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Chapter 5 



Array of Water Surface Traces 



Water surface measurements are difficult to obtain and not very commonly used 

 for field measurements, but they are routinely used in the laboratory. Surface piercing 

 wave gauges are the most commonly and easily deployed of the methods for measuring 

 waves in the lab. Unfortunately, even large arrays of such wave gauges still only give 

 information about the fluctuations of the water surface. The underlying kinematics 

 must still be predicted with a wave theory. The following is a method for determining 

 the kinematics of waves in the region of an array of water surface measurements. It 

 is an extension of the LFI method presented in the previous chapters, expanded to 

 determine the directional structure of the wave field. The method is fully nonlinear, 

 and results in a complete prediction for the full kinematics in the vicinity of an array 

 of water surface measurements, throughout the depth of the water column. 



5.1 Formulation of Solution 



As described in more detail in Chapter 4, the flow is assumed to be irrotational and 

 incompressible, with a potential function that represents either a single directional 

 wave, or two separate intersecting waves. 



When the measurement is taken in a location that is far from reflecting surfaces, 

 it can be effective and straightforward to assume that the wave field can locally 

 be defined as a segnaent of a single steady wave. This is quite similar to the LFI 



