PROPERTIES
OF WAVES
All waves have the following properties in
common:
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Amplitude.
The amplitude of a wave is the maximum vertical displacement of a particle
of the wave from its rest position. In the case of ocean waves, the
rest position is sea level.
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Wave
Height (H). Wave height is the vertical distance from the
top of the crest to the bottom of the trough. Wave height is measured in feet. Four values
for wave height are determined and forecast. They are:
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-
Havg
(the average height of the waves). This
average includes all the waves from the smallest ripple to the largest
wave.
-
Hsig
or H1/3
(the average height of the highest
one-third of all waves). This significant height of waves seems to
represent the wave heights better than the other values, and this value
will be used most often for this reason
-
H1/10
(the average height of the highest
one-tenth of all waves). H1/10
is
used to indicate the extreme roughness of the sea.
-
Hmax
- high wave.
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Period
(T). The period of a wave is the time interval between successive wave
crests, and it is measured in seconds.
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Frequency
(f). The frequency of waves is the number of waves passing a
given point during 1 second. It is the reciprocal of the period. In general, the
lower the frequency, the longer the wave period; the larger the frequency,
the shorter the wave period.
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Figure 6-2.-Swell waves.
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Wave
Length (L). The wave length is the horizontal distance
between two successive crests or from a point on one wave to the corresponding point on the
succeeding wave. Wave length is measured in feet, and it is found by the
formula:
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L
= 5.12 T 2
.
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Wave
Speed
(C). The wave speed is the rate that a particular phase of motion moves
along through the medium. It is the rate that a wave crest moves through the
water. There are two speeds used in ocean wave forecasting: group speed and
individual speed. The group speed of waves is approximately one-half that of
the individual speed The individual wave speed
in knots is found by the formula C = 3.03 T. The group wave speed is found
by the formula C = 1.515 T.
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