Effect of boundary condition and aspect ratio on vortex-induced vibration response of a circular cylinder

Abstract

A numerical study based on a wake oscillator model was conducted to determine the effects of boundary condition and aspect ratio on the vortex-induced vibration (VIV) response performance of a circular cylinder. The structural displacement, structural frequency, phase portrait, standing waves, travelling waves and lift force coefficient for five different boundary conditions and four aspect ratios were compared. The results showed that, when the aspect ratio is small, there are obvious differences between the VIV displacements of the cylinder with different boundary conditions. As the aspect ratio increases, the differences become smaller. For a small aspect ratio, the VIV displacements are dominated by the standing wave patterns along the total span of the cylinder. However, for a large aspect ratio, the VIV displacements are dominated by the standing wave and travelling wave patterns near the cylinder ends and midpoint, respectively. The VIV displacements vary with time and can be divided into three types: periodic vibration with only one peak frequency, quasi-periodic vibration with two peak frequencies, and chaotic vibration with many peak frequencies. The phase portraits can also be split into three types: an ellipse, two elliptical rings and many ellipses.