7.6. IRREGULAR (2-D) WAVE GENERATION
401
randomly selected from an uniform distribution over the
increment
4. Nonrecursive White Noise Filtering which involves
the linear filtering of pseudo-random white noise in the
time domain
5. Wallingford Method which filters binary white noise
6. Autoregressive Moving Average Filter Method in
which a specially constructed moving filter is used to modify Gaussian white noise in the time domain so it has the
desired spectral characteristics
7. Non deterministic Spectral Amplitudes Method in
which all frequency components are harmonically related
and the synthesis method uses the inverse FFT
The first six methods are nonharmonic, whereas the seventh method is
harmonic. Miles and Funke (1988) gave appropriate literature references
for each of the above synthesis methods.
Two hundred irregular wave time series realizations were synthesized by
each of the seven methods, and the records were compared on the basis of
16 statistical wave parameters. Second-order bound long wave components
were also investigated.
Miles and Funke (1988) concluded that the spectrally nondeterministic
methods were necessary to produce short-term wave records with the variability that would be expected in nature. However, they also stated that
any discrete time domain wave record generated by the nonharmonic synthesis techniques can be approximated without significant residual error by
an equivalent harmonic time series produced using the inverse FFT method.
Finally, they noted that generation times for the harmonic FFT methods
were about 20 to 30 times faster than for the nonharmonic superposition
methods, and the resulting harmonic time series exhibited reasonable Gaussian statistics provided a large number of frequencies were used.
Deterministic Irregular Wave Synthesis
Deterministic irregular wave synthesis (by the definition followed here) attempts to exercise additional control over some characteristic of the irreg
ular wave train. Most often the deterministic methods manipulate wave
grouping characteristics, or create particular sequences of waves or extreme
waves thought to be critical to the project undergoing physical model testing.
Arguments in favor of deterministic irregular wave synthesis methods
cite the fact that “deterministic” experimental runs can be much shorter
401
randomly selected from an uniform distribution over the
increment
4. Nonrecursive White Noise Filtering which involves
the linear filtering of pseudo-random white noise in the
time domain
5. Wallingford Method which filters binary white noise
6. Autoregressive Moving Average Filter Method in
which a specially constructed moving filter is used to modify Gaussian white noise in the time domain so it has the
desired spectral characteristics
7. Non deterministic Spectral Amplitudes Method in
which all frequency components are harmonically related
and the synthesis method uses the inverse FFT
The first six methods are nonharmonic, whereas the seventh method is
harmonic. Miles and Funke (1988) gave appropriate literature references
for each of the above synthesis methods.
Two hundred irregular wave time series realizations were synthesized by
each of the seven methods, and the records were compared on the basis of
16 statistical wave parameters. Second-order bound long wave components
were also investigated.
Miles and Funke (1988) concluded that the spectrally nondeterministic
methods were necessary to produce short-term wave records with the variability that would be expected in nature. However, they also stated that
any discrete time domain wave record generated by the nonharmonic synthesis techniques can be approximated without significant residual error by
an equivalent harmonic time series produced using the inverse FFT method.
Finally, they noted that generation times for the harmonic FFT methods
were about 20 to 30 times faster than for the nonharmonic superposition
methods, and the resulting harmonic time series exhibited reasonable Gaussian statistics provided a large number of frequencies were used.
Deterministic Irregular Wave Synthesis
Deterministic irregular wave synthesis (by the definition followed here) attempts to exercise additional control over some characteristic of the irreg
ular wave train. Most often the deterministic methods manipulate wave
grouping characteristics, or create particular sequences of waves or extreme
waves thought to be critical to the project undergoing physical model testing.
Arguments in favor of deterministic irregular wave synthesis methods
cite the fact that “deterministic” experimental runs can be much shorter