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Chapter 4 



Three Dimensional LFI Theory 



The previous chapters were concerned with the determination of wave kinematics 

 from the analysis of a time series of a single physical quantity at a single location. By 

 assuming that the flow is two dimensional, a reasonable approximation of the wave 

 kinematics can be found. Unfortunately, this analysis does not give any information 

 about the directionality of the sea state. There are some processes in which the wave 

 directions are directly important, such as. sediment transport. Even in situations 

 where the wave directions are not directly important, it has been shown that omitting 

 the directional nature of the sea results in substantial errors in the prediction of scalar 

 quantities, such as the maximum velocities and accelerations in a measured wave crest, 

 or the resultant forcing on structures (Dean 1977; Forristall et al. 1978). 



In order to capture the directional nature of the sea, an array of instruments must 

 be used. The result is a set of time series of a single physical quantity at a number 

 of different locations, or a set of different physical quantities at the same or diiferent 

 locations. This chapter outlines a method for determining the directional kinematics 

 of irregular seas that can be adapted to accommodate virtually any combination of 

 such time series. 



