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Experimental observation of a near-motion-trapped mode: free motion in heave with negligible radiation

Published online by Cambridge University Press:  02 December 2015

H. A. Wolgamot
Affiliation:
Faculty of Engineering, Computing and Mathematics/UWA Oceans Institute, University of Western Australia, Crawley, WA 6009, Australia
P. H. Taylor
Affiliation:
Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK
R. Eatock Taylor
Affiliation:
Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK
T. S. van den Bremer
Affiliation:
Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK
A. C. Raby
Affiliation:
School of Marine Science and Engineering, Plymouth University, Plymouth PL4 8AA, UK
C. Whittaker
Affiliation:
School of Marine Science and Engineering, Plymouth University, Plymouth PL4 8AA, UK
Corresponding
E-mail address:

Abstract

A simple geometry that exhibits near motion trapping is tested experimentally, along with perturbed versions of the structure. The motion of the freely floating structure and the surrounding wave field is tracked and the near-motion-trapped mode is found, characterised by a slowly decaying heave motion with very small linear radiation of energy. It is found that the latter property is a better discriminator of the perturbed geometries as viscous damping masks fine differences in radiation damping as far as the motion of the structure is concerned. The magnitude of this viscous damping is reasonably well predicted by a simple Stokes oscillatory boundary layer analysis.

Type
Rapids
Copyright
© 2015 Cambridge University Press 

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Experimental observation of a near-motion-trapped mode: free motion in heave with negligible radiation
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