UFC 4-159-03
3 October 2005
STATIC CURRENT FORCES/MOMENTS. Methods to determine static
4-5
current forces and moments on stationary moored vessels in the surge and sway
directions and yaw moment are presented in this section. These planar directions are
of primary importance in many mooring designs.
Static Transverse Current Force. The transverse current force is
4-5.1
defined as that component of force perpendicular to the vessel centerline. If a ship has
a large underkeel clearance, then water can freely flow under the keel, as shown in
Figure 4-8(a). If the underkeel clearance is small, as shown in Figure 4-8(b), then the
ship more effectively blocks current flow, and the transverse current force on the ship
increases. These effects are considered and the transverse current force is determined
from the equation:
Fyc = 0.5 ρ w Vc2 LwL T Cyc sinθ c
(10)
EQUATION:
where
= transverse current force (newtons)
Fyc
ρw
= mass density of water (from Table 4-1)
= current velocity (m/s)
Vc
= vessel waterline length (m)
L wL
= average vessel draft (m)
T
= transverse current force drag coefficient
C yc
θc
= current angle (degrees)
The transverse current force drag coefficient as formulated in Broadside
Current Forces on Moored Ships, Seelig et al. (1992) is shown in Figure 4-9. This drag
coefficient can be determined from:
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