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An additional complexity is the scaling of the bending flexibility, which does not scale properly if the constructions cross sections are geometrically scaled. MARIN is always committed to dealing with these challenges in order to obtain a reliable assessment of the hydrodynamic performance of these floaters.

Numerical simulations Numerical simulations of floating solar constructions in wind, waves and current are necessary for designers in order to be able to optimise their floating concepts. The traditional approach for the analysis of moored offshore constructions, as applied to FPSOs or semi-submersibles for instance, is based on linearised potential flow diffraction calculations, supplemented with Morrison elements when appropriate. The validity of such an approach for these large, lightweight and flexible floating solar constructions needs careful examination and validation with model test data. That tedious task is currently in progress at MARIN, which is combining model test data and numerical simulations from multiple floating solar projects in order to obtain a better understanding of the underlying physics.

Full-scale measurements Full-scale measurements are currently being performed for the Nationaal Consortium Zon op Water. Within this consortium four different concepts for floating solar energy are being investigated. The four systems

are floating on De Slufter which is a large, 260-acre storage site for contaminated sludge in the southwestern part of Rotterdam.

MARIN is involved in the project to assess the mechanical stability of the systems. To make this assessment a wave buoy was installed on De Slufter, together with an anemometer. The floating solar systems were each equipped with five motion response units that measure the motions in six degrees of freedom. In addition, two global positioning sensors were installed on each system. MARIN developed these sensors, which are based on microprocessor technology, specifically for the project. This development fits well within the ambition of MARIN to perform measurements at different levels of accuracy with their corresponding price tags.

Challenging conditions Although not at sea, conditions measured so far have not particularly been benign, with wave heights of up to 1.2 m and wind speeds of 100km/hour.

Measurements on the systems are still ongoing. But we can already conclude that the high wind loads form a challenge for systems that are either relatively high above the water or light. It has furthermore been found that high and steep waves from a direction oblique to the principle hinge lines can pose a problem for connections between different floaters.

Motion and position sensors developed at MARIN based on microprocessor technology

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