Rudder Roll Stabilization and Energy Minimization Using Factorized Nonlinear Generalized Minimum Variance Control for Underactuated Ships.

The plan of rudder roll stabilization controllers for underactuated vessels is complicated by model coupling, non-minimum phase dynamics in rudder to roll response and the limitation of rudder angle. A factorized form of the Nonlinear Generalized Minimum Variance (NGMV) control is applied for a rudder roll damping system. For the basic NGMV controller, the non-minimum phase subsystem is unstable when control costing approaches to zero. The factorization method can be used on this problem and provides a unique relatively simple controller. Since, the NGMV and FNGMV controllers require square system, the underactuated ship control system is simplified to a single-input-single-output (SISO) system, firstly. Then, the FNGMV based roll damping controller is presented and an energy consumption index (ECI) is proposed to evaluate the fuel efficiency of ship motion. Finally, simulations are shown to illustrate the validity of the roll stabilization control scheme and the effect of weightings on the energy measure.