Effects of column designs on the VIM response od deep-draft semi-submersible platform


Experiments regarding the Vortex-Induced Motions (VIM) phenomenon of deep-draft Semi-Submersible (SS) platforms were carried out in a towing tank in order to investigate the effects of two types of columns, i.e., rounded square sections and circular columns. Two different models at scale of 1:100 were built based on the typical geometry of a SS with four columns and each model with the same arrangement of four pontoons in closed configuration. The models were elastically mounted by means of a set of linear springs, which provide low structural damping. The range of towing velocities in the reduced velocity was 4 up to 25 covered Reynolds numbers from 7,000 to 80,000. Three angle of incidences for each model were tested, namely 0, 22.5 and 45 degrees related to the current incidence. Different VIM response was observed due to the column design. The maximum amplitude in the transverse direction was practically the same for both column designs, but occurring at different incidence angles, i.e., 0-degree for the SS with circular columns and 45 degrees for the one with rounded square columns. In terms of the yaw motions, the highest amplitudes were observed for the SS with circular columns for 22.5 and 45-degrees incidence, particularly around the reduced velocity based on yaw natural period equal to 8. On the other hand, yaw amplitudes increased continuously for the SS with rounded square columns, with no substantial difference related to the heading. These results confirmed that the heading effects on the VIM of SS strongly depend on the column design. The results presented herein are part of a more complete campaign of experiments carried out within the VIM JIP which is managed by MARIN and USP. Within this campaign, the effect of roughness on VIM response was also investigated using the same models. Those results can be found in a complementary paper in this conference.

GONÇALVES, Rodolfo Trentin; FUJARRA, André Luís Condin ; ROSETTI, Guilherme Feitosa ; KOGISHI, Andre Mitsuo ; KOOP, Arjen . Effects of column designs on the VIM response od deep-draft semi-submersible platform. In:  INTERNATIONAL OFFSHORE AND POLAR ENGINEERING CONFERENCE, 25., Kona, Hawaii-USA, 2015. Proceedings…. 7 p.

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