7.6. IRREGULAR (2-D) WAVE GENERATION
419
long wave resulted in less maximum runup, and in practice, this could lead
to a more economical design.
On the other hand, Barthel, Mansard, and Funke (1983a) noted that
long wave suppression did not greatly impact the average and root-meansquare runup statistics. From this observation we might conjecture that
correct reproduction of second-order bound long waves is more important
for those processes that are sensitive to singular wave events (maximum
wave runup, overtopping, armor unit stability) and less important for processes that are typically related to mean wave parameters, such as macroscale sediment transport processes and beach profile development.
Practical Considerations of Second-Order Long-Wave Correction.
Although the concept of reducing spurious long wave energy in flume testing is desirable, there are several practical aspects to the suppression that
need to be considered by researchers in the context of their specific testing
program and facilities.
• Calculation of the wave board control signal for correct
reproduction of bound long waves requires substantially
more computation than the first-order irregular wavemaker
theory. Fortunately, the continued development of powerful computer workstations has helped to alleviate this
concern.
• Implementation of the spurious long wave correction procedure requires increased wave board stroke due to the
generation of longer wave components, and this stroke requirement increases dramatically as the generation water
depth decreases. Consequently, the range of maximum significant wave heights that can be generated in a specific
facility will be reduced. If it is possible, the best situation
is to generate waves in relatively deep water, then have
them shoal in the flume. The deep water waves require
less correction for spurious long waves, and this will help
minimize additional board stroke requirements.
• As noted by Ottesen Hansen, et al. (1980), bound long
waves (set-down) will be absorbed during the breaking process provided the slope is gentle and the waves are spilling
breakers. Conversely, if the waves approach a steep slope,
such cis on a coastal structure, the bound wave will be
reflected as a free long wave back toward the wave board.
Upon reaching the wave board, the free wave is re-reflected
back toward the shoreline, and at this point unwanted long
419
long wave resulted in less maximum runup, and in practice, this could lead
to a more economical design.
On the other hand, Barthel, Mansard, and Funke (1983a) noted that
long wave suppression did not greatly impact the average and root-meansquare runup statistics. From this observation we might conjecture that
correct reproduction of second-order bound long waves is more important
for those processes that are sensitive to singular wave events (maximum
wave runup, overtopping, armor unit stability) and less important for processes that are typically related to mean wave parameters, such as macroscale sediment transport processes and beach profile development.
Practical Considerations of Second-Order Long-Wave Correction.
Although the concept of reducing spurious long wave energy in flume testing is desirable, there are several practical aspects to the suppression that
need to be considered by researchers in the context of their specific testing
program and facilities.
• Calculation of the wave board control signal for correct
reproduction of bound long waves requires substantially
more computation than the first-order irregular wavemaker
theory. Fortunately, the continued development of powerful computer workstations has helped to alleviate this
concern.
• Implementation of the spurious long wave correction procedure requires increased wave board stroke due to the
generation of longer wave components, and this stroke requirement increases dramatically as the generation water
depth decreases. Consequently, the range of maximum significant wave heights that can be generated in a specific
facility will be reduced. If it is possible, the best situation
is to generate waves in relatively deep water, then have
them shoal in the flume. The deep water waves require
less correction for spurious long waves, and this will help
minimize additional board stroke requirements.
• As noted by Ottesen Hansen, et al. (1980), bound long
waves (set-down) will be absorbed during the breaking process provided the slope is gentle and the waves are spilling
breakers. Conversely, if the waves approach a steep slope,
such cis on a coastal structure, the bound wave will be
reflected as a free long wave back toward the wave board.
Upon reaching the wave board, the free wave is re-reflected
back toward the shoreline, and at this point unwanted long