Environmental Engineering Reference
In-Depth Information
approximation for very large values of n.
Ref. [11] contains the following values for the design wave:
2)
- Characteristic value of design wave period:
q
H
s
;
50
=
q
H
s
;
50
=
11
:
1
g
T
D
14
:
3
g
25 s
where H
s,50
is the significant wave height for a 50-year return period
- Characteristic value of design wave height:
p
0
H
D
¼
H
max
;
50
¼
H
s
;
50
:
5
ln T
ref
=
ð
T
D
Þ
where T
ref
is the 3 h reference period (
¼
3
60
60
¼
10 800 s)
The distribution function (Weibull or Gumbel) can be used as an alternative. The
smaller value governs.
Accordingly, the value for the aforementioned example is
p
16
11
:
1
:
06
=
9
:
81
¼
11
:
1
1
:
28
¼
14
:
2s
T
D
14
:
3
1
:
28
¼
18
:
3s
25 s
T
ref
T
D
j
mean
¼
10 800
2
¼ 665
ð
14
:
2 þ 18
:
3
Þ=
p
ln 66ð =
a
H
n¼665
H
D
¼
¼ H
s;50
2
¼ 16
:
06 1
:
80 ¼ 29
:
0m
2.5.9 Breaking waves
The height of breaking waves depends on the depth of water and the slope of the seabed.
Basically, it is not necessary to consider any wave heights higher than those of breaking
waves (see [11] 4.2.3.1.5).
In a limited depth of water, the wave kinematics can change considerably with respect
to the deep-water conditions. Wave crests are much higher and shorter than wave
troughs, and the wave profile is asymmetric in such a way that the front flank of the
wave crest is steeper than its rear flank. In addition, the distribution function for the
wave heights no longer corresponds to a Rayleigh distribution.
In shallow water (index “sh”) the empirical limit to the wave height (H
lim
)is
H
lim
;
sh
0
:
78
d
where d is the local depth of water.
However, waves can break in deep water (index “dp”) as well, with a theoretical
steepness of 1/7 related to the wavelength (
l
):
H
lim
;
dp
1
=
7
l
2)
The “design” values are characteristic values in the context of the safety concept!
