ABSTRACT

Previous studies have shown that vortex-induced motions of a cylindrical spar structure can be fundamentally different from a cylindrical FPSO (e.g., Sevan FPSO). Under similar environments, the primary difference between the two structures affecting vortex shedding is the aspect ratio (length to diameter ratio, L/D). The focus of this paper is to study vortex-induced vibration (VIV) generated from an elastically mounted cylinder by varying aspect ratio. Experiments have been conducted in a closed towing facility at The University of Western Australia to measure the response amplitude, hydrodynamics forces, Strouhal number, and the lock-in region while varying the aspect ratio of the cylinder from L/D=13 to L/D=0.5. The experimental result showed a significant effect of the aspect ratio on the response amplitude, drag and lift force, and Strouhal number. Response amplitude of the structure was observed to decreased as the aspect ratio reduced. It was found that the decrease on response amplitude is accompanied by a decrease in correlation length of vortex shedding. The decreasing trend is also followed by the results measured for drag and lift force. Comparisons with experimental results obtained from literature are presented in this paper. Case studies demonstrated the difference in VIV behaviour between a Sevan FPSO and a classic spar.

Keywords:
aspect ratio, cylindrical structure, experiment 1, frequency, vibration frequency 0, williamson, amplitude, mechanics, fpso, vortex
Subjects:
Offshore Facilities and Subsea Systems, Floating production systems
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2013. International Society of Offshore and Polar Engineers
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