Dynamic Ship Positioning Control Systems Design Including Nonlinear Thrusters and Dynamics

The control systems for dynamically positioned oil-rig drill ships, support vessels and survey vessels include filter to remove the wave motion signal. This is necessary because the thrust devices are not intended and are not rated to suppress the wave induced motions of the vessel. A combined self-tuning filter and Kalman filter scheme is proposed for this role and an optimal state estimate feedback control scheme is described. The ship dynamic equations are nonlinear and significant nonlinearities are present in the thrust devices. The self-tuning filter has the advantage of maintaining optimum performance in different weather conditions and of compensating for the modelling errors introduced by the nonlinearities.