An Integrated System Combining Very Large Floating Structure, Oscillating Water Column Device and Floating Photovoltaic Plant

This PhD thesis proposed the integration of a Very Large Floating Structure (VLFS), an Oscillating Water Column device (OWC), and a Floating Photovoltaic (FPV) plant to create an offshore artificial island for the exploitation of marine renewables. Fixed Bottom-detached Breakwaters (BDBs) and tension-leg moored Floating Breakwaters (FBs) were studied. The integrated system was proposed to protect an offshore marine area, thus protecting FPV, which allowed the continuous harvesting of solar energy even under extreme wave conditions. Numerical and experimental modelling have been adopted as experimental methodologies for this study. A 2D numerical wave flume (NWF) was developed in Ansys Fluent software environment to be used as the main tool for conducting parametric studies of the proposed VLFS-OWC system. The numerical results have been validated by means of experimental modelling. Physical models have been designed and tested in the Wave-Current Flume of LABIMA at Florence University, Italy. Based on the literature review, the lack of reliable engineering formulations for the accurate prediction of wave transmission of BDBs with large draft (DFB) emerged. The interaction between waves and BDBs was examined under different wavelengths (Lw) and the dimensions of BDBs. An empirical equation was developed to precisely predict the transmission coefficient (kt) by considering the relative width (WFB/Lw) and relative draft (DFB/Lw) in intermediate and deep-water regions. The integration of OWCs in BDB was proposed to convert the wave energy that impacts onto BDB. The dissipation of wave energy in OWC air chamber was studied by analysing the velocity and vorticity flow fields. The influence of OWC design parameters and wave conditions on kt and the Capture Width Efficiency (CWE) of OWC was investigated. Based on the designed dimensions of BDB, FB case was further studied. FBs with vertical and inclined mooring lines were numerically simulated by using an overlapping meshing scheme and tested in NWF. The User Defined Functions (UDFs) for simulating different mooring lines were programmed and compiled in Fluent. The influence of inclined and vertically tensioned mooring lines, as well as the stiffness of the mooring system, on the motion behaviours of FB, transmitted wave, mooring force, and wave-induced force on FB was studied. Considering the lack of analysis of the power performance of FPV plant under offshore wave conditions, a mathematical model was developed to estimate the power performance of FPV plant. This model considered reflection, cooling, shelter, and pitching effects. The mathematical method for estimating the pitch angle of FPV plant under wave impact was developed. Sensitivity analyses of climate conditions (temperature, solar irradiance, wind speed, and altitude angle) and dimensional parameters (distance angle, tilt angle, and width of FPV plant) were carried out. The optimal distance angle was found to be 55°. Single-year environmental data in 2020 and 28-year average environmental data at the selected Mediterranean Sea site in front of the city of Livorno (Italy) were analysed and adopted to estimate the influence of cooling and shelter effects on the power performance of FPV plant. Using the wave-to-wire model, the influence of the time window of Hi on the energy output of FPV-OWC plant was studied. The contribution of OWC plant to the stability of the energy output of FPV-OWC plant was investigated.