed and appropriate types of driving motors and thrusters are selected.At the same time,the wall thickness design and stability and static pressure analysis of the pressure-resistant shell were carried out,and the specific composition of the control system and the overall structure of the robot were clarified.Secondly,establishing an effective dynamic model can improve the effect of motion control.Newton Euler method is used to establish the kinematics and dynamics equations of the multi-joint underwater vehicle,and the particularity of the different mass and length of each link of the robot is considered.Combined with Morrison equation,the interaction between rigid bodies and the thrust of thrusters,a more accurate dynamic model is obtained.And the accuracy of the dynamic equation is proved by combining the PD control law based on model compensation in Simulink.Thirdly,in order to obtain more accurate water resistance coefficient,the hydrodynamic simulation analysis of the multi joint underwater vehicle is carried out based on FLUENT.Taking the international standard submarine model as an example,the accuracy of the FLUENT solution method is verified,and then the water resistance simulation calculation of the robot under steady direct navigation motion was carried out.The water resistance formula and the friction resistance coefficient in direct direction are obtained by calculating the water resistance of the vehicle,which provides a more accurate hydrodynamic model for motion control.Finally,the path tracking method of multi-joint underwater vehicle is studied.According to the force distribution matrix of the thruster,combined with the linear path tracking scheme of integrating LOS guidance law,by two algorithms of fuzzy PID control and RBF sliding mode control,the controller is built on the Simulink simulation platform,and the path tracking simulation results are obtained,which verify the feasibility of the linear path tracking scheme.The tracking effects of the two algorithms are compared and analyzed,and more suitable control methods can be selected according to needs.