Vortex-Induced Vibration (VIV) is the main source of riser pipes' fatigue damage. And vibrations are more complicated in side-by-side and tandem arrangements comparing to the vibration of the isolated pipe. In this paper, the numerical simulation is carried out by viv-FOAM-SJTU solver to analyze the Vortex-Induced Vibrations of two flexible pipes experiencing a Stepped Current, in side-by-side and tandem arrangements. In order to study its effects on the vibrational behaviour of both pipes, the spacing between them has been varied from 3 to 7 in side-by-side arrangement and 1 to 7 in tandem arrangement. In the first situation, the effect between pipes results in the enhancing of the vortex shedding. In tandem situation, the upstream pipe contributes a non-negligible effect to the vibration of the downstream pipe, even the dominant mode has been altered.
Vortex-Induced Vibration (VIV) is a critical concern for the offshore industry. At present, most researches in VIV of risers mainly consider the situation of isolated pipe. However, in actual production process, pipes are in side-by-side and tandem arrangements, and the interaction exists in adjoining pipes. As a result, the neglect of effects between pipes in numerical simulations will make the prediction of VIV inaccurately.
Huera-Huarte and Gharib (2011) conducted experiments on flow-induced vibration with wake interference of two flexible circular cylinders in side-by-side arrangement, in a uniform cross-flow. They found that the vibrations of these two cylinders exhibited wake-coupled VIV (WCVIV), when the centre-to-centre separations are less than 3.5 diameters. For separations larger than that, cylinders showed no synchronized motions, suggesting that the coupling was very weak.
Huera-Huarte and Bearman (2011) performed experiments of vortex-induced vibration of two flexible circular cylinders in tandem arrangement. They found that the upstream cylinder experienced larger vibrations than the downstream cylinder for small gap distances, when the excitation frequency was close to the natural frequency of the cylinder. The downstream cylinder showed non-classical VIV resonance or wake-induced vibration (WIV), while WIV was expected to be the main source of excitation.
