406
CHAPTER 7. LABORATORY WAVE GENERATION
state in physical models (which produce continuous realizations), and they
listed the following realities of physical model wave generation that might
cause deviation between the numerical and physical model simulations:
• Lack of understanding about the transfer function characteristics of the hydraulic servo-system, which can change
with water depth or suffer severe pressure loss due to inadequate pump capacity
• Reflections from boundaries and wave absorbers
• Linear and nonlinear distortions caused by a rigid wave
board
• Wave-wave interactions transferring wave energy into adjacent frequencies during propagation
• Resonance of water behind the wave board or loss of water
through gaps between the wave board and side walls and
bottom, causing a loss of low-frequency energy
• Recirculating currents within the wave facility
Because of the above-listed influences, an iterative technique was developed that allows an empirical correction to the wave board spectrum so
that it more closely matches the target spectrum. Generally, the following
steps are followed:
1. Select and scale the target spectrum for physical model
reproduction.
2. Convert the target spectrum to a wave board spectrum using the first-order transfer function, and synthesize a wave
board time displacement time series.
3. Generate the wave condition in the test facility, and measure the waves at the desired locations. The measured time
series are then converted to wave spectra and compared
with the target spectrum.
4. Determine a frequency domain transfer function, defined
as
TrnM =
[‘$nr)(u,n)]target
((^n )] measured
(7.197)
and apply this transfer function to the wave board spectrum.
CHAPTER 7. LABORATORY WAVE GENERATION
state in physical models (which produce continuous realizations), and they
listed the following realities of physical model wave generation that might
cause deviation between the numerical and physical model simulations:
• Lack of understanding about the transfer function characteristics of the hydraulic servo-system, which can change
with water depth or suffer severe pressure loss due to inadequate pump capacity
• Reflections from boundaries and wave absorbers
• Linear and nonlinear distortions caused by a rigid wave
board
• Wave-wave interactions transferring wave energy into adjacent frequencies during propagation
• Resonance of water behind the wave board or loss of water
through gaps between the wave board and side walls and
bottom, causing a loss of low-frequency energy
• Recirculating currents within the wave facility
Because of the above-listed influences, an iterative technique was developed that allows an empirical correction to the wave board spectrum so
that it more closely matches the target spectrum. Generally, the following
steps are followed:
1. Select and scale the target spectrum for physical model
reproduction.
2. Convert the target spectrum to a wave board spectrum using the first-order transfer function, and synthesize a wave
board time displacement time series.
3. Generate the wave condition in the test facility, and measure the waves at the desired locations. The measured time
series are then converted to wave spectra and compared
with the target spectrum.
4. Determine a frequency domain transfer function, defined
as
TrnM =
[‘$nr)(u,n)]target
((^n )] measured
(7.197)
and apply this transfer function to the wave board spectrum.