40 



order wave, and the trough kinematics similar to a lower frequency wave. 



Deep Water Figure 3.6 shows the results of the LFI method for an entire deep 

 water wave. The wave was generated by 10th order Fourier wave theory, with param- 

 eters: 100m water depth, 10m wave height, 10s period, and zero Eulerian current, 

 with the pressure record measured 10m below the mean water level. The parameters 

 of the LFI solution are: Primary window width of Is (tq = O.lT,), with a fourth order 

 potential function (J = 4), five samples on the pressure record, and five water surface 

 nodes (/ = A^ = 5), resulting in 15 equations in 12 unknowns in each window. Once 

 again, the LFI solution matches the actual solution essentially exactly. 



3.4.1 Choosing Pcirameters of Solution 



Unlike steady wave theory where only the order requires prior specification, this 

 LFI application requires prior specification of four parameters: 



• Order of the solution (J) 



• Window width (tq) 



• Number of nodes on the water surface (A'^) 



• Number of nodes on the pressure record (/) 



Experimentation has demonstrated that the resulting solutions are not highly sensi- 

 tive to the values of these parameters; however, a reasonable solution will not result 

 if these parameters are not selected judiciously. The experience acquired while devel- 

 oping the LFI method on analytically generated records has provided some guidelines 

 to help select appropriate values. Despite these guidelines, individual judgment must 

 be used when applying the LFI method to a particular measured record. 



Number of Nodes on the Water Surface and Pressure Record Mathemat- 

 ically, the system of equations is specified if there are at least as many equations as 

 unknown parameters. In this case, / -|- A'' > 4 -|- J. While meeting this criterion is 



