Ikuo Yamamoto Nagasaki R & D Center Mitsubishi Heavy Industries, Ltd. Nagasaki, Japan

　Hiroaki Hirayama Technology Research Center Japan National Oil Corporation Chiba, Japan

　Masami Matsuura Nagasaki R & D Center Mitsubishi Heavy Industries, Ltd. Nagasaki, Japan

　Norihiko Okamoto Technology Research Center Japan National Oil Corporation Chiba, Japan

　

A floating offshore platform is desirable for production of offshore oil fields. As the water depth of offshore oil fields increases, a position keeping control system on a platform equipped with thrusters has become essential. In the paper, a new dynamic positioning system (hereafter referred to as DPS) for offshore platform has been developed utilizing advanced control theory.

The authors also developed simulators named DP-TOP and DP-MAP. The DP-TOP can determine the thruster capacity, number, and location in advance by the Static analysis of DPS. The DP-MAP can simulate behavior of offshore platform motion quite matched with real system by the dynamic analysis including offshore platform and actuator models. The paper shows the flow chart of DPS design using these simulators.

Through a series of studies, the dynamic positioning system and its design method applicable to the real system were created, which are capable of obtaining a good positioning performance by a small thruster force under disturbed oceanographic and meteorological phenomena in petroleum developing areas.

　

Offshore oil development fields are now expanding to deep and severe environmental condition areas. For production of petroleum in deep areas, a floating production system is desirable. An example of a floating production system is shown in Figure 1. In order to maintain a high rate of operation of the entire production system, however, it is important to increase the rate of operation at the time of offshore shipping of oil from the floating production platform (FPSO) to a shuttle tanker. In order to increase the rate of operation at the time of offshore shipping, the relative motion between the FPSO and the shuttle tanker must be suppressed as small as possible, utilizing a DPS (Dynamic Positioning System) positively to raise a wave height limitation at the time of shipping of the oil. The DPS technology is indispensable for expanding the development into the deep sea area, therefore, intellectualized to increase the control performance and stability of the control performance and more assure the application of the technology to the actual machine.

For intellectualization of the DPS, the author and et al. have developed the feedback control system consisting of a thruster control force distributor by nonlinear programming theory and a control command generator by PID control and the feedforward control system by the application of fuzzy control^[1]-[3]. However, even these control systems could not solve the problems on the controllability of wave disturbance in the area ranging from the low frequency to high frequency areas.

In order to solve this problem, the dynamic positioning system for offshore platform has been newly developed utilizing advanced H∞ control theory^[4] (hereafter referred to as H∞control), and this paper describes that positioning system. The developed DPS consists of a control command generator by H∞control and a thruster control force distributor by nonlinear programming theory, and features that it can optimize (minimize)the robustness and thruster control energy of the system and generalize the application of the DPS to change thruster limiting conditions.

At the same time we have developed behavior analysis simulation tools, for a platform with a DPS, and established a technological assessment of that platform with DPS.

First of all, in the paper, We are going to explain the DPS control logic and thereafter go on to the behavior analysis simulation tools, named DP-TOP (Dynamic Positioning system -Thruster force Optimal distribution Program) and DP-MAP(Dynamic Positioning system - Motion Analysis Program). An investigation procedure of the DPS with this tools will be carried out. Finally we are going to conclude with the results of an efficiency inspection of the DPS control logic by real time control tests in a tank experiment.