Vibration Control of A Flexible Marine Riser System Subject to Input Dead Zone and Extraneous Disturbances

An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances. The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision. Specifically, based on the adaptive backstepping framework, virtual control laws and Lyapunov functions are designed for each subsystem. Three direction interference observers are designed to track the timevarying boundary disturbance. On this basis, the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone. In addition, the stability of the closed-loop system is proven by Lyapunov stability theory. All the system states are bounded, and the vibration offset of the riser converges to a small area of the initial position. Finally, four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller.