PASSIVE CONTROL OF VORTEX-INDUCED MOTIONS ON DEEP-DRAFT SEMISUBMERSIBLE PLATFORMS

Abstract

The deep-draft semisubmersible (DDSS) platform is well known due to its favourable vertical motion routine. However, DDSS platforms face a serious challenge in vortex-induced motion (VIM) due to the changing forces of the column. A computational fluid dynamic (CFD) simulation using AcuSolve is conducted to investigate the effect of a twisted-square column with different twisted angles, 0°, 22.5°, 45.0°, 67.5° and 90.0°, on the VIM responses and performance at current incidence angles of 0° and 45°.Platform models at a scale of 1:70 are studied to determine that the alteration of vortex shedding due the separation line at the twisted column expressively influences the mean and fluctuation of hydrodynamic forces and motion. In particular interest is the drag and lift coefficients, surge, sway amplitudes, as well as the yaw motion of the DDSS platform. The simulation was conducted at a velocity of 0.16 m/s.