Sea state Flashcards
Beaufort Scale
0: calm
1: light air
2: light breeze
3: gentle breeze
4: moderate breeze
5: fresh breeze
6: strong breeze
7: near gale
8: gale
9: strong / severe gale
10: storm
11: violent storm
12: hurricane force
regular sea state
H= const. and T= const.
natural sea state
H= variable and T= variable
aspects of sea state parameterisation
time domain and frequency domain
definition of a wave (zero-crossing-method):
Event between two successive passages of the water level oscillation through the meanwater level (oscillation centerline) in the same direction (up/down)
Classification of Wave Spectra
- Deep Water Wave Spectra
-well-developed and
decades of experience
(oceanography):
i.a. PM & JONSWAP spectrum - „Shallow Water“ Wave Spectra
-relatively new field of research
and less experiences
(coastal engineering):
Fourier-transformation
transformation of wave forms into a spectrum of amplitude and phase
inverse fourier-transformation
transformation of spectrum back into wave form
Hm
mean wave height of all recorded waves
Hm=sum(Hi)/N
H1/3
mean wave height of top 33% of highest waves
=> H1/10 = mean wave height of top 10% of highest waves etc
Hrms
Height of root mean square:
Hrms=sqrt(sum(Hi^2)/N)
Tm
Mean wave period of all recorded waves
Tm= sum(Ti)/N
T(H1/3)
mean wave period of the 33% highest waves
T1/3
Mean wave period of the 33% longest waves
Hmax
maximum wave height:
Hmax= sqrt(ln(N)/2)*Hs
Hs=H1/3
S(fi)
S(fi)=a,i^2(f)/(2*df)
Hm,0
Hm,0=4*sqrt(m0)
m0= integral(S(f))*df
Tm0,1
Tm0,1=m0/m1
mi=sum(S(fi)fidfi)
eta(t)
eta(t)=sum(eta,i)
eta,i=a,icos(omega,it+phi,i)
TMA-Spektrum, JONSWAP, PM-Spektrum
TMA-Spektrum: shallow water spectrum, not fully developed sea state, Nearly constant water depth
JONSWAP: deep water spectrum, not fully developed sea state, north sea, 2 parameter spectrum
PM-Spektrum: deep water spectrum, fully developed sea state, too high wave periods
