ssc-367 - Ship Structure Committee

A. REVIEH OF OCEANENVIRONMENT
The ocean environment is characterized by waves, wind and current.
The waves are typically irregular (confused or random seas). Some
waves are generated locally by the wind, and some waves are generated
great distances away. The wind is unsteady, with gusts. The wind
varies with height above water. The current is caused by the wind,
by waves, by the tide, and by global temperature differences. The
current varies with depth. All of these characteristics vary with
time.
A.1 IRREGULARWAVES
Irregular waves (a random sea) can be described as the sum of an
infinite number of individual regular (sinusoidal)waves of different
amplitude, frequency, and phase (Figure A-l). Therefore, the
randomly varying sea surface elevation can be represented by a
Fourier series.
N
n(t) = z
i=l
a*cos(wi*t+Oi) i
—
where n(t) is the water surface elevation measured from
still water level,
ai
is the amplitude of each component regular wave,
w. is the frequency of each component regular wave,
1
$j is the phase ang’ e of each component regular
wave, and
t
is time.
A-1
,/-—,
w!