Boundary Control Of Flexible Marine Riser Systems With Output Constraints

As a tubular structure connecting offshore oil drilling platforms and seafloor,flexible marine riser plays an important role in offshore petroleum gas exploitation.However,due to the small stiffness of the flexible material itself,the influence of ocean currents,benthic organisms and other uncertainties in the marine environment,the flexible marine riser system is prone to vibration.Vibration of the riser may cause fatigue damage,which not only affects the working efficiency of the drilling platform,but also causes damage to the equipment,and may even lead to the leakage of petroleum gas,pollution of the environment,economic losses and ecological environment damage.Therefore,the study on vibration suppression of flexible marine riser system is of great practical significance to enhance the efficiency and safety of offshore petroleum gas exploitation.The purpose of this paper is to study the vibration control of a flexible marine riser system.Considering output constraints,saturated input constraints and unknown environmental disturbances,how to design a corresponding boundary controller to suppress the system vibration is discussed.The main contents of this paper are as follows:1)The boundary control of a flexible marine riser system with output constraints is studied.The flexible marine riser system is constructed as an Euler-Bernoulli beam by using Hamilton’s principle.Considering the influence of environmental disturbance,a boundary controller is designed,which uses the barrier Lyapunov function to ensure that the boundary slope of the flexible marine riser system is suppressed while the vibration is suppressed under the constraints.Then,the stability of the system is proved by the Lyapunov method.Finally,the validity of the controller is verified through numerical simulations.2)Vibration suppression of flexible marine riser systems with input saturation and output constraints is analyzed.Using barrier Lyapunov and saturated input,a boundary controller with an auxiliary system is presented.The controller not only suppresses the system vibration with input saturation,but also ensures that the system boundary satisfies the output constraint.Furthermore,the stability of the system is proved by the Lyapunov method.Finally,the effectiveness of the boundary controller is verified by simulation.3)The boundary control of flexible marine riser system based on adaptive neural network is studied.Considering unknown non-linear disturbances in the real ocean,the instability of the flexible marine riser system will be caused.Using radial basis function neural network to approximate unknown environmental disturbance,an adaptive neural network boundary controller is designed to solve the effects of bounded distributed disturbance and unknown boundary disturbance,satisfy the restrictions of system output constraints,and suppress the vibration of the riser as much as possible.Secondly,the Lyapunov method is used to prove the uniform boundedness of the closed-loop system.Finally,the effectiveness and advantages of the controller are verified by numerical simulation and comparison with the conventional proportional differentiation controller and existing literature controllers.