Very flexible floating structures have been proposed for offshore floating photovoltaics installation. Characterized by having structural lengths much longer than wavelengths, small thickness, and low bending stiffness, these structures are prone to large vertical deflections and strong hydroelastic interactions. Experimental information on these structures is scarce. In this study, we employed digital image correlation (DIC) to investigate the hydroelastic interaction of a flexible floating sheet with a length-to-height ratio of 1,000 in regular long-crested head waves. The wavelength was one-tenth and one-fifth of the structure length, with a wave steepness of 0.04. The repeatability of wave conditions and measurement results was demonstrated, and measurement errors were quantified. Surface elevations showed that the sheet followed a local wave elevation in long waves. In shorter waves, strong hydroelastic interactions led to wave lengthening underneath the floating structure and three-dimensional (3D) effects across the structure width. Wave lengthening agreed well with prediction from the hydroelastic dispersion relation. Observed 3D effects necessitate further research into the possible influence of viscoelastic effects. It was shown that the DIC technique is suitable to measure flexible floating structures in waves with low error and good repeatability. Experimental data are publicly available.
Over the past decennia, investigation of the hydroelastic response of floating structures has been mainly motivated by research on sea ice and very large floating structures (VLFSs); see the reviews by Karmakar et al. (2011) as well as Squire (2007, 2011), Chen et al. (2006), and Lamas-Pardo et al. (2015). More recently, hydroelasticity has received renewed attention with the rise of (offshore) floating photovoltaics (FPVs). Large modular floating structures for rigid photovoltaic (PV) panels are envisaged in various projects, as summarized by Trapani and Redón Santafé (2015). Flexible structures for FPVs based on thin-film PV modules have been demonstrated to have technical and economic potential (Trapani et al., 2013; Trapani and Millar, 2014).