2.1 Representative sea condition
2.1.1 The representative sea condition for all ships is
Beaufort 6, listed in table 2.1.
Table 2.1 Representative sea
condition for all ships
|
|
Mean wind
speed
Uwind
(m/s)
|
Mean wind
direction
γ (deg)
|
Significant wave
height
H (m)
|
Mean wave
period
T (s)
|
Mean wave
direction
θ (deg)
|
| BF6
|
12.6
|
0
|
3.0
|
6.7
|
0
|
2.1.2 The direction of wind and waves are defined as
heading direction, which has the most significant effect on the speed reduction.
2.2 Wind condition
2.2.1 The mean wind speed and wind direction are given in
table 2.1.
2.3 Wave condition
2.3.1 Symbols
- D : Angular distribution function
- E : Directional spectrum
- H : Significant wave height
- S : Frequency spectrum
- T : Mean wave period
- α : Angle between ship course and regular waves (angle 0(deg.) is defined as
the head waves direction)
- θ : Mean wave direction (θ = 0 (deg.))
- ω : Circular frequency of incident regular waves
2.3.2 As ocean waves are characterized as irregular ones,
the directional spectrum should be considered.
2.3.3 The significant wave height, mean wave period and
mean wave direction are given in table 2.1. To obtain the mean wave period from the
Beaufort scale, the following formula derived from a frequency spectrum for
fully-developed wind waves is used.
where, H is the significant wave height in metres and T is the mean wave
period in seconds.
2.3.4 The directional spectrum ( E ) is composed of
frequency spectrum ( S ) and angular distribution function ( D ).
where,