DESIGN AND HYDRODYNAMIC PERFORMANCE ANALYSES OF A LARGE SIMPLE BARGE
James Hamilton and John A. Mercier, Brown &Root
ABSTRACT
Effective innovations are simple. For floating production systems, a simple square barge configuration can provide a production and storage system which will enable a cost effective field development. The innovative aspects of this version of the Floating Production Storage and Off loading (FPSO) concept include avoidance of the turret mooring system, which allows a ship-shaped vessel to weather vane, avoidance of high- pressure multi-path fluid swivels, which provide flow paths from the subsea wells to the process plant on board the vessel, and the adoption of a structurally simple and construction friendly hull. The barge system, called a BARBOX, is spread moored so that it can resist severe weather from many different directions.
The paper will provide an account of the design and analyses used to configure this system for a central North Sea development. First, a brief overview of t he system and t h e design requirements for a medium-sized oil development will be provided.
The role of forces and motions caused by the actions of wind, waves and currents are then presented for this configuration. Design trade-offs related to ballast, storage and operational practices affecting natural periods of roll, pitch and heave are illustrated. Model tests provide basic information for motions and mooring analyses; a number of correlation studies related to slow drift motions, damping estimates and diffraction theory predictions (including drift forces with and without currents) will be presented. These results are used to determine freeboard requirements and slow drift. Anomalous roll motions observed during tests with large damping skirts (similar to bilge keels) around the base of the model will be described and discussed in terms of Matthieu instabilities. Techniques for minimizing mooring system costs will be presented.
Market forces are causing a rapid expansion of FPSO use and the concept examined in this paper is a solid candidate for applications. While the BARBOX configuration looks, and in many respects is, quite simple, the assessment presented shows that the design must be thoughtfully developed, to achieve good performance results.
