7.8. ADDITIONAL WAVE GENERATION TOPICS
445
wave boards, wave gauges might be more practical and convenient. Bullock
and Murton went on to describe in detail the design requirements of an
active absorbing wave board and its feedback and control systems. They
illustrated the principle of active absorption using a wedge-type wave board
situated in a short wave flume, and the effectiveness of the system was
demonstrated for both regular and irregular waves.
Yoshikawa and Chin (1989) described a three-dimensional absorbing
wave generator capable of producing continuous waves without contamination by the re-reflection of waves reflected by model structures or boundaries. Each of the wavemaker’s 40 wave board segments had a wave gauge
mounted on the front surface and a potentiometer to measure the wave
board segment displacement. Details on the theory and implementation
are given in Yoshikawa and Chin’s paper.
The design of an absorbing wave board must consider the range of wave
frequencies that need to be absorbed. As wavelength increases, more wave
board stroke is needed to damp the reflected wave. In addition, the designer
must allow for the possibility that the requirement of excess stroke to absorb
reflected waves will arise when the board is already well off its zero position.
Another consideration is that the feedback system will need safety controls
to prevent excessive wave board accelerations or displacements that might
damage the wavemaker.
7.8.3 Other Types of Wavemakers
The one feature shared by all of the wavemakers discussed in this chapter has been the stipulation of a solid, impervious wave board. Although
solid wave boards are far and away the most common, theories have been
developed for several nonconventional methods for generating waves in laboratory facilities.
An English translation (Simons and Devimeux 1966) of an original 1956
article that first appeared in Revue Générale de 1’Hydraulique presented a
theory for a wavemaker referred to as a “compound wave machine with
flexible elements.” This type of wavemaker consists of a conventional solid
flap-type wave board with a set of flexible elements extending over the depth
and spaced in an array in front of the wave board. The flexible sheets
(e.g., burlap, plastic, flexible sheet metal) are suspended vertically and
weighted at the bottom. Waves are generated by the wave board, and the
oscillatory motion is transmitted by each flexible sheet with the final sheet
representing the actual wave generator. This arrangement was reporte y
capable of absorbing reflected waves and it could generate second
waves without free higher harmonics.
.
Keulegan (1966) published approximate theories for generation of ong
445
wave boards, wave gauges might be more practical and convenient. Bullock
and Murton went on to describe in detail the design requirements of an
active absorbing wave board and its feedback and control systems. They
illustrated the principle of active absorption using a wedge-type wave board
situated in a short wave flume, and the effectiveness of the system was
demonstrated for both regular and irregular waves.
Yoshikawa and Chin (1989) described a three-dimensional absorbing
wave generator capable of producing continuous waves without contamination by the re-reflection of waves reflected by model structures or boundaries. Each of the wavemaker’s 40 wave board segments had a wave gauge
mounted on the front surface and a potentiometer to measure the wave
board segment displacement. Details on the theory and implementation
are given in Yoshikawa and Chin’s paper.
The design of an absorbing wave board must consider the range of wave
frequencies that need to be absorbed. As wavelength increases, more wave
board stroke is needed to damp the reflected wave. In addition, the designer
must allow for the possibility that the requirement of excess stroke to absorb
reflected waves will arise when the board is already well off its zero position.
Another consideration is that the feedback system will need safety controls
to prevent excessive wave board accelerations or displacements that might
damage the wavemaker.
7.8.3 Other Types of Wavemakers
The one feature shared by all of the wavemakers discussed in this chapter has been the stipulation of a solid, impervious wave board. Although
solid wave boards are far and away the most common, theories have been
developed for several nonconventional methods for generating waves in laboratory facilities.
An English translation (Simons and Devimeux 1966) of an original 1956
article that first appeared in Revue Générale de 1’Hydraulique presented a
theory for a wavemaker referred to as a “compound wave machine with
flexible elements.” This type of wavemaker consists of a conventional solid
flap-type wave board with a set of flexible elements extending over the depth
and spaced in an array in front of the wave board. The flexible sheets
(e.g., burlap, plastic, flexible sheet metal) are suspended vertically and
weighted at the bottom. Waves are generated by the wave board, and the
oscillatory motion is transmitted by each flexible sheet with the final sheet
representing the actual wave generator. This arrangement was reporte y
capable of absorbing reflected waves and it could generate second
waves without free higher harmonics.
.
Keulegan (1966) published approximate theories for generation of ong