ssc-367 - Ship Structure Committee

[dn/dx]max= aW2/g .
Squaring the equation to
get the slope squared,
[dn/dx]2 = a2*(~4/g2)
Therefore, the wave spectrum equation must be multiplied by (~4/g2)
to obtain the slope spectrum. The wave slope angle spectrum is the
wave slope spectrum converted to degrees squared, i.e., multiplied by
(180/r)2.
B.2.3.2 Wave Spectra for Moving Vessels
For self-propelled vessels or structures under tow, the forward speed
of the vessel or structure will have an effect upon the apparent
frequency of the waves. The apparent frequency of the waves is
usually referred to as the encounter frequency. For a vessel heading
into the waves the encounter frequency is higher than the wave
frequency seen by a stationary structure. For a vessel moving in the
same direction as the waves, the encounter frequency is less than the
wave frequency seen by a fixed structure, and if the vessel’s speed
is great enough it may be overrunning some of the shorter waves which
will give the appearance that these shorter waves are coming from
ahead instead of from behind.
The encounter frequency for a regular wave is given by the following
relationship.
‘e = u + VuZ/g
where u is the wave frequen~y in radians per second as seen
from a stationary observer,
v is the
velocity component parallel to and opposite in
direction to the wave direction, and
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