Page 70
Aanderaa Data Instruments AS – TD302
Mean Wave Period:
The Mean Wave Period is defined as:
0
01
1
( )
( )
i
i
m
i
i
i
S f
m
T
m
f S f
=
=
∑
∑
From this equation it can be seen that the mean wave period,
01
m
T
, is the inverse of the weighted average frequency
of the spectrum and hence a measure of the average period of the wave motion. Refer NOTE on page 71.
Energy Wave Period:
The Energy Wave Period is defined as:
1
10
0
m
m
T
m
−
−
=
The Energy Wave period is used in calculations of the wave power in [kW/m] of wave fronts. The wave power is
given as:
10
2
0
49
.
0
−
⋅
⋅
=
m
m
T
H
J
Refer NOTE on page 71.
Regularity:
When studying the wave parameters provided e.g. by the WTS, note that the motion of the sea surface caused by
the waves is a random process.
Significant wave height is for example a measure of the average wave height. The height of many, if not most, of the
waves in a record will differ from the significant wave height. The more irregular the sea state, the broader the wave
spectrum. A measure of the peakedness of the spectrum, and correspondingly of the regularity of the sea is:
2
2
2
2
0
0
0
0
2
2
( )
( )
N
p
i
i
Q
f S
f df
f S
f
m
m
∞
=
⋅
≈
⋅
∑
∫
Generally, a calm sea gives a narrow/peaked spectrum and a high
p
Q
factor; an irregular sea will give a broader
spectrum and a lower
p
Q
value.
