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Design Aspects of Large Diameter Turret Systems: Part 1 — Moonpool Piston Mode

[+] Author Affiliations
Igor de Vries, Alexandre Barbagallo, Naciri Mamoun

SBM Offshore, Monaco

Bernard Molin

Ecole Centrale de Marseille, Marseille, France

Alexandre Cinello

OCEANIDE, La Seyne sur Mer, France

Paper No. OMAE2014-24531, pp. V01BT01A043; 10 pages
  • ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 1B: Offshore Technology
  • San Francisco, California, USA, June 8–13, 2014
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-4538-7
  • Copyright © 2014 by ASME


The maximum displacement of turret moored floating production and storage units (FPSO, FLNG) has been steadily increasing over the past decades and is likely to increase even further in the future. Furthermore, some of these turret moored units are designed to keep position in even the harshest of environments (e.g. 10,000-year storms) and very deep water (e.g. more than 2000m depth). As a consequence, the demands on the capacity of mooring systems are also increasing and larger turret sizes with relatively smaller chaintable openings result. The turret cylinder is neither completely open (due to strength considerations) nor completely closed (due to installation and inspection requirements). Therefore, the mass of water inside the turret will to a degree be forced to move with the turret, but also to a degree be able to enter and exit the turret. As a result, a combination of inertial, hydrostatic, and piston mode effects similar to those found in open moonpools can occur. An additional complicating factor is that the turret is surrounded by an open annular space which influences the flow of water around the turret bottom. Both piston mode and inertia of water inside the turret will impose additional loads on the turret and its support system. It is therefore imperative that these loads be taken into account in the design phase. A number of tools, both experimental and computational may be used to obtain estimates of loads. However, whichever method is chosen, a necessary step is to identify the natural periods of the piston mode taking place in the turret. Investigations, whether numerical or experimental, must obviously focus on these periods. In this paper, analytical, computational (CFD) and experimental methods to obtain natural piston mode periods of turret moonpools are described. The methods are applied to simplified, yet realistic, turret models. Results from these different methods are compared. Respective figures of merit are discussed.

Copyright © 2014 by ASME
Topics: Design , Pistons



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