INVESTIGATION ON THE CHARACTERISITICS OF VORTEX INDUCED MOTION OF A DEEP SEA MUTI-COLUMN FLOATING PLATFORM

Based on the impressible Navier-Stokes equation, the characteristics of the vortex induced motion (VIM) for a multi-column floating platform are investigated by employing an improved delayed detached eddy simulation method (IDDES). Mesh parameters and boundary condition developed in the numerical method are extensively studied. The transverse and yaw motion responses of a Tension Leg Platform (TLP) with four columns are computed in three current headings including 0°, 22.5°and 45°, for di erent reduced velocities. In addition, the behavior of vortex induced motion response, the frequency ratio and the displacement power spectral density are computed and systematically analyzed. The numerical results show that the present predictions of VIM agree well with those from experiments. The lock-in frequency occurs in the transverse reduced velocities ranging from 7.0 to 14.0 and the transverse motion amplitudes vary between 0.2D and 0.4D (where D denotes the width of the column). The yaw motion amplitudes increase with the reduced velocities, which may be related with galloping. It is also found that the transverse motion frequency is the same as the yaw response frequency as the excited yaw moment is governed by the lift force acting on the vertical columns. The frequencies of motion in 22.5° and 45° incidences are higher than that in 0° . However, the yaw motion energy in 22.5° and 45° are around 10% of that in 0 incidences. Further, the three-dimensional fluid pattern is analyzed in the process of VIM for a multi-column floating platform.