. The elevation and duration of wave crests. Water waves. linearly superimposed to determine the generator blade motion. Figure 7 shows a sample of observed and predicted wave spectra. 18,67 '^ - - - Predicted Wave Spectrum 0 Observed Wave Spectrum Frequency ( Hz ) Figure 7. Observed and predicted wave spectra (sample of Pierson-Moskowitz spectra). In all tests the water surface time history was recorded at each wave gage for 4,096 data points. A sampling rate of 16 times per second was used for waves with periods less than 3
. The elevation and duration of wave crests. Water waves. linearly superimposed to determine the generator blade motion. Figure 7 shows a sample of observed and predicted wave spectra. 18,67 '^ - - - Predicted Wave Spectrum 0 Observed Wave Spectrum Frequency ( Hz ) Figure 7. Observed and predicted wave spectra (sample of Pierson-Moskowitz spectra). In all tests the water surface time history was recorded at each wave gage for 4,096 data points. A sampling rate of 16 times per second was used for waves with periods less than 3 seconds, and a rate of 8 times per second was used for waves with periods greater than 3 seconds. The data were digitized and recorded on magnetic tape through the use of a Data Acquisition System (DAS). An analysis of the tapes was performed later on a general-purpose computer. Two distinct types of data analysis were performed on the digitized wave records: a fast Fourier transform (FFT) and a zero up-crossing analysis. The FFT was used to determine the spectrum of the wave record, such as shown in Figure 7, which in turn was. used to deterraine the period of peak energy density. The period of peak energy density, Tp, is the reciprocal of the frequency of the midpoint of the 11 consecutive spectral lines with the most wave energy. The zero up-crossing method of analysis is used to determine the wave heights, crest heights, wave periods, and crest durations of individual waves in irregular wave trains or average values for monochromatic wave trains. Crest height. is measured relative to the mean water level (MWL) and. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Seelig, William N; Ahrens, John; Grosskopf, William G; Coastal Engineering Research Center (U. S. ). Fort Belvoir, Va. : U. S. Army, Corps of E
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