Roughness effects on the VIM response of deep-draft semi-submersible platforms


Experiments on the Vortex-Induced Motions (VIM) acting on deep-draft Semi-Submersible (SS) platforms were carried out in a towing tank in order to investigate the roughness effects on the surface of two different 1:100-scale models. Both models were built based on the typical SS geometry with four columns and each model with the same arrangement of four pontoons in closed configuration. The models were elastically supported by means of a set of linear springs, which also provided low structural damping, and then submitted to a range of towing velocities in the reduced velocity range from 4 up to 25 covering the Reynolds numbers from 7,000 up to 80,000. Three different levels of roughness were tested: 1) bare models; 2) intermediate level of roughness and 3) high level of roughness. For the SS with rounded square columns, no significant differences were observed in terms of the VIM response For the SS platform with circular columns, some difference on the transverse and yaw motions were observed. These results seem to confirm two important aspects: the important role played by the separation point near the rounded corners of the rounded-square columns and the roughness effect on the boundary layers of the circular columns at the Reynolds numbers just below the critical regime. The results presented herein are part of a more complete campaign of experiments carried out within the VIM JIP which is run by MARIN and USP. Also within this campaign, the effect of column design on VIM response was investigated using the same models. Those results can be found in a complementary paper in this conference.

FUJARRA, André Luís Condin; GONÇALVES, Rodolfo Trentin ; ROSETTI, Guilherme Feitosa ; SILVA JUNIOR, Hélio Correa da . Roughness effects on the VIM response of deep-draft semi-submersible platforms. In: INTERNATIONAL OFFSHORE AND POLAR ENGINEERING CONFERENCE, 25., Kona, Hawaii-USA, 2015. Proceedings…. 7 p.

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