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CFD Analysis of Vortex-Induced Motions of Bare and Straked Cylinders in Currents

[+] Author Affiliations
K. P. Thiagarajan

University of Western Australia, Crawley, WA, Australia

Y. Constantinides

ChevronTexaco, Houston, TX

L. Finn

Technip Offshore, Inc., Houston, TX

Paper No. OMAE2005-67263, pp. 903-908; 6 pages
doi:10.1115/OMAE2005-67263
From:
  • ASME 2005 24th International Conference on Offshore Mechanics and Arctic Engineering
  • 24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 3
  • Halkidiki, Greece, June 12–17, 2005
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 0-7918-4197-9 | eISBN: 0-7918-3759-9
  • Copyright © 2005 by ASME

abstract

It is widely acknowledged that the use of helical strakes for mitigation of vortex-induced motions (VIM) of surface piercing cylinders, such as spar platforms, is only partially effective. Using computational fluid dynamics tools, we compare the oscillation characteristics of a bare cylinder and a straked cylinder in uniform currents. Our model comprised of a straked cylinder with diameter of 0.741 m, aspect ratio of 1:1.9 and three helical strakes of height 13% of cylinder diameter. This geometry corresponds to the hard tank geometry of a scaled truss spar model known to exhibit VIM in tow tank testing. In the CFD simulations the cylinder is moored with linear springs to provide a range of reduced velocities. The fluid domain is made of an unstructured grid comprising of hexahedral elements. Fluid structure interaction utilizes grid stretching and a user defined function for solving the equations of motion. Turbulence modeling uses Detached Eddy Simulation (DES) and the boundary layer is modeled using a wall function with a surface roughness of 0.0003 m. Reynolds numbers are in the range of 50,000 to 100,000. Results for straked cylinder compares reasonably with published results, but under-predicts the peak response. In comparing with corresponding results for a bare cylinder without strakes, the spectral features of the transverse displacement show variations, which are found to be due to the spoiling effect of the strakes.

Copyright © 2005 by ASME

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