| Abstract | dc.description.abstract | The wave friction factor is commonly expressed
as a function of the horizontal water particle semi-excursion
(Awb) at the top of the boundary layer. Awb, in turn, is
normally derived from linear wave theory by UwbTw
2p , where
Uwb is the maximum water particle velocity measured at the
top of the boundary layer and Tw is the wave period.
However, it is shown here that Awb determined in this way
deviates drastically from its real value under both linear and
non-linear waves. Three equations for smooth, transitional
and rough boundary conditions, respectively, are proposed
to solve this problem, all three being a function of Uwb, Tw,
and δ, the thickness of the boundary layer. Because these
variables can be determined theoretically for any bottom
slope and water depth using the deepwater wave conditions,
there is no need to physically measure them. Although
differing substantially from many modern attempts to
define the wave friction factor, the results coincide with
equations proposed in the 1960s for either smooth or rough
boundary conditions. The findings also confirm that the
long-held notion of circular water particle motion down to
the bottom in deepwater conditions is erroneous, the motion
in fact being circular at the surface and elliptical at depth in
both deep and shallow water conditions, with only
horizontal motion at the top of the boundary layer. The
new equations are incorporated in an updated version
(WAVECALC II) of the Excel program published earlier
in this journal by Le Roux et al. Geo-Mar Lett 30(5): 549–
560, (2010). | es_CL |
