400
CHAPTER 7. LABORATORY WAVE GENERATIO
board signal (see section entitled First-Order Irregular Wave Generation
and generated in a wave flume. Sea surface elevation measurements wei
obtained after the wave trains had stabilized (about 3 minutes from onsi
of wave action).
Funke, Mansard, and Dai (1988) reported that the two synthesis metl
ods gave compatible results which fell within the expected band of var
ability. Differences were noticeable only for short record lengths. At Ion
record lengths the two methods produced nearly identical results. Th
finding agreed with their earlier numerical comparison. They also pointe
out that waves in the wave tank underwent a certain amount of evolutio
during propagation which may have affected the spectral characteristic
Differences between the two methods were also attributed to wave nonlii
earities.
The study concluded that differences between the NSA and DSA metl
ods are small in terms of the statistical parameters examined. Funke, (
al. reported that differences found between two records selected at randoi
from within the same synthesis method were similar to differences show
between records synthesized by the different methods. They also briefly e>
amined second order effects that arise when using a linear transfer functio
between wave time series and wave board signal.
Other Irregular Wave Synthesis Methods. Other methods for syr
thesizing nondeterministic and partially deterministic realizations of rar
dom sea states are available, but detailed discussion of the various method
is beyond the intended scope of this chapter.
Miles and Funke (1988) conducted a numerical comparison of the follow
ing six nonharmonic methods and one harmonic method for synthesizin
pseudo-random Gaussian irregular wave time series realizations for the lai
oratory.
1. Equal Amplitude Component Superposition where
the frequency density varies with spectral amplitude so
that each of the discrete spectral components has the same
amplitude
2. Deterministic Spectral Amplitude Technique which
uses a random distribution of frequencies with spacing that
increases with frequency and phases that are randomly selected from an uniform distribution
3. Random Amplitude and Frequency Method which
is a variation of the NSA method in that frequency is divided into equal increments and each discrete frequency is
CHAPTER 7. LABORATORY WAVE GENERATIO
board signal (see section entitled First-Order Irregular Wave Generation
and generated in a wave flume. Sea surface elevation measurements wei
obtained after the wave trains had stabilized (about 3 minutes from onsi
of wave action).
Funke, Mansard, and Dai (1988) reported that the two synthesis metl
ods gave compatible results which fell within the expected band of var
ability. Differences were noticeable only for short record lengths. At Ion
record lengths the two methods produced nearly identical results. Th
finding agreed with their earlier numerical comparison. They also pointe
out that waves in the wave tank underwent a certain amount of evolutio
during propagation which may have affected the spectral characteristic
Differences between the two methods were also attributed to wave nonlii
earities.
The study concluded that differences between the NSA and DSA metl
ods are small in terms of the statistical parameters examined. Funke, (
al. reported that differences found between two records selected at randoi
from within the same synthesis method were similar to differences show
between records synthesized by the different methods. They also briefly e>
amined second order effects that arise when using a linear transfer functio
between wave time series and wave board signal.
Other Irregular Wave Synthesis Methods. Other methods for syr
thesizing nondeterministic and partially deterministic realizations of rar
dom sea states are available, but detailed discussion of the various method
is beyond the intended scope of this chapter.
Miles and Funke (1988) conducted a numerical comparison of the follow
ing six nonharmonic methods and one harmonic method for synthesizin
pseudo-random Gaussian irregular wave time series realizations for the lai
oratory.
1. Equal Amplitude Component Superposition where
the frequency density varies with spectral amplitude so
that each of the discrete spectral components has the same
amplitude
2. Deterministic Spectral Amplitude Technique which
uses a random distribution of frequencies with spacing that
increases with frequency and phases that are randomly selected from an uniform distribution
3. Random Amplitude and Frequency Method which
is a variation of the NSA method in that frequency is divided into equal increments and each discrete frequency is