and Data Analysis
This chapter provides information on the data collection procedure and
analysis. Selected example plots of data are also shown.
Data Sampling and Wave Generation
Following daily calibration of the wave gauges (Chapter 2), and incident
wave conditions, the experiments began and both current and wave data were
collected. The wave generator was operated for 420 sec with a 10-sec ramp-up
and ramp-down time. The wave gauge sampling rate was 20 Hz, so 20,400 water
elevation data points were collected at each gauge, and 10,200 additional velocity
data samples (initially a 10-Hz sampling rate, but increased to 20 Hz early in the
study) for each sensor were collected during a run.
All spectral wave tests were made with a unidirectional JONSWAP wave
spectrum using the following spectral parameters:
a. For the tests with a target wave height Hs of 6.1 cm and peak wave
period Tp of 0.8 sec, a wave generator signal was created using the peak
enhancement factor γ of 3.3, low and high peak decay frequencies σa of
0.07 and σb of 0.09, respectively, and Phillips constant α of 0.03198.
The low and high cutoff frequencies of the spectrum were set to the
frequencies having 3 and 97 percent of the total spectral variance. In
these tests, these were 0.998 Hz and 2.839 Hz, respectively.
b. For the tests with Hs of 4.6 cm and Tp of 1.6 sec, a wave generator signal
was created with γ of 3.3, σa of 0.07 and σb of 0.09, and α of 0.00108.
The low and high cut-off frequencies of the spectrum were set to the
frequencies having 3 and 97 percent of the total spectral variance. In
these tests, these were 0.4989 Hz and 1.4196 Hz, respectively.
Figure 13 shows an example comparison of target and measured spectra at a
wave gauge location in front of the wave generator. Figure 14 shows a snapshot
of water-surface variation at two gauges.
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Chapter 3 Measurement Procedures and Data Analysis