139 



in 12 equations in 9 unknowns. 



The LFI method has captured the location of the water surface and the kinematics 

 essentially exactly, at only second order. Higher order may be necessary to define the 

 kinematics of a more irregular record, and can be included with little computational 

 penalty. 



6.4.2 Records of Two Intersecting Waves 



Theoretical pressure records were generated by the same fourth order stokes-type 

 intersecting wave theory used in the previous chapter (Ohyama, Jeng, and Hsu 1995a). 

 This method provides the complete kinematics, is applicable in deep water, and as- 

 sumes a zero Eulerian current (see appendix A). 



Standing Wave Figure 6.4 shows the results of the method for a standing wave. 

 The parameters of the Ohyama solution are: period = 10s, first order amplitudes = 

 3ni (resulting in a total wave height of slightly over 6m), propagation directions = 15 

 and 195 degrees from the x axis, in deep water. The pressure array is located 10m 

 below the mean water level. The LFI method applied to third order (J = 3) finds 

 the the water surface and the kinematics at the elevation of 3m below the surface, 

 just below the trough of the wave. While these results show the complete wave, it is 

 important to keep in mind that as with all the previous results, each of the indicated 

 points is in the center of a separate window, and was computed independently of the 

 other windows. In this case, the standard window width was Is {tq = 0.171), with 

 a third order potential function (J = 3), four water surface nodes (M = 4) and six 

 samples on the pressure records (7 = 6) distributed equally in time in each window, 

 resulting in 26 equations in 24 unknowns. 



Short Crested Wave Figure 6.6 shows the results of the method for the short 

 crested wave shown in Figure 6.5 The parameters of the wave are: period = 10s, 

 first order amplitudes = 3m (resulting in a wave height of just over 6m), propagation 

 directions: 30 and 150 degrees from the x axis, in deep water. The pressure array 



