APPENDIX A: DESCRIPTION OF WAVE ANALYSIS 



Data Acquisition and Analysis 



1. Wave gages in the physical model were calibrated prior to collecting data. This was done by moving 

 gage sensor rods through a series of vertical steps to obtain calibration coefficients from a least-squares 

 linear or quadratic fit of the voltage versus submerged gage position. The US Army Engineer Waterways 

 Experiment Station (WES) process IDCAL ensures that proper gage potentiometer coefficients are used, 

 and it also generates descriptive information for documenting and archiving test output and data files. 

 Wave data were collected in real-time, with a sampling rate of 20 Hz. Data acquisition and the wave board 

 are driven by another WES process labeled SPLASH2. To assure smooth transition of the wave board 

 between successive points, the command signal rate was set at 20 Hz. 



2. Prior to data analysis, the calibration coefficients and header information created by the process 

 IDCAL are combined with the water surface elevation data collected by process SPLASH2 and converted 

 to engineering units for analysis by the WES process Time Series Analysis File (TSAF). Program TSAF is 

 designed such that a user-defined process control file can be used to select which types of analysis to 

 perform on the data. Among the analyses available in TSAF are single channel frequency analysis, multiple 

 channel upcrossing analysis, multiple channel downcrossing analysis, and Goda analysis. The process 

 control file contains information regarding how much of a particular data record to analyze, which channels 

 are to be used in the data analysis, plotting instructions, whether or not to save certain values, and several 

 other options. Hard copy output from TSAF can be in the form of printouts of parameters chosen, 

 frequency plots, and strip charts as discussed below. 



Time Series Analysis File (TSAF) 



3. The following description of the TSAF package is abstracted from Briggs^ and the TSAF package 

 itself. Readers desiring more complete descriptions of the processes mentioned here should consult these 

 references. In the TSAF code, the program reads and performs both time and frequency domain analysis 

 on the collected water surface elevation data. In these analyses, the code assumes that the water surface 



^Brig^, M. J. 1988. "Unidirectional Spectral Wave Generation and Analysis in Wave Basins," Volume I, Technical Report 

 CERC-88-11, US Army Engineer Waterways Experiment Station, Vicksburg, MS 



Al 



