UFC 4-159-03
3 October 2005
Static Wind Yaw Moment. The static wind yaw moment is defined as the
4-4.3
product of the associated transverse wind force and its distance from the vessel's
center of gravity. In the local ship coordinate system, this is the moment about the "Z"
axis. Wind yaw moment is determined from the equation:
M xyw = 0.5 ρa Vw 2 A y LCxyw {θw }
(8)
EQUATION:
where
wind yaw moment (newton*m)
M xyw =
ρa =
mass density of air (from Table 4-1)
wind speed (m/s)
Vw =
longitudinal projected area of the ship (m2)
Ay =
length of ship (m)
L=
C xyw {θw } = normalized yaw moment coefficient
= moment arm divided by ship length
θw =
wind angle (degrees)
The normalized yaw moment coefficient depends upon the vessel type.
Equation 9 gives equations for computing the value of the yaw moment coefficient and
Table 4-5 gives empirical parameter values for selected vessel types. The normalized
yaw moment variables is found from:
θw * 180
EQUATION: Cxyw {θw } = - a1 * sin(
0<θw<θz
(9)
)
θz
Cxyw {θw } = a2 * sin[(θw - θz ) * λ )] θz≤θw<180 deg
(9a)
and symmetrical about the longitudinal axis of the vessel,
where
Cxyw {θw } =
normalized wind yaw moment coefficient
a1 =
negative peak value (from Table 4-5)
positive peak value (from Table 4-5)
a2 =
θw =
wind angle (degrees)
θz =
zero moment angle (degrees) (from Table 4-5)
180 * deg
λ =
(dimensionless)
(9b)
[
]
(180 * deg - θz )
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