Hydroelastic response of Very Flexible free Floating Structures in Faraday waves
B. Christiaens (TU Delft - Mechanical Engineering)
S. Schreier – Mentor (TU Delft - Ship Hydromechanics and Structures)
H.M. Pot – Mentor (TU Delft - Ship Hydromechanics)
Willem van De van de Water – Mentor (TU Delft - Fluid Mechanics)
J. Westerweel – Graduation committee member (TU Delft - Fluid Mechanics)
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Abstract
This study investigates the hydroelastic response of very flexible, free-floating membranes in Faraday waves, with a focus on the influence of sheet thickness. The motivation for this work arises from the need to understand wave-structure interactions involving very flexible floating structures (VFFS), which are relevant for applications such as (offshore) floating photovoltaic panels ((O)FPV).
Laboratory-scale experiments were conducted using vertically oscillated membranes of varying thicknesses (20–200 micrometers) floating on a water surface. To ensure a reliable comparison and establish baseline measurements, free-surface reference experiments were first performed using silicone oil, which provided controlled conditions with minimal contamination effects. Additional experiments on deionized water allowed for direct comparison between hydroelastic and purely fluid cases. The experimental setup combined imaging, digital image correlation (DIC), and synthetic Schlieren methods to capture the coupled wave–membrane dynamics. These techniques provided quantitative measurements of both membrane deformation and underlying wave fields, including amplitudes and wavelengths, across a range of excitation frequencies and acceleration amplitudes. This enabled precise determination of the onset of Faraday-wave instabilities and a detailed characterization of the spatial deformation patterns of the floating membranes.
The results demonstrate a strong dependence of hydroelastic behavior on sheet thickness. Increasing thickness enhances the bending stiffness and inertia of the membrane, resulting in longer dominant wavelengths, higher critical accelerations, and modified wave amplitudes compared to very thin membranes. For the thinnest membranes, classified as VFFS, localized wrinkles were observed at low excitation frequencies. Their presence indicates dynamic stress variations and local in-plane tensions induced by wave–membrane interactions, phenomena not captured by standard continuum models. Furthermore, the onset of instabilities and wave amplitude behavior for thicker membranes revealed the combined effects of increased mass and bending stiffness, highlighting the transition from highly compliant to more rigid floating regimes.
Taken together, these findings provide experimental evidence for the critical role of sheet thickness in governing hydroelastic response. The results clarify how very flexible floating structures interact with surface waves and how this interaction evolves as thickness increases. Beyond fundamental fluid–structure physics, this work offers practical insights for the design and modeling of VFFS in engineering applications, such as optimizing the stability of floating photovoltaic modules and controlling wave-induced motion of thin maritime membranes.