Davis and Zarnick 



100 



10 



.2 .3 <l .5 .6 .7 .8 .9 1.0 



Frequency in cycles per second 



Fig. 30 - Comparison of transient wave height spectra 

 measured during zero and forward speed runs with 

 Model 4889 



and the wave transforms of the latter measurement do not correlate well, for- 

 ward probe with after probe. The remaining sources of error in the wave height 

 transform estimate have obviously not been isolated by these tests. 



AREAS OF CONTINUING DEVELOPMENT EFFORT 



General 



The understanding and counteracting of the various factors leading to an in- 

 accurate wave height measurement will be undertaken as the major effort in de- 

 veloping further the capability of the transient wave test. A series of tests in 

 waves, with and without a model, is planned in order to investigate the error 

 contributions from (1) nonlinear water dynamics, (2) nonlinear measurement by 

 the wave height probe, (3) spatial variations in basin waves, (4) side or end re- 

 flections, (5) residual waves after passage of the main wave, (6) faulty Fourier 

 analysis, (7) electronic interaction between adjacent wave probes, and (8) model- 

 generated waves. 



A second major goal will be the development of a program for a transient 

 wave with linear sweep rate, constant amplitude over the frequency range of in- 

 terest, and smooth starting and ending, so as to minimize initial and terminal 

 transients and the extraneous "noise" at the end of the wave train. 



534 



