Offshore Technology

Boundaries Effects on the Movements of a Sphere Immersed in a Free Surface Flow

[+] Author and Article Information
D. Mirauda

Department of Environmental Engineering and Physics, Basilicata University, viale dell’Ateneo Lucano 10, Potenza 85100, Italydomenica.mirauda@unibas.it

A. Volpe Plantamura

Department of Environmental Engineering and Physics, Basilicata University, viale dell’Ateneo Lucano 10, Potenza 85100, Italyantonio.volpeplantamura@unibas.it

S. Malavasi

Department of Environmental, Hydraulic, Infrastructures and Surveying Engineering, Politecnico di Milano, piazza Leonardo da Vinci 32, Milano 20133, Italystefano.malavasi@polimi.it

J. Offshore Mech. Arct. Eng 133(4), 041301 (Apr 07, 2011) (5 pages) doi:10.1115/1.4003276 History: Received June 23, 2009; Revised October 07, 2010; Published April 07, 2011; Online April 07, 2011

This work analyzes the influence of boundary conditions on the movements of a sphere immersed in a steady free surface flow. The sphere is free to move both in the transverse and streamwise directions and it is characterized by the values of the mass ratio m equal to 1.34 and of the damping ratio ζ equal to 0.004. In all the experiments the blockage coefficient is kept constant, while the sphere is located at different distances from the free surface and from the bottom wall of the channel. The movements of the sphere have been measured by means of the image analysis of a charge coupled device camera which provides the 2D (streamwise and transverse) displacements of the sphere with a temporal resolution of 0.02 s. The experimental data show a significant influence of the boundaries on the sphere movement and highlight a different behavior of the amplitude response between the three different experimental setups considered.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Normalized amplitude (Ax∗/Ay∗) versus m∗ for different tethered spheres. The ratio is measured for conditions of maximum Ay∗(7).

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Figure 2

Layout of experimental apparatus with sketch of the obstacle rest mounted on the channel (cross section)

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Figure 3

Trajectories of the sphere in water: (a) h∗=2; (b) h∗=3.97; and (c) h∗=0

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Figure 4

Normalized amplitude (Ax∗/Ay∗) versus m∗. The ratio is measured for conditions of maximum Ay∗. ○, data by Govardhan and Williamson (7); ●, present data (test 14)

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Figure 5

Amplitude ratios versus Re: (a) streamwise amplitude ratio Ax∗ and (b) transverse amplitude ratio Ay∗

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Figure 6

Evolution in the time of the transverse trajectories for Re=4.3×104: (a) test 14, (b) test 21, (c) test 7, (d) Strouhal number of the transverse oscillation Sy versus h∗, and (e) Ay∗ versus h∗, for Re=17,400, 34,800, and 43,500

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Figure 7

Strouhal numbers versus Re: (a) streamwise Strouhal number Sx and (b) transverse Strouhal number Sy




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