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Research Papers: Ocean Engineering

Hydroelasticity of Four Flexible Cylinders in Square Arrangement Subjected to Uniform Cross-Flow

[+] Author and Article Information
Bijan Sanaati

e-mail: sanaaty1@yahoo.com

Naomi Kato

e-mail: kato@naoe.eng.osaka-u.ac.jp
Department of Naval Architecture and Ocean Engineering,
Osaka University,
2-1 Yamadaoka,
Suita, Osaka, Japan

Contributed by the Ocean Offshore and Arctic Engineering Division of ASME for publication in the Journal of Offshore Mechanics and Arctic Engineering. Manuscript received March 27, 2012; final manuscript received August 29, 2012; published online February 25, 2013. Assoc. Editor: R. Cengiz Ertekin.

J. Offshore Mech. Arct. Eng 135(2), 021103 (Feb 25, 2013) (9 pages) Paper No: OMAE-12-1031; doi: 10.1115/1.4007596 History: Received March 27, 2012; Revised August 29, 2012

Groups of cylinders can be found in many engineering fields such as marine and civil applications. The behavior of the group cylinders can be very complex because it undergoes the mutual effects of adjacent cylinders arranged in different positions. In this paper, the results of a study on the dynamics of a group of flexible cylinders in square arrangements along with a single (isolated) cylinder subjected to uniform cross-flow (CF) are presented. Four flexible cylinders of the same size, properties, and pretensions were tested in two configurations with different center-to-center separations. Reynolds number ranged from 1400 to 20,000 (subcritical regime).The parameter of reduced velocity reached up to 19. The aspect ratio of all the cylinders was 162 (length/diameter). Mass ratio (cylinders mass/displaced water) was 1.17. The amplitude ratio of the CF vibration of the downstream cylinders, hydrodynamic force coefficients including mean and fluctuating components of the drag and lift forces, tension variation of the downstream cylinder, and frequency responses in both CF and inline (IL) directions were analyzed. All the cylinders excited up to the second and fourth mode of vibrations for CF and IL directions, respectively. Mean drag coefficient of the upstream cylinders are almost twice those of the downstream cylinders. The mean lift coefficient is much higher for the upstream cylinders than the downstream cylinders with different positive and negative signs. The IL and CF frequencies of the downstream cylinders are lower than those of the upstream ones and the single cylinder.

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Figures

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Fig. 1

A schematic of the test model setup

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Fig. 2

Four flexible cylinders in square arrangements: (a) the 1G configuration; (b) the 2G configuration

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Fig. 3

The vibration amplitude ratio (A*std) versus reduced velocity (Ur) for four group cylinders along with a single cylinder

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Fig. 4

The IL and CF frequency responses of the four multiple and single cylinders for the 1G configuration

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Fig. 5

The IL and CF frequency responses of four multiple and single cylinders for the 2G configuration

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Fig. 9

Fluctuating tension increased value (Tstd) of the P1cylinder at the 1G and 2G configurations along with the single cylinder

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Fig. 6

The hydrodynamic force coefficients of four multiple cylinders and single cylinder for the 1G configuration: (a) mean drag coefficient; (b) fluctuating drag coefficient; (c) mean lift coefficient; (d) fluctuating lift coefficient

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Fig. 8

Mean tension increased value (Tmean) of the downstream cylinder (P1) at the 1G and 2G cases along with that of the single cylinder

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Fig. 7

The hydrodynamic force coefficients of four multiple cylinders and single cylinder for the 2G configuration: (a) mean drag coefficient; (b) fluctuating drag coefficient; (c) mean lift coefficient; (d) fluctuating lift coefficient

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