Recently the semisubmersible has become a favorable choice as a wet-tree floating platform supporting steel catenary risers (SCRs), mainly due to its capability of quayside topside integration and cost-effectiveness. However, it is still a challenge for a conventional semisubmersible to support SCRs, particularly large ones, in harsh environment and relatively shallow water due to its large heave motion. To answer this challenge, a new semisubmersible design has been developed at Technip as a wet-tree floater which achieves significantly improved heave motion and vortex-induced-motion (VIM) performance through hull form optimization while maintaining the simplicity of a conventional semisubmersible design. The difference between the NexGen semi-submersible design and a conventional semi-submersible design is in the blisters attached to the columns, distribution of pontoon volume, and pontoon cross section shape. In the NexGen semi-submersible design, the pontoon volume is re-distributed to minimize heave loading while maintaining sufficient structural rigidity, a long heave natural period and adequate quayside buoyancy. The blisters attached to the columns effectively break the vortex shedding coherence along the column length and therefore suppresses VIM. The blisters also provide much needed stability at quayside and during the hull deployment process, making the hull design less sensitive to topside weight increase. In the present paper the hydrodynamic aspects of this new design are discussed in detail. A benchmark case is presented in which the new design is compared against a more conventional design with the same principal dimensions. It is shown that the heave response in extreme sea states (100-yr hurricane) at the platform center of gravity is reduced by about 30–40%, and at the SCR hang-off locations by about 25–30%. Due to the reduced heave motion, SCRs experience about one third less stress at the touchdown point. A qualitative VIM analytical model is used to predict the VIM suppression effect of the new design. A highlight of a VIM model test for the proposed design is also presented. The reduced heave and VIM significantly improve the riser stress and fatigue near the touchdown point. This new design makes the semisubmersible a more robust wet-tree floater concept, and even a potentially good candidate as a dry-tree host concept in relatively benign environment.
Skip Nav Destination
ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering
June 19–24, 2011
Rotterdam, The Netherlands
Conference Sponsors:
- Ocean, Offshore and Arctic Engineering Division
ISBN:
978-0-7918-4433-5
PROCEEDINGS PAPER
A New Semisubmersible Design for Improved Heave Motion, Vortex-Induced Motion and Quayside Stability
Qi Xu
Qi Xu
Technip, Houston, TX
Search for other works by this author on:
Qi Xu
Technip, Houston, TX
Paper No:
OMAE2011-49118, pp. 95-103; 9 pages
Published Online:
October 31, 2011
Citation
Xu, Q. "A New Semisubmersible Design for Improved Heave Motion, Vortex-Induced Motion and Quayside Stability." Proceedings of the ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. Volume 1: Offshore Technology; Polar and Arctic Sciences and Technology. Rotterdam, The Netherlands. June 19–24, 2011. pp. 95-103. ASME. https://doi.org/10.1115/OMAE2011-49118
Download citation file:
41
Views
Related Proceedings Papers
Related Articles
New Frontiers in the Design of Steel Catenary Risers for Floating Production Systems
J. Offshore Mech. Arct. Eng (November,2001)
An Enhanced Semi-Coupled Methodology for the Analysis and Design of Floating Production Systems
J. Offshore Mech. Arct. Eng (August,2021)
Dynamic Analysis as an Aid to the Design of Marine Risers
J. Pressure Vessel Technol (May,1978)
Related Chapters
Introduction and Definitions
Handbook on Stiffness & Damping in Mechanical Design
Fault-Tolerant Control of Sensors and Actuators Applied to Wind Energy Systems
Electrical and Mechanical Fault Diagnosis in Wind Energy Conversion Systems
Production Riser Life Extension – A Class Perspective
Ageing and Life Extension of Offshore Facilities