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arXiv:1401.1682physics.flu-dyn

Ship waves in the presence of uniform vorticity

Simen Å. Ellingsen

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Abstract

Lord Kelvin's result that waves behind a ship lie within a half-angle 19 deg 28' is perhaps the most famous and striking result in the field of surface waves. We solve the linear ship wave problem in the presence of a shear current of constant vorticity S, and show that the Kelvin angles (one each side of wake) as well as other aspects of the wake depend closely on the "shear Froude number" Frs=VS/g (based on length g/S^2 and the ship's speed V), and on the angle between current and the ship's line of motion. In all directions except exactly along the shear flow there exists a critical value of Frs beyond which no transverse waves are produced, and where the full wake angle reaches 180 deg. Such critical behaviour is previously known from waves at finite depth. For side-on shear, one Kelvin angle can exceed 90 deg. On the other hand, the angle of maximum wave amplitude scales as 1/Fr (Fr based on size of ship) when Fr >> 1, a scaling virtually unaffected by the shear flow.

arXiv comments
10 pages, 6 figures, accepted for J. Fluid Mech. Rapids
Journal reference
J. Fluid Mech. (JFM Rapids) 742 R2 (2014)
DOI
doi:10.1017/jfm.2014.28
Subjects
physics.flu-dynFluid Dynamics

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  1. The Erdos Paradox 1 comment
    • There's plenty examples indeed if you just dig around. I have a colleague who published a theoretical paper [0] in one of the top fluid mechanics journals 5 years back. That paper originated from his lecture notes in a course that he gave for the first time, where in one part he…

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