3.51 SMB METHOD FOR PREDICTING WAVES IN DEEP WATER
Révisions of earlier SMB forecasting curves are seen in Figures 3-15
and 3-16. The curves represent dimensional plots from the empirical
équations,
.
/gF\0,42
2- = 0.283 tanh 0.0125 M
U2
\U2/
—— = 1.20 tanh
2ttU
0.077
(3-21)
(3-22)
— = K exp
U
r
(3-23)
where
exp {x} =
In = lOge
K = 6.5882
A = 0.0161
B = 0.3692
C = 2.2024
and
D = 0.8798 .
With these relationships, the significant wave height Hp, and significant
wave period Tp, at the end of a fetch may be estimated when wind speed,
fetch length, and duration of wind over the fetch are given. Estimation
of wind parameters is discussed in Section 3.4, Wind Information Needed
for Wave Prédiction, following the évaluation of simplified prédiction
techniques. In using Figures 3-15 or 3-16 the estimated wind velocity U,
the fetch length F, and the estimated wind duration t, when a fetch
first appears on a weather chart, are tabulated. Figure 3-15 or 3-16 is
then entered with the value of U, using the scale on the left if U is
in knots, or the scale on the right if U is in statute miles per hour.
This U line is then followed from the left side of the graph across to
its intersection with the fetch length or F line, or the duration t
line, whichever cornes first.
3-35