Design and Comparison of H∞/H2 Controllers for Frigate Rudder Roll Stabilization

Abstract

Roll motion of ships can be distinguished in two parts: an unavoidable part due to their natural movement while turning and an unwanted and avoidable part that is due to encounter with waves and rough seas in general. For the attenuation of the unwanted part of roll motion, ways have been developed such as addition of controllable fins and changes in shape. This paper investigates the effectiveness of augmenting the rudder used for rejecting part of the unwanted roll, while maintaining steering and course changing ability. For this purpose, a controller is designed, which acts through intentional superposition of fast, compared with course change, movements of rudder, in order to attenuate the high-frequency roll effects from encountering rough seas. The results obtained by simulation to exogenous disturbance support the conclusion that the roll stabilization for displacement can be effective at least when displacement hull vessels are considered. Moreover, robust stability and performance is verified for the proposed control scheme over the entire operating range of interest.