In this paper, the development of a model scale Dynamic Positioning System(DPS) is described. The system is composed of a main computer, a monitoring computer, controller and thrusters. Positions are measured by using an optical position sensor system. Optimal control theory(LQI) is adopted for the design of the position controller. A series of position keeping experiments in both calm water and waves were performed for a moored floating body, which has the 3-dof motion of surge, sway and yaw. The controllability and applicability of the designed dynamic positioning system are verified through the model tests and the effects of low frequency motion filters are investigated.


As deep sea operations grow up, it is expected that the use of DPS increases. Furthermore, it is required that the DPS is capable of more sophisticated and complicated missions such as tracking operations for deep sea mining, cable laying and etc. Model test of a DPS can provide useful information for not only developing a complicated prototype DPS but also evaluating a designed DPS. Nakamura and Koterayama et a1.(1994, 1995) showed usefulness of simulation and model experiment of a thruster assisted mooring by using LQI control algorithm for sway motion. In this study, a model scale dynamic positioning system is developed by using LQI control algorithm. Four rotatable thrusters are employed for providing the thrust necessary fir sophisticated missions in demand. Thruster angle, however, is not controlled during the test. (X, Y) position and heading angle are taken as object function for position keeping control. Hardwares for the tests are composed of 3 computers, thruster modules, a set of photo-electronic position sensors, and very soft springs which prevent the model drifting away from the measurement area.

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