Practical Ship Hydrodynamics

114 Practical Ship Hydrodynamics
Table 4.1 Sea spectra for various wind duration times for Uc = 20 m=s
Quantity Case 1 Case 2 Case 3
Assumed wind duration time t (h) 5 20 50
Non-dimensial duration time 8 830 35 000 88 000
Maturity parameter Uc/cp 2.24 1.24 1
Significant wave higher H1/3(m) 2.26 6.00 8.56
ωp D g/cp D g/Uc Ð Uc/cp ⊲s 1 ⊳ 1.10 0.61 0.49
Modal period 2 /ωp (s) 5.7 10.3 12.8
s (w) (m 2 s)
12
10
8
6
4
320
1000 km
w (s−1 2
100
0
32
0.4 0.6 0.8 1.0 1.2 1.4 1.6
)
Figure 4.12 Wind sea spectra for uc D 20 m/s for various fetch values
H 1/3 (m)
20
15
10
5
0
0
5
5
Windsea
Swell
2.5
2.0
1.5
1.2
1.0
U c /c p =
10 15 20
10 15 20 25 30
cp (m/s)
T p (s)
Figure 4.13 Correlation between significant wave height H1/3, modal period Tp, wind speed
Uc and wave celerity at modal frequency cp