Modelling mechanical behavior of offshore floating solar concepts

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The world is currently in a global energy transition. To reach the global energy goals requires massive deployment of clean and efficient energy technologies. The use of solar photovoltaic (PV) therefore has to be scaled up. Offshore deployment of floating PV would be a suitable solution. There are currently different concepts in development for offshore floating PV. One solution is to design the offshore floating solar structures using interconnected rectangular floaters on which the solar panels are mounted. Multiple design choices have to be considered, such as the size of the structure and the design of the connections between the floaters. The main aspect to consider are the forces that arise in the connections due to the motions and loading of the offshore floating solar structure in the waves.

One of the main challenges is to quantify the effect of the different design choices regarding size and connection compliance on the forces within the connections between the floaters. The aim of this research is to give insight into the interaction between connection forces and different concept choices regarding the size of the floaters and the compliance of the connections between the floaters.

A numerical model of two floaters which are connected with two connections at each end of the structure is developed. The forces and motions of the floating structure are computed using numerical tools in the frequency domain. The hydrodynamic coefficients and wave excitation forces are obtained using the boundary element method software NEMOH. The connections between the floaters are modelled as a set of linear translational and rotational springs in each degree of freedom. The results are validated using earlier studies.

The influence of the design choices is investigated for application at the North sea for different wave directions. First, four different dimensions are varied, the length, the width and the draft of the floaters and the size of the gap between the floaters. The results are then analyzed and compared for each dimension. The comparison of the results shows the influence of each dimension on the force in the connections. Secondly, the connection stiffness is varied in four different directions, the axial, shear, bending and torsional stiffness. The comparison of the results show the interaction between connection stiffness and resulting forces in the connections.

The developed numerical frequency domain model shows the interaction between forces and moments in the connections and different design choices. The results can be used to give an insight into the occurring forces within the connections between two floater for application in the North sea.