SUMMARY OF INFORMATION GAINED FROM SPECTRAL PROGRAMMING 



The following summarizes the results obtained from this exploratory effort: 



1. MASK can simulate unidirectional Gaussian sea conditions which have a specified 

 relative distribution of wave heights and sufficient wave amplitudes to conduct model tests 

 over a range of sea states. 



2. The hydraulic actuator installation is a flexible, reliable method of producing either 

 regular or irregular waves with carefully tailored characteristics. 



3. An important initial requirement for programming using the analog computer technique 

 is that the white noise source have a flat power density spectrum. 



4. Careful attention should be paid to the reduction of unneeded high-frequency energy 

 in programming as well as to electronic limiting, 



5. Because of some nonlinear characteristics in wave generation, the initial attempt to 

 cancel basin frequency-response characteristics should be smooth and approximate. When 

 the initial program is adjusted to generate waves of the desired intensity, spectral analysis 

 will yield a much better second correction, assuming linearity at least about the operating 

 point, 



6. Analog spectral analysis equipment should be used with great care since program cor- 

 rections will be concerned with the difference between two relatively steep curves; this dif- 

 ference is very sensitive to small errors in frequency determination. 



7. A significant limitation in the precision of simulation available is the spatial varia- 

 tion in wave-height spectra in the basin. For future programming, an average spectrum over 

 the normal running path of the model must be defined by making very slow passes with a 

 moving wave-height probe over this track while the random waves are being measured. 



FUTURE DEVELOPMENT 



With the success of the actuator installation in generating random waves with desirable 

 properties, two research programs are underway to make use of this capability. 



GENERATION OF A FAMILY OF UNIDIRECTIONAL SPECTRA 



The Neumann spectrum for fully developed seas causes every average wave height to 

 be related to some frequency of peak wave height in the power density spectrum such that 

 when the seas become rougher, the distribution shifts lower in frequency. An engineer 

 desiring to simulate certain sea conditions at some scale ratio A will select a basin rms wave 

 height which is equal to the full-scale rms wave height divided by A and a basin peak fre- 

 quency which is equal to the full-scale peak frequency multiplied by \/X" • These relations 

 are summarized in Figure 16, which also shows the rms wave heights achieved to date with 

 programs described in this report. From these wave-height results, it is planned to span 



17 



