Measuring Hydroelastic Deformation of Very Flexible Floating Structures

Sebastian Schreier & Gunnar Jacobi

For Offshore Floating Photovoltaics (OFPV) applications, thin-film PV panels on lightweight floating support structures gain increasing scientific and commercial interest. Over the past years, several different concepts of thin-film OFPV have been proposed, with the common denominator of floating mattress or blanket-like support structures with very little draft in the order of centimeters compared to their width and length in the order of several tens to hundreds of meters. Mostly made from polymer foam materials, these floating support structures are more flexible than the conventional Very Large Floating Structures (VLFS) investigated in 1990s. The flexibility of a floating structure is expressed by the characteristic length derived from the ratio of the structural bending stiffness and the hydrostatic stiffness of the support. For conventional VLFS, this characteristic length is usually longer than the dominant wavelength of the ocean waves, resulting in only moderate structural deflections of the order of 1/10 of the wave height and the total thickness of the structure. The newly proposed structures have characteristic lengths of less than the wavelength of ocean waves. This allows the structures to move with the waves and follow the wave elevation like a floating blanket. Therefore, these structures are classified as Very Flexible Floating Structures (VFFS).

Despite the growing interest in VFFS, little is still known about their hydroelastic deformation and their influence on the surrounding wave field. To start the experimental VFFS research at Delft University of Technology, Digital Image Correlation (DIC) measurements were carried out in this study to investigate the vertical deflection of a VFFS at model scale in a small towing. The model’s characteristic length was 1/3 of the shortest wavelength and it was tested in long-crested regular longitudinal waves. The wavelength varied between 1/10 and 1/5 of the structure lengths. The measurements showed that the structure indeed mostly followed the wave elevation and revealed 3D effects across the structure, which require deeper investigation into wave scattering of VFFS.

Keywords: Offshore Floating PV, Digital Image Correlation (DIC), Hydroelasticity, Wave scattering, Very Flexible Floating Structures (VFFS).

Sebastian graduated from University of Rostock, Germany with a diploma in Mechanical Engineering and specialization in Naval Architecture and Ocean Engineering in 2005. He then started his research on liquid sloshing at University of Rostock and obtained his doctoral degree in Engineering in 2009. From 2009 to 2010, Sebastian spent a year as Post-doctoral Fellow in the Global Center of Excellence program on Aquaculture of Bluefin Tuna and other Cultured Fish at Kinki University, Nara, Japan, where he investigated the flow around net-cages. Thereafter, he returned to University of Rostock as Senior Research Assistant and continued his experimental research of liquid sloshing as well as taught bachelor and master courses in Ocean Engineering. In October 2016, Sebastian joined TU Delft as Assistant Professor in Ship Hydromechanics. Here he focusses his research on experimental hydrodynamics of flexible floating structures with applications in floating offshore solar farms, floating infrastructure, and floating cities.

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