ANALYSING THE WAVE SPECTRUM FOR THE PERSIAN GULF IN ...

صفحه 176
چهاردهمين كنفرانس ژئوفيزيك ايران
.
.
3.2. DISTRIBUTION AND RANGES
The range and average value of wave parameters of the data considered in the study is shown in
figure #3 to #5.
Figure 2. Variation of mean wave period with
significant wave height
Figure 3. Variation of peak wave period with
significant wave height
Figure 4- Variation of peak wave period with
mean wave period.
4. RESULTS, DISCUSSIONS AND CONCLUSIONS
4.1. DATA DISTRIBUTION AND RANGE
Sea state is generally defined using few parameters derived from the wave spectrum. Significant
wave height (H s ) and peak period (T p ) are the most commonly used parameters. Mean wave period
associated with high wave is usually obtained by assuming a significant wave steepness. In the
present case, waves with H s higher than 0.5m are only considered. It was found that T m02 varies
0.5
0.5
between 2.5H s
and 7H
s
(figure #3). While ISSC (1979) recommendation shows T m02 is in a range
0.5
0.5
of 2.6H s
and 3.9H
s
.The present study shows that T m02 beyond ISSC range. T p was found to be
0.5
0.5
between 3.2H s
and 12.5H
s
(figure #4). T p was found to be varying between the values estimated
using the equations given below (figure #5):
T
p
4.5T
m02
4.8,
T 9.15 3.95 0.55
2
p
T
m02 T
m02
.
And also it was obviated that the relation between peak wave period and mean wave period is:
T p 1.51 Tm
02
(2)
4.2. COMPARISONS BETWEEN MEASURED WAVE SPECTRUMS AND STANDARD
SPECTRUMS RESULTS
The measured wave spectrum has been compared with the aforementioned well-known spectrums.
The spectral peak period estimated by the Scott and JONSWAP (Hasselmann) was higher than the
measured peak value (sometimes they deviate too much). It was found that the Pierson-Moskowitz
spectrum can sometimes estimate the spectral peak value but in prediction of peak wave period and
frequency band it is not reliable due to independency of T p in their formulas. It was found that
although most of the spectra were with predominant single peak, lots of them have local maximums
in higher frequencies as well. Another phenomenon which can be seen in comparisons is that TMA
spectrum fits better in deeper stations than the shallow waters although, the whole trend is not
acceptable.
Generally, the comparisons showed that the measured wave spectrum is more close to JONSWAP
spectrum modified by Ochi than the other spectrums. Then it was attempted to justify the modified
JONSWAP spectrum formula mentioned in equation #3.
4
2
g
5 f
S( f ) exp
4 5 (2 ) f 4
f
p
0.07, f