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The mean drift force and yaw moment on marine structures in waves and current

Published online by Cambridge University Press:  26 April 2006

John Grue  and
Enok Palm
John Grue
Affiliation:
Department of Mathematics, Mechanics Division, University of Oslo, Norway
Enok Palm
Affiliation:
Department of Mathematics, Mechanics Division, University of Oslo, Norway
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Abstract

The effect of the steady second-order velocities on the drift forces and moments acting on marine structures in waves and a (small) current is considered. The second-order velocities are found to arise due to first-order evanescent modes and linear body responses. Their contributions to the horizontal drift forces and yaw moment, obtained by pressure integration at the body, and to the yaw drift moment, obtained by integrating the angular momentum flux in the far field, are expressed entirely in terms of the linear first-order solution. The second-order velocities may considerably increase the forward speed part of the mean yaw moment on realistic marine structures, with the most important contribution occurring where the wave spectrum often has its maximal value. The contribution to the horizontal forces obtained by pressure integration is, however, always found to be small. The horizontal drift forces obtained by the linear momentum flux in the far field are independent of the second-order velocities, provided that there is no velocity circulation in the fluid.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 250 , May 1993 , pp. 121 - 142
Copyright
© 1993 Cambridge University Press

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