Viscoelastic materials such as rubbers find ubiquitous use in engineering applications due to their outstanding ability to dampen vibrations and shocks. During a load cycle, the stress-strain curve of a viscoelastic material exhibits energy loss due to hysteresis. The structural response is damped because mechanical energy is dissipated and converted into heat, known as self-heating. The heating of the viscoelastic material results in degraded mechanical properties, and eventually, failure. This study focuses on the application of the viscoelastic material polyurethane in roller coaster wheels. Roller coaster wheels typically consist of a cast aluminium rim with a co-bonded polyurethane rubber bandage. The high forces and high speeds of a roller coaster ride lead to high self-heating in the rubber bandage. The high resulting temperatures in the bandage may cause failure of the bond line and of the rubber bandage itself. Replacement of the rubber bandage (re-treading) is a time-consuming and expensive process and ideally avoided. It is known that the design parameters of the wheel (diameter, width, bandage thickness, rubber hardness, etc.) influence the temperatures in the rubber bandage. At the same time, these design parameters have an influence on the damping capacity of the wheel, which is important for passenger comfort, noise and the longevity of the other mechanical components of the roller coaster vehicle. For example, the wheel with the maximum thermal performance (i.e., minimum temperature) will have minimum damping capacity, and vice-versa. To avoid this complication, this study compares the thermal performance of wheels with similar damping capacities. To evaluate the thermal performance of a wheel, a decoupled thermo-structural finite element analysis methodology is implemented. The method is validated using experimental measurements provided by the polyurethane manufacturer. Subsequently, a novel wheel design is proposed and compared to a regular roller coaster wheel. The 𝛽-ratio was introduced as the ratio of thermal to mechanical power. By comparing the finite element results with the experimental results, it was found that 𝛽 = 0.24 ensures that the numerical temperature matches the experimental temperature 𝑇num = 𝑇exp = 319.4 K. This value for the 𝛽-ratio was subsequently applied to finite element analyses of a regular roller coaster wheel and the novel wheel design. The standard wheel reached a temperature of 351.3 K on the surface and 376.7 K internally. The novel wheel design reached a maximum temperature of only 314.2 K. The maximum temperature of the novel wheel design is much lower than that of the standard wheel, because its structural finite element model is much stiffer, therefore providing less damping. Given the same loading cycle, the maximum temperature of the novel wheel design was found to be significantly lower than that of the standard roller coaster wheel. This indicates that the novel wheel will be more durable and have a longer lifetime. However, the novel wheel was also found to be significantly stiffer than the standard wheel. Toward the end of the report, various design iterations of the novel wheel design are considered which decrease this stiffness and improve damping.

Over the past decade, the offshore industry, particularly the wind energy sector, has exhibited continuous growth, emphasizing the escalating significance of sustainability within this domain. The current work seeks to enhance this aspect by exploring offshore access systems featuring composite gangways.

Composite offshore structures however pose challenges due to the involved complex damage mechanisms and the need for novel maintenance procedures, introducing uncertainties concerning their operation. A Structural Health Monitoring (SHM) system is proposed for increasing confidence in the safe operation of the new composite gangway.

The suggested SHM system relies on inverse Finite Element Methods (iFEM) deflection reconstruction using Fiber Optics (FO) strain data. The gangway design is simplified to a U-shaped beam geometry under bending load, modeled using IQS4 elements. Its performance was assessed using mock strain data generated numerically through FEM software.

Deflection reconstruction using both tri-axial and uni-axial strain measurements was investigated, revealing that uni-axial measurements can be sufficient for the current application. The sensing network was streamlined by focusing on line configurations along the length of the beam, leveraging the capabilities of FO sensors.

The introduction of strainless inverse elements highlighted the limitations of strain pre-extrapolation with Smoothed Element Analysis (SEA) for such a geometry. Modeling guidelines and their effect on improving the robustness of SEA are explored. A strain sensing network using four uni-axial sensing lines is found to offer a sufficiently accurate deflection reconstruction for the application.

Aircraft and helicopter structures commonly incorporate a combination of high-strength, low-density materials, such as carbon fiber-reinforced polymer (CFRP) and aluminum alloys, which are joined mechanically (e.g., fasteners, rivets) or physicochemically (e.g., adhesives, welding). While these structures are mechanically optimized, their durability can be compromised by galvanic corrosion when materials with different open circuit potentials are in electrical contact. A typical example of such a joint is the mechanically fastened CFRP-AA2024 connection. This thesis investigates the less understood process of galvanic corrosion using an in-situ reflected microscopy technique combined with electrochemical potential noise, complemented by post-mortem scanning electron microscopy (SEM) and Raman analysis. Additionally, the study explores the use of environmentally sustainable materials to improve the system's eco-friendliness without sacrificing protective performance.

Recent launches of satellite constellations in the Low Earth Orbit (LEO) region have increased the collision probability of existing debris objects with active satellites. Monitoring the trajectories of these debris objects is crucial for Space Situational Awareness (SSA) to prevent the creation of more debris due to unwanted collisions. Much focus is on the LEO regime, with little awareness of the higher Geostationary orbit (GEO) debris population. To date, the explosion of the Russian Ekran 2 satellite in 1978 as well as the disintegration of the Titan IIIC Trans-stage in 1992, have been recorded. These incidents have increased the number of small-sized debris objects in GEO. More unnoticed fragmentation events have been speculated to have occurred, which pose a significant risk of collisions and damage to all weather and communication satellites in use today. The NASA Debris Office confirms that current ground-based radar or optical sensing methods can only be performed for objects of size 1 m and larger, leaving a gap in the precise orbit determination of sub-meter-sized objects in GEO. Moreover, limited observations and atmospheric losses hinder the quality of orbit determination, thus limiting present ground-based SSA techniques. Attempting to bridge this gap in current space surveillance and tracking methods is the objective of this thesis. It evaluates the feasibility of using space-based sensing methods to enhance SSA in the GEO regime. In this research, a satellite in a sub-GEO orbit is deployed to collect in situ radar measurements, which are processed to determine the orbit of a single object in GEO. Different satellite geometries (altitudes and inclinations) and measurement types such as range, range-rate, and direction (azimuth and elevation angles) and combinations thereof have been analysed. A simple grid search optimisation has been performed to assess the feasibility of such a technique and propose a possible favourable observation configuration, which improves the quality and accuracy of orbit determination. It also analyses the uncertainties in the debris state for future epochs to assess the errors in orbit prediction. The limitations of the geometry and measurement model are identified in this study and provided as recommendations and suggestions for further research. INDIGO is hence a feasibility study or a proof-of-concept of space-based debris state observations in GEO. It can be considered a stepping stone towards inventorying the small-sized GEO debris population catalogue and exploring enhanced SSA techniques in the future.

Leading Edge Erosion is a major concern for the wind energy industry as it affects the aerodynamic efficiency of wind turbine blades and, therefore, the power generated. Hail impact on the leading edge could significantly damage the protective layer and the composite substrate. The focus of this research study is to investigate the effect of kinetic energy on the damage mode in gelcoated glass fibre reinforced composite in terms of the velocity and sizes of the hailstone during hail impact. The gelcoated glass fibre composite samples were tested using a gas cannon using parameters based on conditions experienced in real life but with slight modifications to enable accelerated testing. The gelcoated samples were impacted at various velocities for different hailstone sizes, 15mm hailstone (140 m/s, 150 m/s and 160 m/s), 18mm hailstone (100 m/s, 110 m/s, 120 m/s and 140 m/s) and 20mm hailstone (90 m/s) to determine the Failure Threshold Energy (FTE) for each hailstone size considered. This threshold was determined to be the limit below which no damage would be initiated. The kinetic energy of each hailstone is estimated from the mass of the hailstone, and impact velocity, which is measured using a high-speed camera. Using non-contact profilometry (optical microscopy), cross-sectional damage analysis, and ultrasonic C-scan, the damage on gelcoated fibre-reinforced polymer composite samples were analysed.
The coatings did not exhibit any damage or signs of delamination in the coating-substrate interface. However, the substrate showed signs of impact damage. The damage mode was highly influenced by the kinetic energy imparted by hail impact. The damage mode of matrix cracks in the transverse and longitudinal directions was observed in the substrate for most of the impact parameters. The damage mode remained the same for the different hailstone sizes. The impact tests confirmed that a Failure Threshold Energy existed for each hailstone size. It was observed that FTE was increasing with the hailstone size, and it could be stated that multiple impacts had no effect on damage initiation for a limited number of impacts.

The objective of this master project is to improve the current SHM techniques for global damage identification of beam-like composite structures. The studied damage diagnosis method is based on structural vibrations from which the modal parameters are obtained. The literature study provides an overview of the most common vibration-based damage identification methods. The modal curvature shape- and modal strain energy-based methods are selected due to their higher sensitivity to local damages. These methods are applied on an aero-elastically tailored composite wing. High-spatial-resolution modal shapes are extracted from the structure with a state-of-the-art fibre optic strain sensing technology based on Rayleigh back-scattering. Damages are simulated in the wing employing localized mass attachments. The achievable level of damage identification with this technique is found and characterized. The different vibration-based methods are compared and their potential is discussed. It is concluded that the used sensing technique is an excellent choice for global damage diagnosis in composite structures.

This work is a part of the Automated Rotor Blade Inspection (ARBI) project. ARBI aims to improve the rotorcraft RTB process with novel rotor blade measurement equipment. The objective of this research is to investigate how the variation in structural properties of the rotor blades composite structure affects the dynamical response during the RTB process. It is hypothesized that the variation in stiffness and shift in the center of gravity of the structure is caused by in-service defects and repairs.
The results of the NDI inspections give a detailed overview of what type of non-uniformities are found in CH-47 rotor blades. A 2D analytical model is developed to quantify structural blade properties of blades that contain non-uniformities. This model provides the ability to determine the impact of these non-uniformities on the structural parameters based on NDI results and helps to improve the FEM model that is used for RTB simulation.

Impact on composite structures shows a different damage behaviour compared to metal structures. Due to the current short operational life time of composite aircraft the risks of impact damages on composite structures are unknown. This paper proposes a new method for quantitative risk analysis of low velocity impact damages on composite aircraft structures by combining a conventional risk analysis with the probability of detection of the damages. Real damage data of metal structures is used to estimate impactors and to predict damages on composite structures by means of an aircraft impact damage model. To create a large set of impact events and to conduct a more accurate analysis impactor data estimated from the real metal damage data is augmented. Three fuselage sections with a significant difference in amount of damages have been selected to compare the different risk results. The outcome of a conventional risk analysis and the outcome of the probability of detection of damages show that the section with the highest amount of damages results into the highest risk. However, the proposed method by combining the probability of detection of the damages with a conventional risk analysis shows different and more revealing results. The fuselage section with nearly 50% less damages compared to the section with the highest damages appears to be the highest risk section but the difference with the other fuselage sections is small. The proposed risk analysis method intends to be a useful tool for aircraft maintenance organisations for a different approach of assessing the risks of impact damages on composite structures.

Due to the limited availability of sites on both land and sea, there is a need to maximize the power density of wind farms whilst limiting the adverse wake effect between the wind turbines that cause power losses and/or increased load cases. The study focuses on analyzing the potential of combining yaw-based wake-steering and constant blade pitch control down-regulation to mitigate the detrimental wind turbine wake interactions. Data-driven surrogate models based upon polynomial chaos theory have been used to model the statistical distributions of the wind farm power production and short-term Damage Equivalent Loads (DEL) in function of the control inputs. The model calibration data has been generated for a range of control settings for two V27 wind turbines aligned with the wind direction through large eddy simulations using the flowsolver EllipSys3D and the aeroelastic code Flex5. A power-based optimization with DEL constraints has been performed and median power gains ranging from +1% to +3% have been observed at close spacings depending on the severity of the imposed constraints. It was identified that larger power gains corresponded to an increase in DEL. At larger spacings, the wind farm control strategies shows limited performance increases and revert to baseline operations.