Experimental and numerical studies of the pontoon effect on vortex-induced motions of deep-draft semi-submersibles

• Published in: Journal of fluids and structures 2017-07, Vol.72, p.59-79
• Main Authors: Liu, Mingyue, Xiao, Longfei, Liang, Yibo, Tao, Longbin
• Format: Article
• Language: English
• Subjects: Deep-draft semi-submersible; Experimental study; Numerical simulation; Pontoon effect; Vortex-induced motion
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2017.04.007

The vortex-induced motion (VIM) is a critical issue in mooring and riser system design for column-type deepwater platforms. As regards to deep-draft semi-submersibles (DDS), even though VIM is mainly excited by vortex shedding around columns, the large-volume pontoons beneath the columns are also responsible for the wake interference, implying a non-negligible influence on VIM behavior. An experimental study and three-dimensional numerical simulations were performed to analyze the pontoon effect on the VIM of two semi-submersibles and a four-column structure without pontoons. The numerical results using Detached Eddy Simulation (DES) are in good agreement with the experimental measurements obtained from the towing model tests. The present investigations indicate that the resonant phenomenon is observed for all configurations. However, the four-column structure without pontoons shows the most significant transverse responses and yaw motions at both 0°- and 45°-incidences owing to the largest fluctuating lift forces induced by the well-established wake. Additionally, the negative values of work done by the pontoons at all reduced velocities confirm their damping effect on the VIM response. •Experimental and numerical studies on VIM of DDSs are performed.•We investigate the influence of pontoons on VIM behavior.•Motion responses, excitation loads, and spectral characteristics are discussed.•Pontoons can disturb the wakes of columns and consequently mitigate VIM response.•3-D numerical simulations using DES on VIM issue are reliable.