CFD Simulation of Vortex-Induced Vibration of a Flexible Riser With Buoyancy Module Under Uniform Flow Using a Two-Way Coupled Model

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Abstract The buoyancy modules are generally used as an attachment to the risers to increase the axial tension, such as top tensioned drilling risers. Consequently, these modules change the fluid-structure interaction, leading to a change in the response characteristics. Literature indicates limited information on the VIV response characterization of the flexible riser with the buoyancy module. An investigation into the VIV characteristics of flexible risers with buoyancy modules has been carried out and presented in this article. The buoyancy module geometry is one of the important parameters influencing the VIV response of the flexible riser. The study was conducted using a two-way coupled fluid-structure interaction model including the influence of buoyancy module length on the VIV response of flexible riser for L/D = 100, m* = 2.55, and EI = 2.95 at various reduced Velocity (Vr) in uniform current using CFD simulation. The time domain results obtained from CFD simulation such as force coefficients and VIV responses are converted into frequency domain responses using Fast Fourier Transform (FFT). It was observed that the inline and crossflow displacement responses showed double peak frequency responses. It is observed that the lower frequency corresponds to the riser with a buoyancy module and the higher frequency corresponds to the bare riser. The buoyancy module acts as a response controller in the crossflow direction, and the buoyancy module dominates the VIV response at a lower reduced velocity (Vr). The excitation of the lower frequency component is diminished as the Vr increases, and it shows that the bare riser dominates the riser VIV. However, the inline RMS response of the flexible riser with a buoyancy module is higher than the bare riser.