Abstract
In this paper, a new particle image velocimetry (PIV)-based measurement method is proposed to obtain the high-resolution tide-induced Lagrangian residual current field in the laboratory. A long gravity wave was generated to simulate the tide in a narrow tank full of water laden with PIV particles. Consecutive charge-coupled device (CCD) images were recorded with the studied layer illuminated with a laser beam. Two images separated by one tidal period were processed by applying the pattern-matching algorithm to get the horizontal tide-induced Lagrangian residual current field. The results coincide with sporadic results from the traditional surface-float tracing method, but with much higher spatial resolution and accuracy. Furthermore, it is found that the direct acquisition of the Lagrangian residual current may reduce the error at least by one order compared with those acquisition methods that require the detailed information of the tidal cycle.
Highlights
In bays and estuaries, the tide-induced residual current, which is generated by the nonlinearity of the tidal system, is an important component in coastal and estuarine circulations (Nihoul and Ronday 1975; Feng 1990)
If the patternmatching algorithm is applied to each pair of frames separated by one tidal period, the high-resolution Lagrangian residual current fields with different initial phases are obtained
To evaluate the Lagrangian residual current field obtained by the particle image velocimetry (PIV) technique, the traditional surface-float tracing method was used as a reference
Summary
The tide-induced residual current, which is generated by the nonlinearity of the tidal system, is an important component in coastal and estuarine circulations (Nihoul and Ronday 1975; Feng 1990). The discussion of the tide-induced residual current is inevitable when studying the Responsible Editor: Birgit Andrea Klein Another definition of the tidally averaged velocity is the quotient of the net displacement of a water parcel after several periods and the elapsed time, namely, the Lagrangian residual velocity. Yasuda (1984) obtained the surface Eulerian residual velocity and Lagrangian residual current in a bay with a sloping bed In all of these studies, the method used to acquire the tide-induced residual current is the surface-float tracing method, i.e., some floats are spread on the surface of the water and the trajectories of the floats are acquired by taking a series of photos in several tidal periods. In the present study, based on the tide-induced Lagrangian residual current theory, a method that enables the acquisition of the high-resolution Lagrangian residual current field through the PIV technique is proposed.
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