121 



array as computed by the LFI method. 



This solution was computed to third order, with a window width of 1/10 the mean 

 zero crossing period of the record (approximately 0.2s). Four time samples were taken 

 in each window, providing substantial overspecification of the system, and allowing 

 the shape of the water surface to be well defined in each window. The first trough is 

 fairly flat, and the optimization did not converge to a solution quickly with the small 

 window. After the window was widened, the optimization converged quickly to the 

 given results. 



The LFI method has captured the detail of the kinematics of this irregular wave 

 very well. The comparisons to the measured data are given just below the troughs of 

 the wave. Note that the LFI method accurately captured the secondary hump in the 

 vertical velocity (w) near the 2.5s point. The data used to compute the kinematics 

 were the measured water surface. The computed water surface was found from the 

 predicted kinematics, and it matches the measured water surface almost exactly. The 

 accurate computation of the water surface indicates that the predicted kinematics 

 near the surface may, in fact, be more accurate than the predictions at the elevation 

 where the kinematics were measured. This is to be expected, as the data used to 

 compute the solution was measured at the surface, and thus the results should be 

 most accurate there. Achieving the greatest accuracy near the surface can be useful, 

 as the surface is the location where the water velocities and accelerations are greatest. 



Figures 5.39 and 5.40 show the results of the computation in a window near the 

 crest of the wave given in Fig. 5.38. The errors in the DFSBC are of order 10~^, and 

 substantially smaller in the MKFSBC. The computed and measured velocities do not 

 match exactly, but the magnitude and trend are very close. The results are similar 

 in the other windows. 



5.6 Discussion 



The LFI method is an eff'ective and eflficient way to re-create the kinematics of 

 irregular waves from the measurements of an array of wave rods. It is able to capture 

 the kinematics from primarily uni-directional seas as well as the seas near a reflect- 



