• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.9-15
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• 2015

We investigated the Reynolds number effects on the flow over a twisted offshore structure in the range of 3×10³≤ Re ≤ 1 × 10⁴. To analyze the effect of the twisted surface treatment, a large eddy simulation (LES) with a dynamic subgrid model was employed. A simulation of the cylindrical structure was also carried out to compare the results with those of the twisted offshore structure. As Re increased, the mean drag and lift coefficient of the twisted offshore structure increased with the same tendency as those of the cylindrical structure. However, the increases in the mean drag and lift coefficient of the twisted offshore structure were much smaller than those of the cylindrical structure. Furthermore, elongated shear layer and suppressed vortex shedding from the twisted offshore structure occurred compared to those of the cylindrical cylinder, resulting in a drag reduction and suppression of the vortex-induced vibration (VIV). In particular, the twisted offshore structure achieved a significant reduction of over 96% in VIV compared with that of the cylindrical structure, regardless of increasing Re. As a result, we concluded that the twisted offshore structure effectively controlled the flow structures with reductions in the drag and VIV compared with the cylindrical structure, irrespective of increasing Re.

• Journal of Ocean Engineering and Technology
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• v.32 no.4
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• pp.237-243
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• 2018

Recently, it was predicted that the size of offshore markets will grow as gas prices edge up. This paper presents experimental results for using strings as a suppression device on a circular cylinder and discusses the various data. A test model was used to investigate the role of strings by varying the thickness of the strings used to suppress a cylinder's lateral force taking into account the effect of turbulence promoted. A substantial amount of experimental data were taken from experiments performed on cylinders at Reynolds number up to a maximum value of $10^5$. The suppression of vortex shedding and a lateral force reduction of up to 70% were observed for the cylinder with strings.