RESULTS OF TESTS IN IKREGUIAR WAVES 



As mentioned previously., tests in irregular waves were conducted for 

 simulated State 4 and 6 seas. The irregular wave data provided a more 

 realistic estimation of the performance of the prototype in waves. These 

 test results represent , In a probabilistic sense, the motion of the platform 

 in the particular sea environfnent simulated during the tests. 



Time histories of wave height, pitch angle, roll angle, and heave, 

 surge, and sway accelerations were recorded and spectrum analyzed. It 

 was physically impossible to locate the heave accelerometer at the center 

 of the roll axis. As a result, the determination of heave acceleration, 

 in the beam sea conditions, is actually a measure of the platform's vertical 

 motion approximately 2 feet from the center of the model roll axis. There- 

 fore, the heave motion in the beam sea conditions do not accurately reflect 

 the vertical motion of the platform' s center of gravity particularly in 

 displacement conditions 1 and 2; where the roll motions are large. The 

 heave accelerometer was located at the pitch axis so there is no similar 

 effect in the head sea cOttdition. 



The random wave results are presented in Figures 5 through 28. From 

 these figures, the relative amounts of energy at different frequencies and 

 the frequency at which maximum energy occurs are apparent by obsejrvation. 

 By integrating the areas under the curves, statistical estimates of the 

 various motions can be computed. For example, the area under the spectrum 

 curve is equal to twice the mean square value of the signal: 



Area = E = id^ 

 or the rms = ft/E/2 = a. 

 The average peak-to-peak values are related to the E value as follows; 

 Average value (pteak-to-peak) 



h = 1.77 J^ 

 Average of 1/3 highest value 



h 1/3 = 2.83 ^E 

 Average of 1/10 highest value 

 h 1/10 = 3.60 yF 



