Research On Hydrodynamic Modeling And Motion Control For Remotely Operated Vehicle

As an indispensable marine equipment for ocean development and integrated marine management,Remotely Operated Vehicle(ROV)has wide application prospects in many fields,such as marine resources exploration and exploitation,marine environment monitoring,marine scientific research,etc.With the increasing complexity and diversification of the underwater operating mission,higher requirements are put forward for the motion control performance of ROV.Whether ROV can finish the underwater operating mission stably,quickly and accurately depends on two key factors:an accurate hydrodynamic model and an advanced motion control system.Therefore,this paper focuses on the modeling and motion control of ROV.The main contents of this paper are as follows:(1)The spacial motion modeling of ROV.According to the geometrical structure and motion characteristics of ROV under actual operating conditions,the dynamic model of ROV is established by the reasonable simplification and hypothesis,and the properties of the parameters of the dynamic model are analyzed.(2)Numerical computation of ROV hydrodynamic coefficients based on CFD method.The computational fluid dynamics(CFD)method is applied to calculate the damping force of ROV in different motion modes by using the RANS equations and SST k-? turbulence model based on sub-domains hybrid meshes.The second order polynomial function is used to analyze the relationship between damping force and velocity,and then the linear and second order damping coefficients of ROV are determined.Based on the above steady results,the added mass of ROV is calculated by using unsteady motion and dynamic mesh technology in Fluent software.This method ensures the accuracy of ROV dynamic model and reduces the cost and time of hydrodynamic modeling.(3)Study on thrust control allocation of ROV driving system based on the mixed optimization objective.The hydrodynamic performance of ducted propeller under the influence of ROY is studied numerically by using the RANS equations and SST k-? turbulence model based on Fluent software,and the thrust model and thrust constraint conditions of thruster are established.Then,according to the above research results and the mathematical model of driving system on the vertical plane,a thrust control allocation function based on the mixed optimization objective and its solution method based on the smoothing newton method are designed.Finally,the simulation experiments comparison of the thrust control allocation method based on the mixed optimization objective and pseudo-inverse method are carried out.The results show that the proposed method can satisfy the thrust constraint requirements and effectively utilize the thrust set within the constraint range.(4)Design of composite nonlinear feedback sliding mode motion controller for ROY.Considering the uncertainties and disturbances of the system model,the CNF-SM controller is established based on composite nonlinear feedback control(CNF)and sliding mode control(SM).For the problem of chattering in sliding mode control,the hyperbolic tangent function is used instead of the sign function to reduce the chattering.Finally,the simulation experiments comparison of the Backstepping controller,CNF controller and CNF-SM controller of the ROV roll and yaw motion systems are carried out.Simulation results show that the designed CNF-SM controller has small overshoot,better robustness,and good fault tolerance for the added mass.