Offshore wind farms are central to the global energy transition, especially as larger turbines and new substructures enable deployment at greater depths. While cost and energy yield are typically the main drivers of design, integrating environmental impacts into the design process is becoming increasingly important. This thesis develops a framework in which life cycle greenhouse gas (GHG) emissions are quantified and expressed through the global warming potential (GWP) in grams of CO₂-equivalent per kWh, thereby creating a metric that can be directly compared with the levelized cost of energy (LCOE). In doing so, GWP becomes a design-relevant parameter for optimizing offshore wind farms not only for economics, but also for sustainability.
The study investigates wind farms ranging from 400 MW to 1000 MW, with turbine ratings of 5 MW, 10 MW, 15 MW, and 22 MW. Three foundation types are considered: monopile (fixed-bottom), semi-submersible (floating), and spar buoy (floating). A bottom-up life cycle assessment (LCA) was applied, covering material production, manufacturing, transport, installation, operation, and decommissioning. The assessment incorporates a logistics model for marine operations and farm-level scaling to ensure realistic representation of installation demands and component quantities. Results were normalized by the annual energy production (AEP) of each configuration, enabling fair comparison across technologies and site conditions.
Findings show that increasing turbine size consistently reduces GWP, as fewer units are needed to achieve a given farm capacity, lowering both material requirements and installation activities. In a 400 MW farm, semi-submersible turbines achieve GWP reductions of 50.50%, 65.28%, and 73.96% when scaling from 5 MW to 10 MW, 15 MW, and 22 MW, respectively. Spar buoy turbines show similar reductions of 50.91%, 67.29%, and 75.93%. For monopile foundations, also considered at shallower depths, larger turbines likewise reduce environmental impacts per kWh. Expanding farm capacity from 400 MW to 1000 MW further enhances performance, as economies of scale amplify both environmental and economic benefits.
Economic analysis reveals parallel trends. LCOE decreases with turbine scaling for all foundation types, although monopiles remain most competitive in shallow waters, while spar buoys gain advantage in deeper sites. Semi-submersibles bridge the intermediate depths but also benefit significantly from turbine upscaling. The alignment between GWP and LCOE trends indicates that design decisions favoring cost reductions also contribute to environmental sustainability. However, the marginal reduction in GWP diminishes at very high turbine ratings, suggesting that beyond a threshold, other factors such as LCOE, reliability and system integration may dominate design trade-offs.
In conclusion, this thesis demonstrates that by quantifying environmental impacts into a comparable metric, sustainability can be incorporated into wind farm design. Across farm scales, turbine ratings, and foundation types, results consistently show that larger turbines on monopile, semi-submersible, and spar foundations deliver lower GWP and improved LCOE, confirming that technology scaling serves both economic and environmental objectives in offshore wind development.

This research investigates the feasibility of bamboo fibre-reinforced bio-derived polycarbonate composites for secondary aerospace applications. Motivated by the need for sustainable alternatives to synthetic composites, the study focuses on the effects of chemical fibre treatments on mechanical, thermal, and interfacial performance. Bamboo fibres were treated using alkali (2–8% w/v), silane (2-8g/L), and acetylation methods. Acetylated fibres were excluded early due to structural degradation.

Comprehensive fibre characterisation included density, water absorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fibre tensile testing. Notably, 2% NaOH-treated fibres exhibited a tensile strength of 249 MPa, and 5 g/L silane-treated fibres reached 194 MPa, compared to 110 MPa for untreated fibres. TGA showed improved thermal stability with onset degradation temperatures of 277◦C for 5 g/L silane compared to 267◦C for untreated fibres.

Treated fibres were used to fabricate unidirectional laminates via solvent-based prepreg processing with Durabio, followed by compression moulding. Composite testing included tensile, flexural, and microscopic cross-sectional analysis. The highest tensile strength of 162 MPa and flexural strength of 184 MPa were recorded for composites with 2 g/L silane-treated fibres, with 5 and 8 g/L silane laminates being only slightly lower than that. Untreated composites recorded 121 MPa and 154 MPa, respectively. Void content decreased from 21% for untreated to 18% for silane-treated, accompanied by a bonding efficiency of 95% for the 5 g/L silane laminate, indicating significantly improved fibre-matrix bonding efficiency. This was supported by optical microscopy, which showed more cohesive interfaces and reduced delamination in silane-treated laminates. Alkali-treated fibres, however, consistently showed worsening properties and quality on the composite level due to fibre degradation and poor bonding.

The study concludes that silane treatment, particularly at 2 g/L, enhances fibre-matrix compatibility, leading to superior composite performance. Future work is recommended in areas including environmental durability, manufacturing optimisation, and closed-loop recycling, with potential expansion to other bio-based matrices.

Bird strike simulations require accurate information about the nonlinear material properties of the bird and structure, dynamic changes in contact between bird and structure, and large displacements and rotations of the structural elements. The soft-body nature of birds allows it to flow fluidly upon impact, making accurate simulation validation difficult. Setting up a model requires evaluating and considering a large number of parameters. To simplify the process of obtaining validated bird strike models, a set of guidelines for setting up the simulations, covering the major parameters that influence the validation of the models, is established. This was done for an EWVT-SPH (Element Weighted Voronoi Tessellation Smoothed Particle Hydrodynamics) bird model by following the building block approach laid out by the aerospace standards of SAE-G28 for both rigid and complaint target structures.

Emerging in the domain of composite manufacturing, thermoplastic polymers can enable the reduction of process times, costs, and waste. In this study, lifecycle assessment (LCA) is used to evaluate a design for a carbon fibre-reinforced thermoplastic (CFRTP) wing rib, made from carbon fibre and polyetherketoneketone (CF/PEKK). The CF/PEKK rib is compared to several hypothetical alternatives, considering autoclave and resin transfer moulding of CF/epoxy and milled aluminium alloy.

The comparison uses novel and state-of-the-art techniques. Using scenario analysis, several perspectives are considered: recyclability, mass-induced energy demand, and alternative energy carriers. The analysis of energy carriers and end-of-life processes incorporates prospective methods to explore the effects of the energy transition. Across these scenarios, it was found that, when there is a mass difference among alternatives of 2% or more, the lighter alternative will be preferred, regardless of other factors. Through sensitivity analyses, potential was found for this margin to grow to 3% under extreme conditions, and to around 5-10% when shifting the whole lifecycle into the future. When dealing with smaller mass differences, material production and manufacturing waste become distinguishers of environmental performance.

These insights are valuable when exploring novel materials and manufacturing methods for commercial aviation. The approach defined in this thesis can be extended to any other application which has a lightweighting imperative, such as automotive, shipping, rail, or wind turbines. Building on this thesis, guidance can be provided on how and where to apply novel materials across multiple product lifecycles.

Laser-assisted fiber placement (LAFP) is an automated manufacturing technique with promising potential to produce larger aerospace structural components using thermoplastic composites. However, during the rapid heating phase, deconsolidation of composite tapes can occur, resulting in negative effects on bond forming ability. This study aimed to investigate the effect of LAFP process parameters on the rapid laser heating deconsolidation forms of CF/PEEK tape samples by developing an experimental setup. Six different combinations of placement speed and consolidation pressure were tested, and the specimens were characterized for roughness, degree of effective intimate contact (DEIC), void content, and thickness. The results showed that an increase in placement speed and pressure can yield a positive effect on the resolvement of deconsolidation. The nip-point temperature was found to have a significant influence, with expected higher temperatures resulting in better re-compaction of the fiber bed and flow of the matrix material. The developed experimental setup provides a foundation for further investigation into the in-situ consolidation of LAFP for meeting aerospace standards.

Launch vehicle structures are commonly composed of cylindrical and conical shells, which are inherently sensitive to buckling. The axial compression experienced during launch can consequently be a sizing load case, so it is important to understand the axial buckling behavior of these shells. Experimental testing is an essential part of studying this phenomenon because manufacturing imperfections can cause large discrepancies between theory and reality. In addition, conical shells have been researched less frequently than cylindrical shells, such that their behavior is less well understood. Experimental testing of launch vehicle structures is difficult and expensive due to their large size, hence it is preferred to test reduced-scale shells, representative of the full-scale ones. In this thesis, a scaling methodology is developed which allows designing representative reduced-scale conical shells for full-scale composite conical shells buckling in axial compression. The conical shells are assumed to have a symmetric, balanced layup with negligible flexural anisotropy. The scaling methodology is developed using the nondimensional governing equations, obtained through Nemeth's procedure, which allows to directly use the coefficients of the equations as scaling parameters. It also provides a framework to not only compare the buckling load of the shells of different sizes, but also the displacement upon buckling, the deformation shape, and the radial displacement. The methodology is set up such that the reduced-scale design parameters are determined sequentially. The buckling behavior of the two shells is compared using a semi-analytical approach, linear eigenvalue, and implicit dynamic finite element analyses. The eigenmode imperfection sensitivity is also evaluated. The methodology is successfully applied to isotropic, cross-ply, quasi-isotropic, and sandwich conical shells. The prediction accuracy is mainly affected by not being able to simultaneously satisfy all scaling parameters, by non-negligible flexural anisotropy and transverse shear, and by differences in imperfection sensitivity between the full-scale and reduced-scale shells. In any case, accurate results are obtained for the considered shells. The radial displacement is most difficult to predict, which is attributed to the membrane prebuckling assumption and neglecting the presence of imperfections. Finally, it is observed that larger eigenmode imperfections affect the accuracy, but they do not cause the methodology to fail. For future work, it is recommended to validate the methodology through experimental testing.

Wind turbine blades are composed of complex composite material structures that are difficult to recycle at the end of their operational lifetime. As such, they are oftentimes landfilled or incinerated. Following the Circular Economy principles, there are a multitude of strategies that may be applied to these structures; these range from more to less desirable, where landfill and incineration are categorised as least desirable. In the ambition to reduce greenhouse gas emissions and reach agreed upon climate goals, the implementation of wind power plays a central role in the Netherlands, and hence the number of end-of-life wind turbine blades will significantly increase in the coming decades. In an attempt to better manage this issue, the creation of a central circular hub as treatment facility for these end-of-life blades has been suggested. Hence, a framework is developed to compare ports with regard to their suitability for the development of a circular wind hub. The framework is based on six categories: port willingness, available space, existing companies and infrastructure, accessibility, focus on circular strategies, and centrality with respect to return volumes. Subsequently, different ports in the Netherlands are compared for the establishment of a circular wind hub. The Port of Den Helder and Port of Amsterdam come forward as most suitable locations, with a strong willingness and being most centrally located. However, it is also highlighted that the hub need not be limited to one single location - in fact, it could be valuable to collaborate and create synergies across ports. Additionally, interregional collaboration with neighbouring countries of the Netherlands – Germany, Denmark, the United Kingdom, France, and Belgium – will help to improve the economic viability of such a hub. This research therefore performs a geographical explicit quantification of the availability of end-of-life wind turbine blades in this region between 2020-2050, and places the results in the context of three circular strategies based on reusing, repurposing and recycling the blades, respectively. This is done through the use of a dynamic Material Flow Analysis and the use of a Geographic Information System. The results indicate a clear increase in end-of-life wind turbine blades in the defined region until 2050, reaching a cumulative amount of 690 kilotonnes by 2050. Application of the circular strategies strongly influences the amount of material for which it is economically viable to be treated in the hub. In all cases, this is significantly lower than the total amount of material in the region. Among the three strategies, reusing the blades results in the highest amount of material treated, energy saved and economic benefits realised. However, the potential market size seems largest for recycling the blades and smallest for reusing them; hence regulation for this disparity is called for. Furthermore, a push is needed for the viable volumes under application of the circular strategies to better approach the total volume in the region. To accomplish this, it is imperative that the economic value of the secondary material be increased, as well as the documentation of wind turbine blades and transparency in the value chain be improved. All in all, this research expresses the urgency, feasibility and potential value of the development of a circular wind hub for end-of-life wind turbine blades in the Netherlands.

Welding is a joining method for thermoplastic composites (TPCs) that offers multiple advantages over the more traditional methods of mechanical fastening and adhesive bonding. A particularly promising welding technique is ultrasonic welding, which features very short process times as a result of the high heating rates that can be achieved. This spot welding technique is hypothesized to have potential for improved damage tolerance compared to more commonly used continuous welding techniques: in a multi-spot welded joint, evolving damage will need to re-initiate in subsequent spots. The fact that damage initiation will need to occur multiple times might delay overall damage evolution through the joint compared to a continuous welded joint, where damage initiation needs to occur only once. This work is a first exploratory step into the domain of fatigue of multi-spot welded joints in TPCs. Existing research on the fatigue behavior of four-spot welded steel joints in various layouts served as the main reference throughout this research: its methodology was transferred to four-spot welded joints in TPCs. By comparing fatigue behavior across both materials, it was evaluated to what extent existing knowledge and design rules for steel could potentially be transferred to TPCs. Differences were observed in the results obtained for TPC and steel joints. Most notably, in steel joints the dominant failure mode was seen to change from spot fracture to sheet fracture at higher fatigue lives. In TPCs, joints consistently showed spot fracture across all load levels. A different interrelation between layout performances was seen in the steel and thermoplastic composite joints, assumed to be a result of localized material strengthening in the steel joints from interference of adjacent heat-affected zones. These results indicate that existing knowledge on multi-spot welded joints in steel cannot be readily transferred to TPCs, as failure modes and material mechanisms may differ. It was discovered that, when one spot failed prematurely as a result of existing damage in the joint, the remaining layout no longer seemed to have an effect on fatigue life performance. This was attributed to asymmetry in the remaining joint layout, meaning one spot would always become a preferred location for damage initiation and subsequent evolution. Therefore, subsequent damage evolution would only be restricted by a single spot up to the point where the shear strength of the joint was exceeded.

Wind energy is one of the cleanest methods of producing electricity. It plays a major role in the transition towards green energy. It is estimated that the installed capacity of wind energy will cover more than 6 % of total global electricity demand by the end of 2019. As the demand grows the requirement for bigger wind turbine also grows. Each year larger wind turbine blades are being manufactured to satisfy the growing demand, resulting in high manufacturing cost and operation and maintenance cost. The main reasons for wind turbine blade failures are poor design, material failure, power regulator failure, extreme load buckling, lightning strikes, foreign object damage and human errors. The failure rate of the wind turbine blade is around 7 % compared to other components of wind turbine. So, an effective and proactive monitoring system for the wind turbine blades becomes necessary due to the large downtime associated with failure and high replacement cost. The main objective of this thesis is to use smeared crack modelling and integrating it with FEM tools (ANSYS 18.2) to identify the damage in the wind turbine blade. The concept that the modal parameters such as natural frequency, mode shape and damping will be affected when a structure is damaged, is used to identify and localize the damaged elements. First, spar cap - shear web assembly is modelled as simple "I" beam in ANSYS. The dimension of the blade is measured from the "NedWind 40 turbine" provided by LM Wind Power. The structure has been modelled using composite materials. The spar cap fibres are laid at 0 ̊ and the fibres of face sheet are laid at ± 45 ̊. One end of the structure is fixed to simulate the actual working conditions. Similarly, the material property of all parts was chosen to represent the actual wind turbine blade. Second, damage is introduced into the structure in the form of microscopic damping into the material property. To incorporate damping into the structure, the loss factor obtained from experiment is used. The damage modelling is done for different severity at different locations of the modelled structure. Third, the eigen value and eigen vector for different microscopic damping coefficient is extracted. Modal damping of the structure is calculated using the extracted eigen value. And eigen vector is used to calculate the phase angle of each elements. The phase angle of each element is plotted to localize the damaged elements. The results show that this method is suitable for identifying defects near the fixed end and in the midsection of a wind turbine blade. Also,1st flap wise and edge wise bending frequencies are suitable for identifying the defects near the fixed end and 2nd flap wise bending frequency is suitable for identifying the defect near the mid area.

Automated tape or fiber placement (ATP/AFP) with in-situ consolidation has been identified as a promising manufacturing technique for thermoplastic (TP) composites, which are highly in-demand in the aerospace industry for future aircraft structural applications. This manufacturing technique is attractive since it has the potential to eliminate the energy and time consuming autoclave consolidation. However, low quality is one of the biggest challenges in the application of in-situ consolidation. It seems that pressure contribution to the bond quality has received less attention than thermal one. Therefore, this work is initiated to simulate the pressure distribution between the compaction roller and the mandrel.
The objective in this work is to predict the pressure distribution in the contact area between the rubber-covered roller and the mandrel in room temperature by finite element methods (FEM). Rubber material is characterized by mechanical testing and then modeled as hyperelastic material. 3rdd-order Ogden material model is found to well describe the strain- stress behavior of rubber material. The material constants are then implemented in FE models as an input. The pressure distribution is predicted by FE modes and the influence of compaction force, rubber thickness, pre-stretching force on the pressure distribution are discussed, followed by an optimization between compaction force and rubber thickness. Experiments are conducted to validate the FE models regarding the three influencing factors, that are: (a). compaction force, (b). with/without pre-stretching and (c). various rubber thickness. Rubber deformation can be captured by the digital image correlation (DIC) Pressure distribution is obtained from the Prescale pressure measurement film produced by Fujifilm®, which are the films that show different color densities under different pressures. Experimental results of strain and pressure distribution are compared with FEM results, followed by discussions and conclusions.
It can be concluded that pre-stretching force should be used to avoid rubber-roller separation and prevent rubber from moving out to the sides. Both of the compaction force and rubber thickness affects the maximum pressure and contact length linearly. A trade- off between compaction force and rubber thickness can be made based on the force limit of the equipment and pressure requirements.

Future wind turbines require larger rotor blade radius, leading to an increase of rotor swept area. The larger rotor swept area results in more energy production of the wind turbine. Further increase is however limited as a result of the structural weight, which induces a large bending moment and could result in buckling of the rotor blade. An innovative design solution resulting in a lower weight blade design could be acquired by introducing a grid stiffened structure as a substitution of the conventional sandwich structure. Design and analysis showed an increase in specific stiffness of the grid stiffened structure for higher loading conditions. In an attempt to validate the obtained results, one sandwich and one orthogrid panel has been manufactured and tested.

Large turbines are a synonym of more energy harvested from the wind, but also of increment in the costs. This dilemma has led many researchers on the field of wind energy to wonder about the optimum size for wind turbines concerning the lowest cost of energy. This project studies the optimum turbine size for offshore applications through the modeling of the costs of the components that have the largest contribution to the Levelized Production Cost (LPC). Since at different power ratings different power densities are optimal, the turbine size is considered in terms of the rotor diameter and the turbine rated power. Therefore, the cost models developed in this work are a function of these two parameters. To develop the cost models, classical scaling approaches are used along with an offshore wind farm design emulator tool. Regarding that the optimum turbine size is not the same for all situations, two case studies of offshore wind farms are established. These case studies contrast some of the relevant characteristics of an offshore wind farm as the power installed capacity, the distance from shore, the water depth, and the wind and wave environment. The optimal size for large, far offshore wind farms was found to be in the range of 10-13 MW, while it was around 5-7 MW for small near shore farms. The optimum turbine size depends mostly on the reduction in the cost of the O&M and the increment in the costs of the turbines and support structure as the turbine scale employed in the wind farm becomes larger. Finally, the blades cost appears to be a limiting factor for the increment in the rotor diameter for the large turbines scales.

A novel continuum damage mechanics model for 2D woven fabrics has been developed and implemented in a VUMAT subroutine for Abaqus/Explicit. The model takes into account the shear non-linearity, the toughening mechanisms associated to tensile failure, and the influence of shear stresses in the initiation and propagation of tensile damage.

The non-linear shear behavior is reproduced by means of a Ramberg-Osgood equation. Permanent deformation, and the degradation of the secant shear modulus associated to the accumulation of matrix damage have been coupled to the formulation of this unidimensional plasticity law. The physical reference required to define completely the shear constitutive response proposed can be obtained from the experimental tensile test of ±45 off-axis coupons. Failure initiation in tension is identified using Hashin's quadratic failure criterion, which accounts for the interaction of shear stresses in the promotion of tensile failure. A bilinear softening relation was selected to represent the combination of fibre breakage and toughening mechanisms characteristic of the intralaminar tensile fracture of these materials. Effort was placed on the development of a procedure for calibrating the softening relation associated to this failure mode. Specifically, this work addresses the applicability of linking the definition of a bilinear tensile damage law in homogenized continuum damage mechanics models for woven composites to the shape of a crack growth resistance curve measured with compact tension tests.

The constitutive model was validated including it in a set of finite element models of unnotched and open hole coupons with different multistacking sequences, under quasi-static tensile loading conditions, and comparing the results obtained by the simulation of the coupons against an experimental benchmark. A good correlation was achieved between the ultimate strength predicted with finite element analysis and the experimental data.

As the demand on new lightweight materials increases due to economic and environmental reasons, fiber reinforced plastics seem an interesting solution. In order to maximize their potential, ways have to be found to introduce damage tolerant designs. To this end, in the present exercise, the damage caused by cyclic loading is investigated.
Cyclic loading causes loss of stiffness and strength of composite structures. In the present work a progressive damage analysis model has been built. Damage is tracked by a macroscopic failure criterion. Failure occurring at levels below the macroscopic level are captured by a degradation theory which requires S-N curves as input. An attempt is made to use S-N curves derived from static tests only. Stress solutions are obtained using a finite element package. In order to bring the macroscopic damage, degradation and stress solution parts together, a cycle jumping algorithm has been developed which minimizes the amount of FEM stress solutions required and the required amount of function evaluations.
In its current form, the model is able to properly predict the trend of stiffness and strength behavior. Showing that a model like this has potential. For the proper predictions of mag- nitudes, additional failure modes should be modeled and the usage of S-N curves obtained from large specimens for applying on smaller geometries (elements) should be reconsidered.

The trailing edge of wind turbine blades are commonly manufactured as an adhesive joint of the pressure-side and suction-side composite panels of the blade. Under some conditions, a lead-to-trailing (LTT) edgewise bending moment can induce buckling at the trailing edge adhesive joint, which may lead to early failure of the blade due to delamination. As a structural instability, buckling in wind turbines has been the focus of much research especially in full-scale tests and more recently at the sub-component level. These higher-level tests, however, are done on pre-manufactured wind turbine blades and require extensive preparation in order to adapt the testing rig to each blade section, as well as incurring into elevated costs.
An additional test level has been suggested for elements and details of wind turbine blades. It has been suggested that this level can fulfill many purposes: New concepts, modifications, material combinations and orientations can be tested, partial safety factors of larger scale tests can be reduced or even certifying minor details of the blade can be done at the element and detail level. As such, the focus of this project is to develop a testing method for a simplified trailing edge bonded joint with a custom designed hinged clamping system upon which a compressive moment can be imposed to induce buckling.
The design of this test will initially be based on a semi-analytical buckling plate model, where in-plane and out-of-plane displacements are coupled through the Von Karman strain-displacement relations. This semi-analytical tool is employed to quickly estimate the buckling loads for plates of varying dimensions. Strain-free imperfections can be included in the model for twisted/pre-bent plates in order to estimate their effect on reducing the load-bearing capacity of the structure. The semi-analytical tool is complemented with FE models for all the design parameters.
The semi-analytical and numerical results are compared to demonstrate the agreement of both approaches aimed to provide a sturdy base for the research. Next, the experimental buckling loads and force-displacement curves are shown against the predictions from the previous approaches with good agreement. Nevertheless, the observable discrepancies between the experimental and numerical results showed that the desired joint-fixity at the boundaries was not fully realized, therefore leading to a slightly different post-buckling behavior. In the end, suggestions are given to improve on the experimental clamping system in order to improve and expand the scope of this research.