Investigation on vortex-induced motions of four-square columns in a square configuration considering galloping under different current velocity and incident angle

Abstract

The study of vortex-induced motions (VIM) is practical significance for offshore oil and gas development. The VIM of multi-column structures, which has not been completely understood, is more complex compared to that of an isolated column structures. The VIM of four rigidly coupled square columns in a square configuration was investigated numerically using Reynolds-averaged Navier–Stokes (RANS) equations with the SST k–ω turbulence model for incident angles of α = 0°, 15°, 30°, and 45°. The time histories of the displacement, the motion amplitudes, the frequency characteristics, the hydrodynamic forces, the motion trajectories, and the vortex flow patterns were analyzed and discussed. The results indicate that the motion behavior of the four-square columns structure is more likely to be a combined motion of VIM and galloping. More specifically, the critical reduced velocities for occurrence of sway and surge galloping are both approximately 9.23, while yaw galloping may occur at a lower reduced velocity. It is found that the complex motion frequency components cause irregular motion trajectories and vortex flow patterns in the pre-lock-in and post-lock-in cases; but unitary motion frequency components lead to regular motions in the lock-in cases. Additionally, there is a strong coupling relationship between the sway and yaw motion, which is independent of the incident angle.