EM 1110-2-1100 (Part II)
30 Apr 02
Figure II-1-26. Definition of wave parameters for a random sea state
Figure II-1-27. Definition sketch of a random wave process (Ochi 1973)
are present. The monochromatic wave theories described in the first part of this chapter will be seen to have
two major uses. One use is to estimate the kinematics and dynamics associated with a wave with the
significant wave height, peak period, and direction. The other is when an individual wave has been isolated
in a wave record to estimate the velocities, accelerations, forces, etc., associated with that individual wave
event. The engineer must recognize that the implication of the statistical nature of irregular waves implies
that the kinematics and dynamics likewise require statistical treatment. IAHR (1986) provides a detailed
description of parameters and terminology used with irregular waves.
(6) Two approaches exist for treating irregular waves: spectral methods and wave-by-wave (wave train)
analysis. Spectral approaches are based on the Fourier Transform of the sea surface. Indeed this is currently
the most mathematically appropriate approach for analyzing a time-dependent, three-dimensional sea surface
record. Unfortunately, it is exceedingly complex and at present few measurements are available that could
fully tap the potential of this method. However, simplified forms of this approach have been proven to be
very useful. The other approach used is wave-by-wave analysis. In this analysis method, a time-history of
II-1-64
Water Wave Mechanics
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