Session: 04-01-01 Flexible Pipes and Umbilicals I

Paper Number: 80601

80601 - A Numerical Investigation on Flow Induced Vibration of Flexible Risers in Tandem Arrangements 

In this work, a numerical simulation of flow-induced vibrations (FIV) of two tandem long flexible risers is performed. The numerical formulation consists of solving variational stabilized finite element based three-dimensional turbulent fluid equations coupled with linear modal analysis of Euler-Bernoulli beam equation for the riser. Computations are performed for two identical risers with an aspect ratio of 350 and mass ratio of 1.90, subjected to uniform velocity at a Reynolds number of 6400. The effect of the gap between the risers on the vortex-induced vibrations (VIV) is investigated. The gap ranges from 4 to 16 times the riser diameter. The displacement time history of the risers is computed in both cross-flow (CF) and in-line (IL) directions and compared with the experimental results available in the literature. A reasonable agreement between the simulation and the experiments is obtained. It is observed that the FIV response of the upstream riser roughly resembles the typical VIV response of a single/isolated riser. Investigation on displacement time histories, dominant frequencies, trajectory along the riser span, and vortex interactions are studied in detail. The upstream riser is observed to oscillate at higher modes than the downstream riser which shows the decrement in reduced velocity of the flow near the downstream region. The vortices in the wake of the upstream riser interact with the downstream riser resulting in rapid oscillations of the downstream riser. Higher harmonics, i.e., second and third harmonics are observed in the frequency analysis of the CF and IL displacement components. The shielding effects experienced by the downstream riser due to the wake generated by the upstream riser and its effect on the riser response has also been studied thoroughly for different gap ratios.

Presenting Author: Arun Periyal IIT Kharagpur

Authors:

Arun Periyal IIT Kharagpur
Ritwik Ghoshal IIT Kharagpur
Vaibhav Joshi Birla Institute of Technology & Science Pilani