This research investigates the effects of mechanical loads on bottom-founded and floating offshore wind turbines (OWTs), specifically comparing different floater configurations (TLP and semi-submersible) with bottom-founded turbines (monopile). The study identifies three critical intersections for a fair comparison: the base of the blades, the main shaft, and the yaw system. These intersections allow for the prediction of stresses on components when specific material properties are known, which is often not the case in many turbines.

The modeling program Orcaflex is used to describe the motions and loading of TLP and semi-submersible floating offshore wind turbines (FOWTs). Bluewater Energy Services is currently designing a TLP platform for a wind turbine, and this design, along with a semi-submersible FOWT model, is compared with an IEA 15 MW bottom-fixed turbine. External loads such as waves and wind, generated from North Sea data, are considered. Additionally, the effects of design parameters like weight, waterline area, center of mass, and wind turbine generator (WTG) control settings are taken into account.

The study reveals that the semi-submersible platform is more susceptible to environmental loads, leading to some significant translational and rotational motions. Its stability relies on a large water surface area and a catenary mooring system, resulting in low system stiffness. In contrast, the bottom-fixed and TLP turbines exhibit lower motion fluctuations due to their higher system stiffness. The TLP experiences higher nacelle accelerations compared to the semi-submersible, except for heave acceleration, due to resonance with wave frequencies. Mechanical loadings are significantly influenced by wind speed and the turbine's controller. Before reaching the rated wind speed, mechanical loads increase with environmental loads, while post-rated wind speed, the loads stabilize or even decrease due to the controller's intervention.

Furthermore, the study identifies the driving factors for the lifetime of pitch, yaw, and main bearings. The pitch bearing's equivalent load is predominantly influenced by wind-induced moments, while the yaw bearing's load is largely governed by axial loads from the RNA's weight. The main upwind bearing's load is primarily affected by radial loads, with axial loads becoming more significant as wind loads increase.

The overall conclusion indicates that while platform motions influence system dynamics, their direct effect on mechanical loads is less significant compared to other factors such as wind loads and controller actions. The pitch controller plays a crucial role in managing mechanical loads, particularly for pitch bearings. Nevertheless, the relatively large mean angle of the semi-submersible platform impacts bearing lifetimes. The system's angle, combined with the weight of components, especially for the yaw bearing, is a critical factor in determining their lifetime. These findings are supported by existing literature, confirming the complex interplay between environmental conditions, system motions, and mechanical loadings in offshore wind turbines.

The increasing focus on sustainable living and the need to reduce dependency on fossil fuels has led to a growing interest in renewable energy sources. Among these, the wind energy sector has not only experienced significant growth in terms of numbers but also in size. Larger turbines lead to more severe leading-edge erosion and further increase operation and maintenance costs. To mitigate this problem, the new advanced leading-edge protection has become vital in the wind energy sector. This thesis focuses on the evaluation of two polymer coating materials (PA and PD) using a Pulsating Jet Erosion Test (PJET) setup.

The first aim of this thesis is to propose a novel analysis method to address the issue of volume interdependence in the PJET. To achieve this, a concept called "equivalent velocity" is introduced. The equivalent velocity represents the velocity at which a spherical droplet should impact a surface to exert the same kinetic energy per impingement as the actual water slug moving at the impact velocity. By utilizing this concept, the velocity-number of impacts plot takes into account the volume interdependence in erosion experiments.

The second aim is to utilize the PJET to analyze the erosion behavior of PA and PD coatings. The investigation focuses on understanding the relationship between impact velocity and the number of impacts until the incubation period and the breakthrough. The incubation period refers to the interval until the damage is visible and the breakthrough is the moment until the filler underneath the coating is exposed. Additionally, the erosion damage progression of the coatings was analyzed, and the lifetime prediction was evaluated using an existing long-term leading-edge rain erosion model.

The experimental results revealed that the ductile material (PD) exhibits a longer resistance to erosion compared to the stiff material (PA), with the mean number of impacts until breakthrough being 2 to 3 times higher for PD. Moreover, the long-term leading-edge rain erosion model highlights the importance of the accurate measurement of material properties, as lifetime prediction is very sensitive to ultimate tensile strength and Poisson’s ratio.

However, it is crucial to validate the equivalent velocity method through experiments and numerical modeling, while also improving the experimental method to allow for continuous observation of the erosion process in a controlled environment with temperature and humidity regulation. Conducting tests in a wider range of velocities is also recommended. Additionally, improvements for the rain erosion model are necessary to accommodate the utilization of the equivalent velocity.