Experimental study of the column shape and the roughness effects on the vortex-induced motions of deep-draft semi-submersible platforms
Abstract
Experiments regarding the VIM of SS platforms with four columns were carried out to investigate the effects of the
surface roughness and the column shape. Two different geometry of columns were experimented: rounded-square
and circular-cross sections. Each model had the same arrangement of four pontoons in a closed configuration. The
range of reduced velocity was from 4 up to 25 covering Reynolds numbers from 7.000 to 80.000. Three angles of
incidences for each model were tested, namely 0, 22.5 and 45. For each model, three different levels of roughness
were tested. Regarding roughness effects the results seem to confirm two 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. Regarding the effect of the column shape, the results indicated that the
heading effects on the VIM of SS strongly depend on the column shape. The characteristic motion periods upheld
the resonance behavior for the motions in the transverse direction and yaw motions for the lock-in range. Heave,
roll and yaw motions did not impact the VIM behavior in the horizontal plane, and their amplitudes were not
considered relevant.
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Keywords
Vortex-induced motions (VIM), Deep-draft semisubmersible (DD-SS), Model tests, Roughness, Column shape
Authors
Rodolfo T. Gonçalves a,*,1
, Andre L.C. Fujarra b,1
, Guilherme F. Rosetti c,1
, Andre M. Kogishi d
, Arjen Koop e
a Department of Ocean Technology, Policy, and Environment, School of Frontier Sciences – The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa-shi, Chiba, 277-8561, Japan
b Department of Mobility Engineering, Joinville Campus – Federal University of Santa Catarina, Joinville, SC, Brazil
c Argonautica Engineering and Research, S ao Paulo, SP, Brazil ~
d IPT – Institute for Technological Research of the State of Sao Paulo, S ~ ao Paulo, SP, Brazil ~
e MARIN – Maritime Research Institute Netherlands, Wageningen, The Netherlands