LEARNING TRACKING CONTROL OF OCEAN STRUCTURE UNDER UNKNOWN DISTURBANCES
Hideyuki Suzuki, Koichiro Yoshida and Qi Tao, Department of Naval Architecture and Ocean Engineering, University of Tokyo, Tokyo, Japan
ABSTRACT
When an ocean structure is constructed from several part-structures, the construction operations, such as mating, positioning and transportation of these structures at the construction site, must be carried out under various disturbances. This paper presents learning trajectory tracking control when a structure is transported repeatedly along the objective trajectory under unknown steady disturbance.
Corresponding to the premise, a learning controller which is constituted by both feedback controller and feedforward controller is proposed. The controller improves its feedforward control force every time it tracks the same objective trajectory by learning unknown disturbances from the difference between the objective trajectory and previously realized trajectory.
In this study, simulations and basin experiments, using a model of a semi-submersible are conducted. The learning controller showed good performance in both simulation and basin experiment under the unknown disturbances.
DIVERLESS FLOWLINE CONNECTION SYSTEM
David S. Cox, Sonsub International Pty Ltd, Welshpool, Western Australia, Australia
ABSTRACT
The tie-in of flowlines and umbilicals to subsea trees and manifolds in deep water has traditionally been an expensive exercise. It generally requires the simultaneous presence of lay vessel and drill ship, or divers using a combination of rigging and gantries on the subsea structure. In recent years the development of a viable remote pull-in technique has become an important requirement for oil companies who are continuing to develop deeper and more marginal fields. The use of Remote Operated Vehicles (ROV's) can not only provide the required costs savings, but eliminates the risks to man.
Sonsub set out to design and build a system that was modular, could use the ROV for all subsea operations, and would only require minimal permanent subsea hardware support. These objectives were met with the completed system known as the Diverless Flowline Connection System (DFCS). The DFCS is capable of performing the tie-in of flowlines and umbilicals up to 18" O.D. The system is a light modular package that is easily handled and operated with any Work Class ROV in deepwater environments.
The system has been extensively tested under a wide variety of conditions and is ready to perform the tie-in of two 13.5" and 6" flowline in the South China Sea in early 1996. I n addition Sonsub have recently been contracted to perform the tie-in of 6 single bore flowlines ranging in size between 2.5" and 10", 14 multibore flowlines (2.5" and 8") and 4 umbilicals in the North Sea off the coast of Norway.
