A Study on the Optimization of Ship Maneuvering by Optimal Control Theory (2nd Report)

Abstract

In the previous reports"), the method for solving nonlinear optimal control problems of ship maneuvering motions is discussed and the optimal solutions for operating the control devices, such as rudder, CPP and side thruster, are given by them. In this paper, the above method is applied to obtain optimal control references for the feedback control systems. As the closed loop system is driven by the control references, the control reference is regarded as a control input for the closed loop dynamics. Therefore the optimizing technique presented in the provious reports can be applicable. Usually the control references are given by the step function. By using optimal control references instead of the step function, the motion controlled by the feedback system is improved. As the presented method overrides the previous controller, we call it OCS (Override Control System). Using a small training ship, some numerical simulations are carried out. Then some applications of OCS are shown for the dynamic positioning system controlled by the linear quadratic regulator (LQR). According to the results, the LQR can not be applicable for the nonlinear motion. However, by using the OCS it can be applicable even in the nonlinear region.