The interaction between propagating waves and flexible floating structures remains poorly understood, particularly in terms of interface boundary layer characteristics, which play a role in influencing wave attenuation and energy dissipation. In this study, phase-locked Particle Image Velocimetry was used to capture velocity fields beneath a continuous, compliant structure subjected to regular waves of varying order and steepness. The results confirm the formation of a distinct wave-induced boundary layer at the fluid-structure interface. For second-order waves with low steepness (H/λ=0.02), an adapted form of Stokes’ second problem predicts the boundary layer thickness, velocity overshoot, and exponential decay with depth reasonably well. However, for steeper second-order or third-order waves (H/λ=0.033–0.064), the experimental data reveal significant deviations from the model - specifically in the boundary layer structure and in the slope of the velocity profile for attenuating waves. These discrepancies suggest that classical linear theory is insufficient in capturing the full complexity of wave-structure interactions as wave steepness increases and nonlinear effects become more pronounced. ... Read more

Increasing utilization of ocean space and a global push for renewable energy solutions has spurred interest in wave behavior around Very Large Floating Structures, like floating photovoltaic (PV) systems. Flexible PV modules may be more suitable for the varying wave conditions found in offshore environments. However, while viscoelastic models are commonly used for wave prediction, they show notable discrepancies with experiments, likely due to untested assumptions of inviscid flow. This experimental study aims to fill that gap by investigating both the wave characteristics and velocity fields underneath flexible and rigid structures using simultaneous Particle Image Velocimetry (PIV) and wave elevation measurements. Wave attenuation is observed for short wavelengths over the flexible structure length. The 2nd order Stokes wave theory provides a good approximation of the wave-induced horizontal velocity profiles under the flexible structure but underestimates the velocities under the rigid one which further lacks the typical exponential decay with water depth. The presence of a wave boundary layer is showcased and compared to an adaptation of the Stokes 2nd problem. ... Read more