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Wave radiation and wave diffraction from a submerged body in a uniform current

Published online by Cambridge University Press:  20 April 2006

John Grue  and
Enok Palm
John Grue
Affiliation:
Department of Mechanics, University of Oslo, Blindern, Oslo 3, Norway
Enok Palm
Affiliation:
Department of Mechanics, University of Oslo, Blindern, Oslo 3, Norway
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Abstract

Radiation and diffraction of free-surface waves due to a submerged body in a uniform current is considered. The fluid layer is infinitely deep and the motion is two-dimensional. Applying the method of integral equations, the radiation problem and the diffraction problem for a submerged circular cylinder are examined. For small speed U of the current a forced motion of a given frequency will give rise to four waves. It is shown, however, that, for a circular cylinder, an incoming harmonic wave gives rise to two waves only. Depending on the frequency, the new generated wave may be considered as a transmitted or a reflected wave. The mean second-order force is computed. For the radiation problem the first-order damping force is also obtained. It is shown that, for some values of the parameters, the damping force is negative. This result is closely related to the fact that a harmonic wave travelling upstream with a phase velocity less than U conveys negative energy downstream. The forces remain finite as Uσ/g (σ ≡ the frequency, g ≡ the acceleration due to gravity) approaches ¼.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 151 , February 1985 , pp. 257 - 278
Copyright
© 1985 Cambridge University Press

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