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CHAPTER 7. LABORATORY WAVE GENERATION
7.6 Irregular (2-D) Wave Generation
7.6.1 Introduction
Most physical models of coastal engineering problems involve forces resulting from the motion of gravity waves. In nature these waves are highly
irregular and seldom exhibit anywhere near the uniformity of a sinusoidal
wave train. Therefore, when it is appropriate, we should attempt to generate laboratory waves that closely approximate naturally occurring wave
trains, and we should identify and attempt to minimize unnatural laboratory effects that could influence the experiment outcome.
One common concession coastal engineers have made in reproducing
natural waves is to represent the three-dimensional sea state as a twodimensional process with irregular waves propagating in only one direction
in a wave flume or basin. Although this is fundamentally incorrect, twodimensional irregular waves are more amenable to theoretical treatment,
thus they offer an interim step toward building greater understanding of
the complexities of three-dimensional sea states.
The availability of servo-controlled hydraulic rams for use in driving
wavemakers provided the ability to control the wave board using a command signal, and this led to the appearance of the first irregular wave
generators at ship testing basins in the 1960’s (Goda 1985). In the 1970’s
there was a rapid growth in the number of operational irregular wavemakers in hydraulic laboratories5. Webber and Christian (1974) described
design considerations involved in developing a low-cost programmable wave
generator for irregular waves, and they gave details of actual component
selection and wavemaker performance. Other hydraulic laboratories have
written similar descriptions of their wavemaker designs. (See Funke and
Mansard (1987) for a summary of the literature on mechanical aspects of
wavemaker design.)
5 Funke and Mansard (1987) provided an interesting history of irregular wave synthesis and generation in laboratory flumes and basins, along with a comprehensive list of
references.
A survey of random wave generation techniques conducted by Ploeg
and Funke (1980) gave coastal engineers a “snapshot” of the number of
irregular wave generators in service at the beginning of the 1980’s. Ploeg
and Funke received responses from 98 hydraulic laboratories and 44 ship
towing model facilities worldwide. Of the 83 hydraulic laboratories and 35
ship towing facilities with wave generating capability, a total of 110 flumes
and 57 basins with irregular wavemakers were reported. These numbers
have undoubtedly increased since the time of the survey. Ploeg and Funke s
(1980) survey covered practically all aspects of laboratory wave generation
CHAPTER 7. LABORATORY WAVE GENERATION
7.6 Irregular (2-D) Wave Generation
7.6.1 Introduction
Most physical models of coastal engineering problems involve forces resulting from the motion of gravity waves. In nature these waves are highly
irregular and seldom exhibit anywhere near the uniformity of a sinusoidal
wave train. Therefore, when it is appropriate, we should attempt to generate laboratory waves that closely approximate naturally occurring wave
trains, and we should identify and attempt to minimize unnatural laboratory effects that could influence the experiment outcome.
One common concession coastal engineers have made in reproducing
natural waves is to represent the three-dimensional sea state as a twodimensional process with irregular waves propagating in only one direction
in a wave flume or basin. Although this is fundamentally incorrect, twodimensional irregular waves are more amenable to theoretical treatment,
thus they offer an interim step toward building greater understanding of
the complexities of three-dimensional sea states.
The availability of servo-controlled hydraulic rams for use in driving
wavemakers provided the ability to control the wave board using a command signal, and this led to the appearance of the first irregular wave
generators at ship testing basins in the 1960’s (Goda 1985). In the 1970’s
there was a rapid growth in the number of operational irregular wavemakers in hydraulic laboratories5. Webber and Christian (1974) described
design considerations involved in developing a low-cost programmable wave
generator for irregular waves, and they gave details of actual component
selection and wavemaker performance. Other hydraulic laboratories have
written similar descriptions of their wavemaker designs. (See Funke and
Mansard (1987) for a summary of the literature on mechanical aspects of
wavemaker design.)
5 Funke and Mansard (1987) provided an interesting history of irregular wave synthesis and generation in laboratory flumes and basins, along with a comprehensive list of
references.
A survey of random wave generation techniques conducted by Ploeg
and Funke (1980) gave coastal engineers a “snapshot” of the number of
irregular wave generators in service at the beginning of the 1980’s. Ploeg
and Funke received responses from 98 hydraulic laboratories and 44 ship
towing model facilities worldwide. Of the 83 hydraulic laboratories and 35
ship towing facilities with wave generating capability, a total of 110 flumes
and 57 basins with irregular wavemakers were reported. These numbers
have undoubtedly increased since the time of the survey. Ploeg and Funke s
(1980) survey covered practically all aspects of laboratory wave generation