Vortex-induced vibration of floating circular cylinders with very low aspect ratio

摘要

Experiments regarding vortex-induced vibration (VIV) on floating circular cylinders with low aspect ratio were carried out in a recirculation water channel. The floating circular cylinders were elastically supported by a set of linear springs. Eight different aspect ratios were tested, namely L/D = 0.2,0.3,0.4,0.5,0.75,1.0,1.5 and 2.0. These aspect ratios were selected to cover the aspect ratio range of the main offshore circular platforms, such as spar and monocolumn. The aim was to understand the vortex-induced motions (VIM) of such platforms; due to this, the cylinders were floating, or m* =1. The range of Reynolds number covered 2800 Re 55,400. The amplitude results showed a decrease in amplitude with decreasing aspect ratio in the in-line and in the transverse directions. The frequency results confirm a different behavior for cylinders with L/D 0.5; in these cases, the cylinder free-end effects were predominant. The resonant behavior was no longer observed for L/D 0.2. The decrease in Strouhal number with decreasing aspect ratio is also verified, as well as for drag and lift forces. The added mass results help to identify the end of resonance for both directions, in-line and transverse. The amplitude results for the vertical direction, roll, pitch and yaw did not affect the VIV behavior.