INFLUENCE OF STIFFNESS RATIO ON VORTEX-INDUCED VIBRATION OF CYLINDER WITH LOW ASPECT RATIO

Author(s)

Gambarine, Dennis M. ; Minioli, Luiz E. B. ; Goncalves, Rodolfo T. ; Kogishi, Andre M. ; Fujarra, Andre L. C. ; ASME

• Document type: Journal article
• Source: PROCEEDINGS OF THE ASME 37TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING, 2018, VOL 2; v. N/A, p. 9-pg., 2018-01-01.

Abstract

Concern over the Vortex-induced Motions (VIM) acting on offshore structures, with special focus on monocolumn and spar platforms, mooring systems have crucial importance on system movements; the system has thus been transformed into a concept study herein. A floating and rigid circular cylinder with low aspect ratio (L/D=2) was used in the experiments carried out to investigate the influence of stiffness ratio (k(x)/k(y)) on Vortex-Induced Vibration (VIV). The cylinder was mounted in an elastic base composed of four springs with differences in in-line and transverse stiffness, defining: k(x)/k(y) congruent to 0.3, 0.5, 1.0, 2.0 and 3.0. The Reynolds number analysed belongs to a range between 0.2 . 10(4) and 2 . 10(4). Some good qualitative and quantitative agreements are found for in-line amplitudes, and higher k(x)/k(y) systems demonstrate significant oscillation for low relative velocities. This variation can be seen and justified when the XY-plane trajectories were plotted. When k(x)k(y) is defined as 2 and 3, the traditional VIV 8-shape is illustrated for reduced velocities between 3 and 6. In contrast, the other stiffness systems do not show significant movements and, consequently, a negligible XY shape. Roll and pitch degrees of freedom have shown the motions coupled with the transverse and the in-line motions respectively. Moreover, the yaw motion did not present considerable angles. k(x)/k(y) = 2 has presented the highest lift force coefficients, without a great difference from the other aspects ratios, though. The drag force coefficient showed constant values for k(x)/k(y) = 2 and 3, the smallest results were observed for the system k(x)/k(y) =3. (AU)

• FAPESP's process: 14/02043-1 - Behavior of oil platforms under the action of VIM and simultaneous wave incidence
• Grantee: Rodolfo Trentin Gonçalves
• Support Opportunities: Scholarships in Brazil - Post-Doctoral