ABSTRACT: The authors developed the 3 Dimensional Dynamic Positioning Systems (hereafter referred to 3-D DPS) for offshore platform. The system consists of a thruster total force and moment distribution element, a command generation element, a thruster manipulation signal determination element for feedback control, and a fuzzy control for feedforward control.
INTRODUCTION DPS is important for offshore platform (Sørensen, A. J., 2001, Aalbers, A. B., 2001, Tannuri, E. A., 2001, Katebi, M. R., 2001) and minimum energy for position control were well described and shown by control simulation in Brink and Chung (Brink, A. N., 1981). The total force and moment distribution algorithm is created by 3 dimensional Nonlinear and linear programming to minimize the total energy evaluation function which is originally found, and a command generation produces the total force and moment command to keep at a position and reduce not only thrust, but also roll and pitch motions. The fuzzy control has function to reduce the environmental force such as current, wind and wave. The DPS is effective to keep a position of surge, sway and yaw motion at the minimum energy and has robustness against environmental disturbances. In addition to that, the DPS can control 3- D motion, such as surge, sway, heave, yaw, roll, and pitch by setting up actuators. For example, the DPS can control not only surge, sway, and yaw, which is conventional motions to be controlled, but also reduce roll motion by using such special actuator as disturbances Voith- Schneider propeller (VOITH, 2012). Also, the developed system can determine the yaw angle at the minimum roll and pitch angles against environmental disturbances, when a position keeping is needed for conventional offshore platform and thrusters. The effectiveness was confirmed by 256m length, 42m width semi-sub type offshore platform experimental data.