| Offshore oilfield wellhead platforms can meet the needs of human beings to develop new energy resources,which are of great significance to economic production.The wellhead platform jackets are immersed in water for a long time.A large number of marine organisms attached to the surface of the jacket have seriously affected the service life and service safety of the jacket.Therefore,the surfaces of the jacket need to be cleaned regularly.The current manual cleaning method has the problems of high risk coefficient,high cost and low cleaning efficiency.Therefore,this thesis develops a set of underwater operation robot for cleaning the jacket attachments of offshore oil field wellhead platforms instead of manual cleaning.Taking the underwater cleaning robot as the research object,the thrust allocation and fault-tolerant control of underwater robots are deeply studied.For the functional requirements of jacket cleaning,the structure of underwater cleaning robot is designed innovatively.According to the structure characteristics of the underwater cleaning robot,the Newton-Euler method is used to construct the dynamic model.And the hydrodynamic coefficients are quickly calculated by using the modified empirical formula.The correctness of the hydrodynamic coefficient and dynamic model are verified by CFD technology and dynamic simulation respectively.To solve the problem of thrust allocation of over-driven underwater vehicles,a mathematical model of the propulsion system of the underwater cleaning robot is established according to the spatial arrangement of the thrusters.In order to avoid thrust saturation,two thrust allocation two-step optimization algorithms are proposed based on the traditional pseudo-inverse method:pseudo-inverse interior point method and pseudo-inverse improved harmony search algorithm.Numerical simulation experiments are carried out to compare the effects of the two thrust allocation algorithms.The effectiveness of the algorithms is verified.To ensure the successful execution of the underwater robot under the condition of propeller failure,a dynamic surface controller is designed and a dynamic surface fault-tolerant control method based on thrust allocation is proposed.For the uncertainty of dynamic model error and ocean current interference,the nonlinear disturbance observer is used to estimate the disturbance and model error,and the stability of the controller is proved by the Lyapunov stability theory.The thrust allocation two-step optimization algorithm is improved,which improves the fault tolerance of the underwater robot.Finally,an experimental prototype of the underwater cleaning robot is developed.A series of experiments are carried out,including maneuverability experiment and oil well platform jacket cleaning experiment,in order to verify the functionality of the designed underwater cleaning robot. |
