EM 1110-2-1100 (Part II)
30 Apr 02
EXAMPLE PROBLEM II-1-6
FIND:
Applicable wave theory for waves in (a) and (b). Which of these waves is a long wave?
GIVEN:
(a). d = 15 m, H = 12.2 m, T = 12 sec; (b). d = 150 m, H = 30 m, T = 16 sec.
SOLUTION:
(a) Calculate dimensionless parameters necessary for using Figure II-1-20. These are
d
. 0.01
gT 2
H
. 0.009
2
gT
H
' 0.8
d
m
gd . 12
sec
UR . 55
From Figure II-1-20, the applicable theory is cnoidal.
(b) In a similar fashion, compute
d
. 0.06
gT 2
H
. 0.01
2
gT
H
' 0.2
d
m
gd . 40
sec
UR . 1.5
With these values, Figure II-1-20 indicates the applicable theory is Stokes third- or fifth-order. It is noted
that the linear theory is also applicable.
Based on the values of Ursell parameter, neither wave (a) or (b) is a true long wave. Wave (a) may be
considered a long wave in comparison to wave (b).
II-1-60
Water Wave Mechanics
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