ssc-367 - Ship Structure Committee

The wave height exceedance diagram is a curve showing the percentage
of the wave records for which the significant wave height was greater
that the particular height.
M
WAVE SCATTER DIAGRAM
Wave scatter diagrams show the occurances of combinations of
significant wave height and average zero-uncrossing period over an
extended time period such as many years.
Wave height distribution over time can be obtained by actual wave
measurements. The heights and periods of all waves in a given
direction are observed for short periods of time at regular
intervals. A short time interval of several hours may be considered
constant. For this sea state, defined as “stationary”,the mean zero
up-crossing period, Tz, and the significant wave height, Hs, are
calculated. The Hs and Tz pairs are ordered and their probabilities
of occurance written in a matrix form, called a wave scatter diagram.
Sometimes wave scatter diagrams are available for the sea and for the
swell. The sea scatter diagram includes the sea spectra generated
locally. The swell scatter diagram contains the swell spectra (or
regular waves) generated far from the area, days before. Due to
greater energy losses in high frequency waves and the continual phase
shifting caused by viscosity, the energy in irregular seas tends to
shift toward longer periods, and the spectra becomes more peaked as
time passes. The energy in the swell is concentrated about a single
long period/low frequency, and often the swell is treated as a single
regular wave.
A typical wave scatter diagram, presenting statistical data on the
occurance of significant wave height and zero up-crossing period per
wave direction is shown on Figure A-2.
A-19