Coupled PIV and PTV Measurements of Particle Velocities and Trajectories for Surface Waves Following a Steady Current

This paper describes kinetic aspects of surface waves propagating with or without a current in a constant water depth. Physical properties of the velocity and trajectory of a water particle during one wave cycle were investigated experimentally using intrusive and nonintrusive measuring techniques. Two optical devices were used for the nonintrusive measuring technique: particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The techniques provided the velocity fields and distributions at various phases and the trajectory of the water particle over one cycle, respectively. The instantaneous velocity from the PIV measurement was compared with that given by a third-order Stokes wave theory. Suitable agreement between the two velocity profiles proves the ability of the PIV technique to accurately measure both temporal and spatial variations of the velocity. The PIV technique was applied to the prediction of particle trajectories in an Eulerian scheme. The significant novel element of our technique is the use of the velocities at surrounding Eulerian grid points to identify a Lagrangian point.