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Offshore and Structural Mechanics

# Theoretical and Experimental Study on a Porous Cylinder Floating in Waves

[+] Author and Article Information
Fenfang Zhao

Institute of Industrial Science, University of Tokyo, Tokyo, Japan; College of Fisheries, Ocean University of China, Qingdao, Chinazhaoff@ouc.edu.cn

Weiguang Bao, Takeshi Kinoshita, Hiroshi Itakura

Institute of Industrial Science, University of Tokyo, Tokyo, Japan

J. Offshore Mech. Arct. Eng 133(1), 011301 (Nov 03, 2010) (10 pages) doi:10.1115/1.4001435 History: Received May 21, 2009; Revised December 16, 2009; Published November 03, 2010; Online November 03, 2010

## Abstract

In the present work, theoretical and experimental studies on the interaction of water waves with a truncated circular cylinder were performed. The cylinder, which is partly made of porous materials, possesses a porous sidewall and an impermeable bottom. A nondimensional parameter $b$ is adopted in the theoretic formulation to describe the porosity, which is not directly related to the opening ratio $τ$ of the porous materials. To validate the theoretical work and computed results, a series of model tests are carried out in a wave basin. Effort is made to establish an empirical relation between $b$ and $τ$ based on the comparison of the calculation and experimental data. The phenomenon of the sloshing mode that occurred at a certain wave number is observed, which might have an application in breakwaters. The validation of the Haskind relations is examined for the porous body. It is found that the damping coefficient consists of two parts. In addition to the component of conventional wave-radiating damping, there exists a second component caused by the porous effects.

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## Figures

Figure 1

Sketch of the cylinder and division of the fluid domain

Figure 2

General view of the experimental setup

Figure 3

Comparison of experimental results with computed results for d/a=2.0: (a) surge exciting force; (b) heave exciting force; and (c) exciting pitch moment

Figure 4

Hydrodynamic coefficients in surge for d/a=2.0: (a) added mass λ11; (b) damping μ11

Figure 5

Comparison of the experimental data with the computed results of the hydrodynamic coefficients in the heave for d/a=2.0: (a) added mass λ33; (b) damping μ33

Figure 6

The relationship between the nondimensional porosity parameter b and the opening ratio τ of the model materials

Figure 7

Comparison of the experimental results with the computed results of the wave-exciting force in the surge direction with different wave slopes for d/a=2.0

Figure 8

The relationship of coefficient A and wave slope ε

Figure 9

Nondimensional damping against the dimensionless wave number for d/a=2.0 and b=9.0: (a) μ11; (b) μ33; (c) μ55; and (d) μ15(μ51). The asterisks represent the sum of porous and wave-radiating dampings.

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