7.8. ADDITIONAL WAVE GENERATION TOPICS
437
Finally, Suh and Dalrymple (1987) presented a second-order directional
wavemaker theory that included the first-order irregular waves and the
second-order wave-wave interactions. Equations were given to subtract out
the second-order free waves at the wave board, but practically speaking, this
would involve a significant computational effort. Suh and Dalrymple also
pointed out that wavemakers do not always follow theoretical predictions
due to finite wave board segment lengths and gaps between the segments,
and this would impact the effectiveness of the corrections.
7.8 Additional Wave Generation Topics
The following short sections briefly summarize several topics related to
laboratory wave generation. Details are omitted, but pertinent literature
references are included for those who which to explore the topics further.
7.8.1
Spiral Wavemakers
Dean and Dalrymple (1984) summarized first-order wavemaker solutions
for waves being generated by the oscillatory motion of a vertical cylinder
in a basin. Three types of cylinder motion were covered:
1. The cylinder moving similar to a piston- or flap-type wave
board in a fixed vertical plane.
2. The cylinder pulsating by expanding and contracting radially without any angular component to the motion. (In a
symmetrical basin this would create concentric waves.)
3. The cylinder moving in a small circular pattern, either
uniformly over the depth (analogous to piston-type wave
boards) or with the bottom remaining stationary (analogous to flap-type wave boards). This type of wavemaker
was called the spiral wavemaker by Dalrymple and Dean
(1972).
The spiral wavemaker has particular interest for coastal engineers because it creates waves with crests that spiral outward from the wavemaker.
In a circular basin with a sloping bottom having circular depth contours,
the spiral waves impinge the beach everywhere with the same approach angle. Therefore, the circular beach can represent an infinitely long straight
beach without the problem of end effects that occur in conventional wave
basins with oblique wave approach. This is an ideal situation for littoral
transport studies that use movable-beds or fixed-bed tracers.
437
Finally, Suh and Dalrymple (1987) presented a second-order directional
wavemaker theory that included the first-order irregular waves and the
second-order wave-wave interactions. Equations were given to subtract out
the second-order free waves at the wave board, but practically speaking, this
would involve a significant computational effort. Suh and Dalrymple also
pointed out that wavemakers do not always follow theoretical predictions
due to finite wave board segment lengths and gaps between the segments,
and this would impact the effectiveness of the corrections.
7.8 Additional Wave Generation Topics
The following short sections briefly summarize several topics related to
laboratory wave generation. Details are omitted, but pertinent literature
references are included for those who which to explore the topics further.
7.8.1
Spiral Wavemakers
Dean and Dalrymple (1984) summarized first-order wavemaker solutions
for waves being generated by the oscillatory motion of a vertical cylinder
in a basin. Three types of cylinder motion were covered:
1. The cylinder moving similar to a piston- or flap-type wave
board in a fixed vertical plane.
2. The cylinder pulsating by expanding and contracting radially without any angular component to the motion. (In a
symmetrical basin this would create concentric waves.)
3. The cylinder moving in a small circular pattern, either
uniformly over the depth (analogous to piston-type wave
boards) or with the bottom remaining stationary (analogous to flap-type wave boards). This type of wavemaker
was called the spiral wavemaker by Dalrymple and Dean
(1972).
The spiral wavemaker has particular interest for coastal engineers because it creates waves with crests that spiral outward from the wavemaker.
In a circular basin with a sloping bottom having circular depth contours,
the spiral waves impinge the beach everywhere with the same approach angle. Therefore, the circular beach can represent an infinitely long straight
beach without the problem of end effects that occur in conventional wave
basins with oblique wave approach. This is an ideal situation for littoral
transport studies that use movable-beds or fixed-bed tracers.