Experiments and numerical simulations are carried out to investigate the flow-induced vibration of an elastically-supported, circular cylinder placed near a plane boundary. The flow field is visualized using the hydrogen bubble technique. Two modes of flow-induced oscillations are recognized, namely fore-backward oscillation at lower flow speeds, and transverse oscillation at higher flow speeds. In numerical simulations, the Navier-Stokes equations for unsteady incompressible viscous flow combined with a k-ω turbulence model are solved via finite element method. Arbitrary Lagrangian-Eulerian (ALE) method using an overlapping grid system is used to capture the motion of the cylinder.
The vortex induced vibration (VIV) of pipelines is a major topic in coastal and offshore engineering since it may lead to fatigue destruction of pipelines, causing tremendous economic losses and environmental disaster. So far, many experimental and numerical investigations on VIV problems have been conducted, most of them concerning isolated pipelines, usually represented by circular cylinders in research, such as Mendes and Branco (1999), Zhou and So et al. (1999), etc. On the other hand, for the VIV problem of pipelines near the seabed, there is far less literature available than there is for the isolated pipeline case. With the presence of seabed, the flow is constrained by the bottom boundary. Previous surveys of flow around a fixed cylinder reveals that when the gapto- diameter ratio decreases to less than 0.3, the regular vortex shedding is suppressed. Chen and Su (2011) investigate the whole procedure from ignition to the steady stage of the flow around a circular cylinder above planar boundary; found that vortex shedding does happen at the starting flow stage even though the gap ratio is less than 0.3. A few cycles of vortex shedding may happen before the final steady flow state is reached for small gap ratios.
