Abstract
This dissertation investigates the emerging field of fluid-structure-surface interactions (FSSI), a novel extension of classical fluid-structure interactions (FSI), by examining how the proximity of streamlined objects, such as a rigid flat plate, to a deformable air-water interface fundamentally transforms the system’s vortex-dominated flow dynamics and flow-induced vibrations. By intentionally breaking system symmetry through near-surface placement of the plate, we introduce asymmetric flow boundary conditions that significantly reshape the underlying physics of the system. Our study comprises three interrelated experimental configurations with increasing structural complexity: (1) a stationary flat plate, (2) a plate free to oscillate in the plunging direction (1DoF), and (3) a plate undergoing pitching (1DoF) and coupled pitching-plunging (2DoF) motions. We hypothesize, and our results confirm, that the presence of the deformable free surface significantly changes both flow dynamics around the plate and its structural response, modifying instability thresholds and oscillations of the system. Through advanced flow diagnostics, including planar particle image velocimetry (PIV), volumetric particle tracking velocimetry (PTV), and hydrogen bubble visualization, we demonstrate that the free surface exerts consistent and measurable effects across all scenarios. For the stationary plate, decreasing submergence depth leads to a clear transition from symmetric to asymmetric vortex shedding in the wake of the plate, driven by free-surface proximity. In dynamic cases, our findings show that near-surface placement triggers and sustains self-excited limit-cycle oscillations. Plunging-dominated responses are significantly amplified when the plate is positioned in the proximity of the free surface due to enhanced coupling between vortex dynamics and surface deformation. In contrast, pitching and coupled modes exhibit reduced amplitudes and delayed onset of instability, indicating surface-induced damping effects. Overall, this work establishes FSSI as a distinct and rich domain within fluid-structure interactions, demonstrating that the presence of a deformable free surface fundamentally transforms system behavior. The findings provide new physical insights relevant to marine, aerospace, and energy systems operating near fluid interfaces, where understanding the interaction between structural motion, unsteady flow, and surface deformation is critical.