Offshore wind stands as a crucial contributor to generating clean, renewable energy, but the limited availability of shallow water locations restrains the potential of bottom-fixed wind. To unlock the vast wind energy potential in deeper waters, a substantial reduction in the Levelized cost of energy (LCOE) of floating wind technology is necessary. Tension leg platform (TLP) floating offshore wind turbines (FOWTs) offer significant cost-saving potential, positioning them as a promising solution. However, achieving cost-effective installation of TLP FOWTs poses significant challenges. In the existing literature, this remains relatively undressed with only two studies focusing on this subject, providing partial solutions

The overachieving goal of the thesis is to address this challenge by conducting an in-depth design space exploration (DSE) of an innovative special-purpose installation vessel along with a robust installation method, offering a cost-effective solution. Floating wind represents a yet-to-be-explored market, presenting design challenges associated with managing uncertainties in operational conditions and TLP designs it intends to commission. The research is conducted within the framework of systems engineering.

During the literature phase, a needs analysis is performed to establish design requirements. The installation vessel must be capable of transporting future fully assembled TLP FOWTs. These include 20 MW wind turbines, three-legged TLPs, and an innovative TLP design with one foldable leg for efficient stacking onboard. The DSE model comprises a two-step design approach and a design evaluation based on scenario modeling. The first design step explores radically different designs using an exploration approach integrated with morphological mapping. A trade-off analysis led to the Windchanger concept featuring an installation deck (ID) integrated with the stern design, employing a winch system for FOWT lowering and recovery. In the second design step, this concept is subjected to further exploration through a parametric model, including generating the hull surface for extensive stability calculations. The key factors for scenario modeling comprise the distance to the port, the operational area, and the TLP design. By evaluating the cost-effectiveness and installation duration in each scenario, the goal is to gain insights into the optimal design ranges. This serves as the basis for establishing a design decision framework to manage the considered uncertainties.

The results of this research offer valuable insights into both the technical feasibility and the cost-effectiveness of the Windchanger concept, facilitating optimal design decisions. The model enables evaluation across diverse scenarios to identify the most suitable design within predefined parameters. This is showcased by assessing performance in two operational areas: the North Sea and the U.S. East Coast. The optimal design ranges derived from these analyses can guide further development of the Windchanger Concept, highlighting that a transport capacity of 2 emerges as the most cost-effective option based on the scenarios evaluated.

Introducing a new installation solution necessitates benchmarking against existing methods to ensure cost-effectiveness and feasibility. The results reveal that TLP foundation costs are approximately 40 percent lower than other floating foundations, confirming the anticipated cost-saving potential. Installation costs represent only a fraction, ranging from 0.5% to 1% of foundation costs, emphasizing the importance of robustness and installation time in cost-effectiveness. The model demonstrates that the Windchanger concept outperforms other TLP installation methods, with lower installation costs per FOWT and a significantly higher number of yearly installations. These findings underscore the Windchanger concept's robustness and cost-effectiveness, potentially leading to a substantial reduction in the LCOE of floating wind.

This research investigated the feasibility of designing an on-board system for the installation of fully assembled Tension Leg Platform Floating Offshore Wind Turbines (TLP FOWTs). The study aimed to identify a potential design that would enhance the overall feasibility of such installations, which required a combination of a literature review, a design methodology, and a concept evaluation.

The main research questions guided the study, focusing on the essential design elements and systems needed for the installation process. Key insights from the literature review helped form a basis for answering the first four sub-questions, while the subsequent sub-questions were addressed through concept development and analysis. The most crucial design decisions revolved around the connection between the installation deck and the ship and the selection of the actuating system.

Multiple concepts were developed, all incorporating a three-beam parallelogram configuration. A load analysis established an installation method and indicated three critical scenarios during the whole procedure. Force analysis, based on the load analysis, revealed two designs as the most feasible. This analysis provided crucial information on the direction and magnitude of forces within the system, guiding further refinement. Further specification of these designs addressed critical parameters, including the dimensions and structure of the beams, the size of the actuating system, and the integration of water ballast.

The study identified two potential solutions. One concept featured an additional framework within the three-beam configuration, optimising force distribution and introducing compressive forces in the actuating system, making a hydraulic cylinder the best choice. The other concept consisted of a simpler three-beam configuration, where the actuating system faced only tensile forces, making a winch system the most suitable solution.

The design methodology structured the development of these concepts, with analyses providing critical insights for further refinement. This iterative process highlighted the advantages and challenges of each concept.

In conclusion, this thesis contributed significantly to the current understanding of TLP FOWT installation by proposing potential solutions for the on-board installation system and identifying future research directions. Through its systematic approach and iterative design process, this research laid the groundwork for further advancements in the installation of TLP FOWTs.

Due to the growing demand for offshore wind energy and the increasing wind turbine sizes, a shortage of capable installation vessels is anticipated by 2024. Consequently, the utilisation of heavy-lift vessels, previously not employed for bottom-founded or floating offshore wind turbine installations, may become imperative to realise the offshore wind project pipeline. Therefore, this study analyses the technical and economic feasibility of installing floating wind turbines with the largest construction vessel in the world named the Pioneering Spirit. For this, the concept development stage of the systems engineering method was applied, consisting of three successive phases. Firstly, in the Needs Analysis phase, valuable insights regarding the operational environment were obtained, resulting in operational requirements for the concept design. Secondly, in the Concept Exploration phase, these requirements were used for generating multiple alternative concept options after which the most promising concepts were selected for further analysis through a trade-off analysis. Lastly, in the Concept Definition phase, the technical feasibility, workability and economic feasibility were evaluated for the selected concepts. The technical feasibility was assessed by creating storyboards for the different installation procedures, determining the stability of the barge named the Iron Lady for different load cases and providing technical descriptions of performed operations and required equipment. Furthermore, the workability was estimated by comparing statistical wave and wind data with the environmental limits for various operations obtained through literature, previous projects and a motion analysis model. Subsequently, with the storyboards and workability results, the economic feasibility was determined with a model that included estimations of the vessel and fuel costs for constructing a reference wind farm located at a variable distance to shore. Ultimately, it was found that Spar- and TLP-type floating wind turbines are of most interest for the concept design and that the Pioneering Spirit is in principle capable of installing the corresponding pre-assembled foundations and wind turbines relating to a capacity of 15 megawatt with a single-lift operation. Furthermore, this research gives valuable insights that extend beyond the initial scope of this paper. Since the performance implications of the selected concepts related to the workability assessment and economic feasibility study can directly be linked to specific design choices and limitations. This, in combination with the exploration of floating wind turbine installation with alternative lifting equipment, can be used to provide recommendations for future designs of purpose-built vessels in this sector. Finally, the methodology used in this study could be applied to evaluate the feasibility of other potential concepts for deployment in this area.