NDLI: Viscous Drift Forces on a Semi-Submersible Type Mega-Float Comprised of Circular Cylinders

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Sunahara, Shunji
Copyright Year	2004
Abstract	An estimation of the wave drift forces acting on a semi-submersible type Mega-float supported by very many columns is very important in order to design its mooring system. It is known that the wave drift forces acting on a train of multiple vertical circular cylinders may be determined using the potential flow theory. However, it has recently been reported that the large wave drift forces acting on a large scale model of a semi-submersible type Mega-float, comprised of many simple circular cylinders, for long wave periods, cannot be explained by the potential flow theory. In addition the forces seem to have a significant influence on the design of its mooring system. At first, it seemed that the measured forces were viscous drift forces. The viscous drift forces are in proportion to the square of the wave particle velocity or the cube of the wave height. Of course, the existence of viscous drift forces has already been established, but it was considered that the forces acting are conditional in that the flow is apt to shed, for example on complex under-water shapes, on radiation problem, in larger height or longer period waves. Also it was thought that the forces acting on simple circular cylinders were negligibly small from the viewpoint of engineering applications. Finally, it was not accurately verified that the forces were viscous drift forces. In this study, model tests were carried out. The wave loads acting on a 16-column platform model and the hydrodynamic forces acting on each column of the model were simultaneously measured. The contribution of the viscous drift force component on the wave drift force acting on a train of vertical circular cylinders was also investigated in detail. It was confirmed that significant viscous drift forces act on circular cylinders for long wave periods. Furthermore an applicable region of viscous and potential components of the wave drift forces acting on vertical circular cylinders was obtained.
Sponsorship	Ocean, Offshore, and Arctic Engineering Division
Starting Page	757
Ending Page	764
Page Count	8
File Format	PDF
ISBN	0791837459
DOI	10.1115/OMAE2004-51372
e-ISBN	0791837386
Volume Number	23rd International Conference on Offshore Mechanics and Arctic Engineering, Volume 3
Conference Proceedings	ASME 2004 23rd International Conference on Offshore Mechanics and Arctic Engineering
Language	English
Publisher Date	2004-06-20
Publisher Place	Vancouver, British Columbia, Canada
Access Restriction	Subscribed
Subject Keyword	Semi-submersible Circular cylinder Wave loads Viscous drift forces Mega-float Semi-submersible offshore structures Waves Circular cylinders Stress
Content Type	Text
Resource Type	Article

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