Vortex-induced motion of a free-standing riser below the critical mass ratio
Document Type
Conference Proceeding
Publisher
American Society of Mechanical Engineers
Place of Publication
United States
School
School of Engineering
RAS ID
25923
Abstract
The presented work studied the vortex-induced motion (VIM) response of a free-standing riser (FSR) with varied riser length and buoyancy can (BC) mass with an ultimate aim to find a combination that would reduce the motion of the system. Specifically, four model configurations were experimentally tested in a flume tank over a range of flow velocities, with the BC motion recorded by a submersible camera positioned directly above the model; consequently, inline (IL) and crossflow (CF) amplitudes were estimated with a motion tracking software. In the pre-resonant flow regime, non-dimensionally, minimal differences were observed between the CF amplitudes, and the IL motion was reduced with a longer riser. Given the extreme length of full-scale FSRs and inherent low natural frequency, it is impractical to increase the riser tension to a point where VIM would not occur under normal environmental conditions. Alternatively, increasing the mass ratio of the BC so that it is above the critical mass ratio of 0.54 (the ratio of the mass of the body to the mass of the fluid) would limit the resonant flow velocities to a finite range, but a larger BC may not be an economically viable solution, and because of the increased diameter, it would experience a larger CF amplitude during resonance. Further study into the prevention of VIM of an FSR by varying the riser length and BC mass is unlikely to be beneficial.
DOI
10.1115/OMAE2017-61399
Access Rights
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Comments
Florager, C., & Balash, C. (2017, June). Vortex-Induced Motion of a Free-Standing Riser Below the Critical Mass Ratio. In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering (pp. V002T08A032-V002T08A032). American Society of Mechanical Engineers. Available here.