Civil Engineering Reference
In-Depth Information
In deep water along an open coastline, wind-generated current velocities at the
SWL may, if statistical data are not available, be taken as V
c,wind
(0) = k (U
1
hour,
10 m), where k =0.015
0.03 and (U
1
hour, 10 m) is the 1-hour sustained wind
speed at height 10 m above sea level.
The variation of current velocity over depth depends on the local oceano-
graphic climate, the vertical density distribution and the flow of water into or
out of the area. This may vary from season to season. Deepwater profiles
may be complex. Current direction can change 180
−
with depth. A current pro-
file for a location in the GoM is shown in API-RP2A (2007). API mentions that
the minimum speed is 0.31 km/hr (see
Figure 2.10
).
°
Current Profile
The recommended current profile given in ISO 19901-1 (2005) is:
1/7
z
+
d
U
c
ð
z
Þ =
U
cs
(2.22)
d
where U
c
(z) is the current speed at elevation z(z
0), U
cs
(z) is the surface
current speed at z =0,d is the still-water depth and z is the vertical coordinate
measured positively upward from the SWL.
≤
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
Velocity depth factor
FIGURE 2.10
Current profile.
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