Modeling and control allocation for ship berthing system design

In the harbor area, precise steering is the most important operation. This operation requires a set of adequate thrust devices with exactly taken into account surge, sway and yaw motions. However, at low speed maneuvering, the effectiveness of actuators is nominal, thus using assistance of tugboat is necessary to ensure safe berthing operation. In this paper, the mathematical model of system that describes the interaction between unactuated ship and tugboats is presented. Thrust allocation is solved by using the redistributed pseudo inverse (RPI) approach to determine the thrust and direction of each individual tugboat. The main goal of this approach is to minimize the power supplied to tugboats and increase their controllability under constraints that the tugboat can only exert a limited pushing force and can only change direction slowly. Additionally, the adaptive control law is proposed to capture the draft coefficients of ship which are known as uncertainty parameters. The controller guarantees the ship follows the path (geometric task) with desired velocities (dynamic task). Particulars of Cybership I which is a model ship are used to evaluate the efficiency of proposed method through Matlab simulation.