Robust control methodology applied to the design of a combined steering/stabiliser system for warships

The consequences of roll motions in ship operations can seriously degrade the performance of mechanical and personnel effectiveness. To alleviate roll motions many ships are equipped with fin stabilisers. Rudders can also generate roll motions which can be harnessed to function in congress with the fins to accrue enhanced levels of stabilisation. An integrated rudder and fin stabilisation control strategy is proposed. Rudder roll controllers and autopilots are developed using the H^∞ optimisation technique and their performance compared with the classical counterparts. Simulation studies are described that quantify the performance of the various controllers. The level of interaction present between the yaw and roll control loops is also examined. The study concludes that the overall performance of the H^∞ controller and autopilot is superior to that of the classical type. The level of interaction between the two loops can be suitably modified by varying the performance weighting functions. The study has concentrated on designing the controllers for frigates of the Royal Navy, however, the approach is suitable to present and future warship design