positions for a period of 10 sec to accurately measure the wave board
displacement.
These calibration measurements are entered into program WMCAL, an
acronym for Wave Machine Calibration, which produces a wave machine
calibration file. The calibration drive signal includes an extra 2-sec pause at
50 percent of full forward stroke. This pause is used to verify the polarity of the
drive signals. If this extra pause occurs on the reverse stroke of the wave board
instead of the forward stroke, the wave machine has reverse polarity. In this
case, RWREP5 multiplies the drive signal by -1 so that the generated waves will
have correct polarity and phase. After the static calibration is complete, all of the
control parameters related to each particular wave machine can be obtained
directly from the calibration file.
GEDAP also includes a method of dynamically calibrating the wave
generators to compensate for the magnitude and phase lag of the wave boards at
higher frequencies. This procedure was carried out initially, however, the results
proved that the servo-electric drive systems of the four wave generators in the
LSTF have very minimal magnitude and phase lag at higher frequencies.
Therefore, only the static calibration procedure described above is required.
Synthesis of regular wave drive signals
A GEDAP batch file named REGULAR_WAVE_SYNTHESIS has been
developed to synthesize regular wave drive signals. This batch file runs the
program RWREP5, which includes the regular wave generation options: (a) the
user specifies the wave height and the wave period; (b) the user specifies the
wave height, and the program calculates the corresponding period for a wave of
maximum steepness based on the breaking wave limit; and (c) the user specifies
the wave period, and the program calculates the corresponding height for a wave
of maximum steepness based on the breaking wave limit. Option a is normally
used for experiments in the LSTF. The program RWREP5 obtains calibration
information for each wave generator from the four wave machine calibration files
created using the program WMCAL. Four drive signal files are output from the
program RWREP5, one to drive each of the wave generators.
Synthesis of irregular wave drive signals
A GEDAP batch file named IRREGULAR_WAVE_SYNTHESIS was
developed to synthesize irregular wave machine drive signals. The general
procedure consists of the following steps. First, the program PARSPEC, an
acronym for Parametric Spectra, is used to synthesize a wave energy spectrum
using one of the theoretical parametric models. The option for a Texel, Marsen,
and Assloe (TMA) shallow water spectrum is normally used in the LSTF.
Several input parameters need to be defined, including the water depth at the
wave generators, the frequency of the wave spectrum peak, the peakedness factor
of the spectrum, and the significant wave height.
65
Chapter 7
Wave Generation and Current Recirculation
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