Experimental study on the estimation methods of wave orbital velocity

The kinematics of a regular wave field has been investigated in order to determine the best mathematical representation. The paper describes the comparison between many theoretical models reported in literature and the experimental results obtained in a bidimensional channel at the laboratory of the Department of Water Engineering of the Polytechnic of Bari. First of ail the classic wave theories have been discussed in order to evaluate the horizontal and vertical velocities. Then, the theoretical models (linear and non-linear), which link wave elevations and velocity components, have been tested by comparing the numerical results with the laboratory LDA measurements carried out in a channel with a sloped bottom. In the present paper the models proposed by Chakrabarti and by Koyama and Iwata have been applied, giving a relationship between time series of velocity components and wave elevations. Furthermore, a linear transfer function between the elevation amplitude spectra and the orbital velocity component ones has been investigated. The waves generated in the channel are regular (i.e. waves with a permanent form) non-linear waves which can be approximated with 2nd order Stokes in the deeper water sections of the channel, following the classic criteria.