30 



Output Locations 



The spacing of the desired output locations must be chosen to determine the 

 placement of the windows. The solution in each window is expected to be most 

 accurate in the center, and thus a separate window is centered at each location where 

 output is desired. As each window is computed independently, there is no restriction 

 on the spacing of the output windows. 



Non-Dimensionalization 



The comparisons of the errors in equations of different dimensional quantities may 

 result in spurious solutions that over emphasize certain equations in the formulation. 

 While the familiar dimensional forms of the equations have been presented here for 

 clarity, all parameters and variables are non-dimensionalized by physically identifiable 

 parameters before computation. The mass density of water (p), acceleration of gravity 

 (g), and the mean zero crossing frequency of the measured record (cj-) are used to 

 define characteristic length, time and mass scales. 



Length scale = g/u;l 

 Time scale = 1/u;, (3.7) 



Mass scale = — — 



z 



3.3.2 Optimization Procedure 



The primary process in the LFI method is a nonlinear optimization of a system 

 typically involving up to 14 algebraic equations in 12 unknown parameters. A system 

 as complex as this may have numerous local minima that result in spurious solutions. 

 The best way to avoid these solutions, and to ensure efficient optimization, is to start 

 with a good estimate for the unknowns in the system, and, in addition, to have a set 

 of criteria for identifying spurious solutions. 



