To reach the Paris Agreement goals, switching from fossil fuels to renewable energy is inevitable. Wind power has proved to play a critical role in this transition. To speed up this transition, the wind industry must keep innovating. The major part of Wind Turbine Generators (WTGs) is installed by a jack-up which not only has its limitations from an engineering point of view, such as water depth, soil characteristics and lifting capacity but also from a financial point of view. To overcome these limitations, this research aimed at developing an innovative concept design for the installation of offshore WTGs.
A vessel dynamic analysis showed that the Mighty Servant 1 is the most suitable Boskalis vessel to install WTGs from. The same dynamic analysis also highlighted that a motion compensation system is required to mitigate wave-induced dynamics and enabling WTG installation in floating conditions. After developing multiple concepts of motion compensation systems, a multi-criteria analysis in the form of an analytic hierarchy process is performed. It is found that the most promising concept should rely on hydraulic actuators. To find the optimal values of the design parameters of the chosen concept, a kinematic multi-objective optimization is carried out by means of a genetic algorithm. The optimal set of design parameters is selected by taking advantage of the Pareto front, which is computed by using three chosen performance indexes. A model is developed in MATLAB and Simulink to simulate the dynamics of the motions compensation system. The simulated results showed that a controller which uses velocity feed-forward and position feedback is the preferred way to go. The results also highlighted that the required amount of hydraulic power has a great impact on the economic feasibility of the system. Therefore, to reduce the hydraulic power and guarantee the feasibility, a passive system based on a hydraulic accumulator is added. Based on the results of this research, it can be concluded that the next generation offshore wind turbine generator can be motion-compensated with hydraulic actuators including hydraulic accumulators. Further research could be carried out by assessing more installation phases in combination with a wider range of load cases.

In 2022 the first 12 MW offshore wind turbines are expected to be installed. Due to the continuous upscaling of wind turbine generators new problems are expected to arise during the installation of the turbines. Especially the workability of the installation of larger wind turbine blades, which are already causing problems during the installation of 8.4 MW turbine blades, are questioned by Van Oord. This research focuses on the alignment process of the blade with the hub, which is considered to be the limiting factor in installing wind turbine blades. The ultimate goal is to reduce single blade installation times by facilitating the alignment process To investigate how different environmental conditions influence the dynamic behavior of the blade in the alignment process, a numerical model is developed. The motions of the blade, forces in the taglines and aerodynamic forces on the blade are evaluated for different environmental conditions during 30-minute simulations in the time domain. Wind velocity, turbulence intensity and the angle of the incoming wind relative to the blade are environmental parameters that influence the motion of the blade. Results for a 8.4 MW reference turbine blade are compared to a 12 MW turbine blade and conclusions are made concerning the installation workability for larger turbine blades. Results show that the displacement of the blade root is caused by the rotation of the blade and installation tool around its x- and z-axis. The response spectrum of the blade root motions contains a significant amount of energy at the lower frequency part of the spectrum. In this part the first and second natural frequency of the system occur, which correspond to the rotations that are the main causes of the blade root displacement. The effect of wind speed, turbulence and incoming wind angle on the response of the blade is significant. Furthermore simulations are conducted for different rotation angles of the blade in the blade installation tool, which can result in large reduction, around 50%, of blade root motions. The responses of larger turbine blades (length 107 metre) increase compared to a smaller turbine blade (length 80 metre). Workability is expected to decrease due to the increase in blade root motions. Based on the results of the analysis, several improvements are proposed for decreasing the blade root motions using the existing tagline set up. Using a different angle of the blade in the installation tool and increasing the tagline tension both decrease blade root motions. A solution using an extra tagline is proposed and discussed to show how the current setup could be improved.

One way to implement a wind turbine in the sea is to use lattice structures. Since these structures are placed offshore, they must be able to withstand all kinds of loads. It is essential that the eigenfrequencies of the support structure do not correspond to the passing frequencies of the blades and any other dynamic actions. To avoid this the natural frequencies of the structure should be estimated during the design and the objective of this MSc study is the development of an easy to use finite element model to perform the modal analysis of an offshore wind support structure. It was built based on relevant inputs, defining the possible design of the lattice structure. Based on these parameters, the model can be adjusted and a high number of designs can be tested easily.
The model is built in Matlab and consists of several modules, each one representing a different part of the design. The user has access to a main script to enter all necessary inputs. Then the program starts and a second function takes over. This second function is divided into five parts. The first, the definition of the geometry, creates the nodes and elements composing the structure. The second part concerns the creation of matrices characterizing the model. Each element is associated with two matrices: a local element mass matrix and a local element stiffness matrix. Each is computed in a local frame of reference, then rotated and assembled into two global matrices, representing the complete structure. Then, the equivalent stiffness characterizing the soil-piles interaction is calculated in the third part. Depending on the pile size and the soil properties, the equivalent stiffness is determined. Once the matrices completely describe the model, eigenvalues and mode shapes are calculated in the fourth part. The fifth part of the function is the plotting of the structure.
The functionalities of the Matlab tool have been validated and thoroughly checked. Firstly, by comparing the analytical and numerical results of a simplified structure (a clamped beam), and secondly using a complete structural model by comparing the outputs of the program with the outputs of the professional software “Bladed”. All key results are verified. From these verifications, it can be concluded that the characterizing matrices of the structure are correctly defined and that the model correctly represents the modal behaviour of a lattice structure.
The tool is ready to be used for sensitivity studies to verify which parameters most affect the natural frequencies. The model can also be used as a pre-design tool to quickly obtain and test different scenarios for an offshore wind support structure.
Nevertheless, the tool has some limitations such as the restricted number of possible designs/configurations, the assumption that the transition piece is a rigid body, the use of the p-y curves that can overestimate the stiffness of the soil, the non-linearity of the system that does not take into account the variation in time. Recommended future work may address these issues.

Multi-use of offshore platforms is a long-term research challenge which aims to combine food and energy production at sea. Research in this field is in its infancy, literature is scarce and without much cross-referencing. The aim of this thesis has been to develop a coherent set of recommendations for the further development of multi-use platforms, specifically for offshore floating wind energy and salmon aquaculture. A design-oriented approach has been adopted to generate insights regarding multi-use plat- forms. New multi-use concepts were generated and presented, illustrating what a future multi-use farm could look like. Simultaneously, a rigorous decision-making framework was set-up aimed at identifying superior concepts, while systematically producing insights by making explicit the trade-offs which govern the decision. A most preferred concept has been selected and evaluated in more detail, focussing on the identification of engineering challenges and cost-reduction opportunities through comparison of the multi-use concept with stand-alone references. Except for one item, no major technical barriers for the further development of multi-use platforms were identified, given that the challenges associated to the stand-alone activities can be met. This item is the expectation that mooring loads will largely increase by integrating fixed-netting structures in wind energy platforms. A small set of cost-reduction opportunities was discovered, as well as threats to the economic viability. Evaluation of the cost-reduction potential nuanced the view that large opportunities exist in mooring design and shared O&M vessels and demonstrated that the multi-use concept can also lead to additional costs. Most importantly, further study into the availability of optimal sites for multi-use is recommended, because it can be expected that sites optimal for wind energy may be sub-optimal for the production of Atlantic Salmon.