Development of a Multi-Objective Techno-environomic Optimisation Framework: Design of Floating Platforms and Mooring Lines

The growing global demand for renewable energy is accelerating the development of offshore wind technology, with floating offshore wind turbines (FOWTs) emerging as a key option to harness wind resources in deeper waters. This technology has great potential but is still at an early stage, where high costs, technical complexity, and design uncertainties remain major barriers to large-scale deployment. To make FOWTs a feasible option, optimization is essential to reduce costs and improve performance, while a multidisciplinary approach is required to properly account for the coupled nature and complexity of the system. Within the INF4INiTY project, this thesis develops a multi-objective optimization methodology for the GICON-SOF Tension-Leg Platform supporting the IEA 15-MW reference wind turbine. The approach explores alternative platform configurations by varying the main external dimensions of the substructure, which directly affect structural mass, hydrostatic stiffness, and hydrodynamic response. In parallel, the optimization also accounts for the sizing of the mooring lines, whose dimensions and loads are strongly coupled with the platform geometry. The optimization is implemented using the NSGA-II genetic algorithm, chosen for its ability to explore large design spaces while converging towards Pareto-optimal solutions. The workflow integrates parametric geometry generation in SALOME, hydrodynamic analysis in NEMOH, and simplified techno-economic and environmental models. The optimization framework addresses three objectives: hydrodynamic response, an economic indicator, and an environmental indicator. The design space is explored under stability and feasibility constraints, imposed respectively on platform motions and mooring system characteristics. Preliminary simulations show that both cost and emissions are dominated by steel mass. Refining the cost and emissions functions to capture additional contributions will help decouple these objectives and offer a more realistic view of design trade-offs. The methodology developed in this thesis provides a baseline tool that integrates technical, economic, and environmental objectives, and is ready to be expanded with additional factors such as anchoring systems, installation processes, and end-of-life operations. As part of the INF4INiTY project, this work represents an initial step towards more comprehensive optimization approaches for floating wind platforms.