Civil Engineering Reference
In-Depth Information
Water particle velocity and acceleration are functions of wave height, wave
period, water depth, distance above the sea bottom and time.
●
The most elementary wave theory was presented by Airy in 1845.
●
Another widely used theory, known as the stream function theory, is a
nonlinear solution similar to the Stokes fifth-order theory.
●
Figure 2.9
presents an example of the principal wave directions in the Gulf of
Mexico (GoM) through 290
read clockwise (i.e., wave directions applied to the
platform from the north, northeast, east, southeast, and so on through eight direc-
tions as wave height versus water depth). Note that the principal wave direction,
with the maximum wave height value, will be defined in the metocean report for
the location of the platform. Based on API-RP2A, a reduction factor should be
applied on the other direction, as shown in
Figure 2.9
for a water depth higher
than 12 m, noting that the directions are rotated every 22.5
°
°
to define the eight
directions regardless of the platform
'
s orientation.
Comparison of Wind and Wave Calculations
Calculation of the force affecting the structure due to wind takes the drag
force into consideration and neglects the inertia force, but in the case of
waves, drag force and inertia force are considered in the calculation. The fol-
lowing example demonstrates the reason for neglecting the inertia force in
wind load.
If the platform is oriented as shown in
Figure 2.9
, so that the direction of wind
is not perpendicular to the faces of the platform, during calculation of the wind
N
0.85
Wave direction
clockwise from N
0.95
Factor
335
20
0.70
1.00
65
290
110
0.70
245
155
200
0.90
0.70
0.75
FIGURE 2.9
The design shows wave directions and factors to apply to the omnidirectional wave
height in the GoM.
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