Task-space-based dynamic positioning for tandem loading operation between FPSO and shuttle tanker

Abstract

This thesis presents a cooperative weathervaning control strategy for the dynamic positioning of an FPSO and a connected shuttle tanker during a tandem loading operation. During the tandem loading operation, the relative motion between the two vessels may cause various hazards such as collision and hose disconnection. Weathervaning control enables both vessels to be oriented toward the direction of the mean forces induced by the ocean currents, wind, and waves so as to reduce the thruster power consumption and improve the operational safety. This study proposes a controller design in the task space that allows for weathervaning control without explicit measurements and/or estimation of ocean disturbance parameters (e.g., wind speed/direction, current speed). The cooperative control scheme is implemented in the controller of the FPSO to ensure the safety of both vessels as well as continuous oil transfer. A 3 degrees of freedom (DOF) dynamic equation of motion for a marine vessel assisted dynamic positioning system is represented in a state-space form, and environmental forces and moments acting on the marine vessel are numerically modeled using semi-analytical/empirical methods. Then, the relation between the task space and the configuration space is explained, and the task space of each vessel is defined. A controller design approach to dynamic positioning and the cooperative control strategy are proposed with an introduction of safety criteria and characteristics of tandem loading conditions. To evaluate the effectiveness and validity of the proposed controller, numerical simulations are carried out with several case studies, and the obtained results are presented.