Flow induced vibrations play an important role in the process of fatigue in cylindrical elements of offshore platforms. One of the main sources of vibration is due to vortex shedding. Such vortices are originated from the separation of the boundary layer and the low-pressure regions cause the hydrodynamic forces to oscillate. This kind of vibration is known in literature as vortex-induced vibration (VIV), and it has some points that are not well understood yet. When a circular cross section is considered, the point of separation changes with the Reynolds number, increasing the complexity of the phenomena. Additionally, when two bluff bodies are disposed near each other, the vortices shed by one of them can reach the other, interfering with the vortex formation close to the later, and constituting another source of vibration. This work is an effort to provide a better comprehension of the vortex-induced vibration phenomena in a flow around groups of cylinders. In this paper, a detailed computational study of the flow around two rigid cylinders in a tandem arrangement is carried out. The spectral/hp element method is used in the simulations, with a modal decomposition in the span direction. The three-dimensional structures in the wake are analysed, and the level of synchronization of the flow along the span is verified for a gap of five diameters between the cylinders.

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