Vortex-Induced Motion: Model Testing of a Monocolumn Floater

Abstract

The vortex-induced vibrations - VIV have been studied for several fields of engineering due to its occurrence in different structures, such as electrical cables, industries chimneys and offshore risers. Although available an extensive literature describing its fundamental issues, these vortex-induced phenomena still deserve investigation, particularly in the offshore platforms installed in regions with high current speed. Recently, the Vortex-Induced Motions - VIM, a particular case of vortex-induced vibration with high magnitude of response amplitude, have been observed in SPAR platforms installed in Gulf of Mexico - GoM, opening a new investigation field. For those motions, aspects such as asymmetric mooring restoring stiffness and the probable three-dimensionality of the flow turn the problem even more complex. Since 2003, in partnership with University of Sao Paulo and consultant companies, PETROBRAS has been studying the use of monocolumn floaters for oil production in Campos Basin and GoM. Considering the environmental conditions in these areas and assuming that monocolumn floaters can exhibit similar VIM behavior of SPAR platforms, it was started an experimental investigation focusing on VIM responses of small-scale monocolumn floaters in towing tank. Although based on the state of art procedures used for SPAR platforms, the monocolumn experiments considered the different geometry of this concept and the larger susceptibility to the three-dimensional effects, due to the smaller relation draft/beam. Special attention was given to the ratio roughness/beam in order to guarantee similarity between the experiments and its respective real cases. Additionally, different heading conditions were also tested. Thus, the present work presents a set of preliminary results and discussions concerning VIM of monocolumn floaters and its impact on the mooring line design and riser specification.

Recent structural design considerations related to floating production systems

“…Hence, an experimental investigation was started which focused on VIM responses of small-scale monocolumn floaters in a towing tank. Cueva et al (2006) considered environmental conditions for the Campos Basin and GoM and presented a set of preliminary results. In accordance with other VIM studies, the strong influence of the heading in VIM was noted, increasing the maximum cross flow amplitude from 0.8 to 1.2D.…”

Experimental Comparison of Two Degrees-of-Freedom Vortex-Induced Vibration on High and Low Aspect Ratio Cylinders with Small Mass Ratio

“…According to Gonçalves et al [7], in 2005 a partnership between the research group from USPUniversity of São Paulo and Petrobras started a pioneer and intensive experimental research on VIM of monocolumn platforms. Cueva et al [8], Fujarra et al [9], and Gonçalves et al [10] established experimental procedures for VIM tests on monocolumns, besides proposing a more accurate technique for analyzing the outcomes. Moreover, even for very low aspect ratios, the research showed that VIM on monocolumns also presents large amplitudes of transversal motion above reduced velocities of 4.…”

A Coupled Wave-Current-Structure Study for a Floating Offshore Wind Turbine Platform

“…VIM of cylinders and monocolumn platforms has been widely studied [1][2][3][4][5], which is found to be deeply related to its structural natural frequency and vortex shedding frequency. The vortex-induced vibration (VIV) response is also studied, and the classic 8-shaped orbital trajectories are found for typical cases.…”