Vortex-induced motion of a free-standing riser below the critical mass ratio

Document Type

Conference Proceeding


American Society of Mechanical Engineers

Place of Publication

United States


School of Engineering




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.


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.



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