7.6. IRREGULAR (2-D) WAVE GENERATION
395
cess could conceivably result in irregular wave conditions
that are unrealistic in terms of natural sea states.
Reproduction of measured sea surface elevation time series is not included
in this discussion of synthesized irregular waves; but in terms of the above
definitions, reproducing measured irregular waves is most certainly deterministic.
Arguments favoring the nondeterministic, partially deterministic, and
deterministic methods for irregular wave synthesis were summarized by
Funke and Mansard (1987) and Huntington (1987). Other authors have
also expressed opinions on the strengths and weaknesses of the various
synthesis methods, and several of these arguments will be mentioned in the
following sections.
Nondeterministic Irregular Wave Synthesis
As mentioned, a standard first-order model of a random sea state assumes
a stationary, ergodic random process with sea surface elevations exhibiting
a Gaussian distribution (Huntington 1987, Miles and Funke 1988). We also
assume the energy contained in the random sea can be characterized by a
spectrum in the frequency domain.
Huntington (1987) noted that a well constructed synthetic irregular
wave train should contain the statistical variability representative of naturally occurring waves, meaning the probability of occurrence of a specified
sea surface elevation (in two-dimensions) should be the same as the probability that occurs for a point measurement (nondirectional) in the ocean.
Achieving similar statistical variability in laboratory waves is the goal of
the nondeterministic approach to irregular wave synthesis.
One problem with the nondeterministic approach is that lengthy time
series realizations must be produced in order to assure a good statistical
representation in the irregular wave time series. In physical model simulations lengthy runs are costly and give rise to enhanced laboratory effects,
such as seiching in the flume. Huntington (1987) acknowledged the conflict
caused by the desire to represent correctly the statistical variability of the
irregular wave condition with lengthy run times versus the desire to keep
test runs short because of costs. But he argued for the nondeterministic
method because it most closely approximates real waves, and the longer
tests are sometimes needed to understand some of the more sophisticated
nonlinear responses present in some coastal and ocean engineering problems.
Another argument in support of lengthy runs of irregular waves synthesized by nondeterministic methods was given by Funke and Mansard
395
cess could conceivably result in irregular wave conditions
that are unrealistic in terms of natural sea states.
Reproduction of measured sea surface elevation time series is not included
in this discussion of synthesized irregular waves; but in terms of the above
definitions, reproducing measured irregular waves is most certainly deterministic.
Arguments favoring the nondeterministic, partially deterministic, and
deterministic methods for irregular wave synthesis were summarized by
Funke and Mansard (1987) and Huntington (1987). Other authors have
also expressed opinions on the strengths and weaknesses of the various
synthesis methods, and several of these arguments will be mentioned in the
following sections.
Nondeterministic Irregular Wave Synthesis
As mentioned, a standard first-order model of a random sea state assumes
a stationary, ergodic random process with sea surface elevations exhibiting
a Gaussian distribution (Huntington 1987, Miles and Funke 1988). We also
assume the energy contained in the random sea can be characterized by a
spectrum in the frequency domain.
Huntington (1987) noted that a well constructed synthetic irregular
wave train should contain the statistical variability representative of naturally occurring waves, meaning the probability of occurrence of a specified
sea surface elevation (in two-dimensions) should be the same as the probability that occurs for a point measurement (nondirectional) in the ocean.
Achieving similar statistical variability in laboratory waves is the goal of
the nondeterministic approach to irregular wave synthesis.
One problem with the nondeterministic approach is that lengthy time
series realizations must be produced in order to assure a good statistical
representation in the irregular wave time series. In physical model simulations lengthy runs are costly and give rise to enhanced laboratory effects,
such as seiching in the flume. Huntington (1987) acknowledged the conflict
caused by the desire to represent correctly the statistical variability of the
irregular wave condition with lengthy run times versus the desire to keep
test runs short because of costs. But he argued for the nondeterministic
method because it most closely approximates real waves, and the longer
tests are sometimes needed to understand some of the more sophisticated
nonlinear responses present in some coastal and ocean engineering problems.
Another argument in support of lengthy runs of irregular waves synthesized by nondeterministic methods was given by Funke and Mansard