© 1993 by Oxford University Press
ENERGY FLUX AND GROUP VELOCITY IN CURRENTS OF UNIFORM VORTICITY
,2
(
1Division of Applied Mechanics, University of Trondheim N-7034 Trondheim-NTH, Norway
2Department of Physics, Florida State University Tallahassee, Florida 32306, USA
)
Present address: IKU, SINTEF Group, N-7034 Trondheim, Norway.
Linear water waves superimposed on an opposing current varying linearly down to a depth h are investigated. Fluxes of mass, momentum, and energy are calculated. Of main interest is the expression for the energy flux and its possible decomposition into terms in such a way that the contribution from wave energy is clearly shown. Such a decomposition would link the kinematic group-velocity concept to the dynamic concept of velocity of propagation of wave energy. We write the energy flux in a form that generalizes the simple expression found by Brink-Kjaer for the case of a linear current extending down to the bottom. In this expression the term corresponding to the group velocity appears quite naturally, as the energy flux of pure wave energy.