by reflection, wave instabilities, or tank oscillations. This wave 

 height (referred to as the generated wave height in Vols. I to VII) is 

 assumed to remain constant as long as the generator operates smoothly. 



Wave height variability is any deviation in wave height from H^. 

 This variability can be spatial (the wave height varies with position 

 along the tank (longitudinally) or across the tank (laterally)), or 

 temporal (wave height varies with time at any point) . 



The terms used in describing and calculating wave height variability 

 are defined below. Variation in wave reflection from the profile, which 

 is the major source of wave height variability, and other sources of wave 

 height variability are discussed in this section. 



1. Definitions of Terms. 



a. Operational Terms . The following terms were used in the measure- 

 ment and calculation of wave height variability parameters. 



(1) Wave reaord--a. strip-chart recording containing all the 

 water surface elevation measurements during a given run. Wave records 

 include recordings made with a stationary gage or a slowly moving gage. 



(2) Crest and trough elevations and positions --determined from 

 wave records using a digitizer, which produced a deck of punchcards 

 containing the (a) position (on the recording) and elevation of all wave 

 troughs, (b) position and elevation of all wave crests, and (c) position 

 of all tick marks relating chart paper position to stations along the 

 wave tank. 



(3) Computer programs WVHTCN and !WF2 1 C2--written to automate the 

 analysis of wave height variability data. 



(4) Local wave height (Ej^) --the difference in elevation between 

 a trough and the succeeding crest, with its position defined midway 

 between the two points (determined by the program WVHTCN) . 



(5) Average wave height (H^J --the average of all the local wave 

 heights in a record (determined by the program WVHTCN) . 



(6) Running average wave height (H m )--the average of all local 

 wave heights within a standing wavelength (one-half the generated wave- 

 length) of a point (calculated for each H£ by the program WVHTCN) . 



(7) Running average wave height deviation (D m ) --calculated by 

 subtracting H^ from each H m along the tank (plotted as a function of 

 tank position by the program WVHTCN) . 



(8) Amplitude of the running average deviation (A m ) --determined 

 by measuring the maximum deviations on the plot of D^j versus tank 

 position and averaging the absolute values of the maximum deviations. 



