ABSTRACT:

The paper is concerned with a reentry control problem of moving a riser pipe hanged off and positioning its lower end just above a target. The difficulty of the manual control motivates us to design an automatic control system for dynamic reentry in current. A motion equation of a riser pipe model in current is derived via modal analysis. Then LQI (Linear Quadratic with Integral action) control methodology is applied to obtain an appropriate reentry controller. Experimental successful results on reentry control are shown.

INTRODUCTION

In Sept. 2007, the deep sea drilling vessel „Chikyu‟ began drilling operations in the Kumano Basin area of the Nankai Trough for the start of IODP (Integrated Ocean Drilling Program). As introduced in Curewitz, Kuramoto, Kawamura (2006), the vessel is a state-of-the-art drilling platform that can reach geological targets previously inaccessible to scientific drilling. This is equipped with a drilling derrick, a fully integrated riser drilling system, and a highly automated drill floor system that runs efficiently and safely with a small number of operating personnel. As for the important technologies in order to make a long expedition possible by „Chikyu‟, Takagawa (2002) pointed out DPS (Dynamic Positioning System), AHC (Active Heave Compensator) and flee-away capabilities. Then it must be conducted such that the crush between LMRP and BOP is avoided. In general, in such a reentry operation, it is required for a drill operator to incorporate ROV (Remotely Operated Vehicle) operations for observing the bottom of a riser pipe into DPS operations for a mother vessel. The reentry operations in current anytime result in time-absorbing works because of the difficulty of estimating the behaviour of a flexible and long riser even if the distance between LMRP and BOP is measured with accuracy.

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