This thesis presents a comprehensive study of Lagrangian and Eulerian mass transport in a wave flume experiment, aiming to improve understanding of mass transport mechanisms and their role in wave-current interactions. This has important implications for nearshore particle transport and pollutant dispersion. The research utilizes state-of-the-art Particle Tracking Velocimetry (PTV) to directly measure the Lagrangian velocity of individual particles, providing higher temporal resolution and precision in capturing unsteady flow phenomena compared to traditional methods. The study compares experimental mass transport data with existing mathematical models, including the irrotational and conduction solutions, and qualitatively discusses the potential importance of the convection model.
The focus of the study is on the temporal evolution of vertical velocity profiles influenced by waves and wave-induced currents, exploring how these profiles change under varying relative water depths (kh)
and wave steepness (ka). Additionally, the temporal evolution of vorticity profiles is examined to identify the underlying mechanisms driving these changes.
To extract the net Lagrangian drift from particle tracking data, three averaging methods—time-averaging, wave-by-wave, and low-pass filtering—are compared. The wave-by-wave method is found to be the most suitable for this study.
The velocity profile transitions from an initially irrotational state, characterized by uniform motion near the surface, to a more complex structure resembling the conduction solution as vorticity diffuses. However, the observed profiles do not quantitatively align with the conduction solution. After approximately 60 minutes, the profile stabilizes but continues to exhibit discrepancies from both the irrotational and conduction models. At equilibrium, while the velocity profiles qualitatively align with the theoretical predictions of the conduction solution, significant quantitative differences remain, particularly in surface drift velocities an the negative peak velocity in the middle of the water column.
The study also shows that as wave steepness increases, deviations from theoretical predictions grow, indicating that higher steepness disrupts the assumptions underlying the conduction solution, leading to greater discrepancies between observed and predicted velocities. The evolution of the velocity profile is further explained through vorticity transport, where a more uniform vorticity distribution is observed compared to predictions from the conduction solution. This complex behavior is influenced by factors such as sidewall interactions and vorticity convection along the direction of wave propagation.