Reduction of Effect of Waves Disturbance on Ship Roll Motion by Using Robust Nonlinear H∞ Control

This paper presents a new robust fin control method based on L2 gain design to reduce ship roll motion and waves disturbance effects. The process involves the nonlinear dynamics of the ship roll and its fin actuator.  External disturbances of waves and model parameters variations are considered as process uncertainties. The state feedback controller is designed to reduce the effect of wave disturbance on the controllable variables of the process. For controller design, nonlinear H∞ approach has been employed in the sense that it ensures the stability of the process and achieves the desired control objectives. To solve the inequalities associated with the nonlinear H∞ problem, an efficient SOSTOOL-based algorithm is presented. Simulation results are presented to evaluate the efficiency of the proposed approach. In order to validate the proposed algorithm, it is compared with PID controller. Results show the superiority of the designed controller based on Robust Nonlinear H∞ control over PID controller.