The effect of base column on vortex-induced vibration of a circular cylinder with low aspect ratio

The end condition of a cylinder is known to influence its vortex-induced vibration (VIV) response. The design of a short circular cylinder with a concentric base column attached to its bottom is adopted by some floating structures for improved stability, but how the base column would affect the VIV of the cylinder has been rarely studied. In this paper, the VIV of an elastically mounted rigid cylinder with a base column and a low aspect ratio of 2 is investigated numerically by solving the Navier-Stokes equations. The numerical methods are validated against two existing VIV studies, including a 2D cylinder and a cylinder with a finite length. The impacts of the base column on the cylinder are analysed. It is found that although the free end effects associated with fluid flowing around the cylinder end are still present, attaching the base column leads to the expansion of the lock-in regime of the cylinder response. A relationship between non-dimensional response amplitude and lift coefficient is established, which takes into consideration the geometrical properties of the base column. By analysing the energy transfer from fluid to structure, the base column is also found to have significant damping effects on the cylinder response.