Maritime vessel slamming into aerated water is a significant area of study for high-speed and lightweight craft. Upon impact with water, safety risks can lead to structural failures, endangering human life and resulting in economic losses. The design must be optimised for material usage with appropriate safety factors based on accurate knowledge of the loading and response under several impact conditions. Structural flexibility makes hydroelastic effects unavoidable, with the magnitude governed by impact type, velocity, and structure geometry. Entrained air from free-surface breaking renders the water weakly compressible, further altering the slamming dynamics. This work presents a physical foundation and experimental dataset for validating numerical models of more realistic impact conditions.

In this work, a novel experiment was set up for a combined evaluation of hydroelastic slamming in aerated water. A wedge with a 15 degree deadrise angle was designed and constructed to represent ship bow slamming. The wedge bottom consisted of interchangeable steel plates of varying stiffness. Contact and optical measurement techniques were used to capture and visualise the loading and response over the plate width. Experimental test conditions include plate thicknesses between 1 and 3 mm, impact velocities between 2 and 5 m/s and an air fraction in water between 0 and 2 %.

The results show that structural stiffness and impact velocity, captured by the hydroelasticity factor RF jointly govern the slamming response. The air fraction in water redistributes impulsive loads over time and modifies the wetted natural frequency through the influence of water density. For high-velocity impacts with significant plate deformation, as well as for impacts approaching the quasi-static regime, a lower peak strain was found for impacts in aerated water. Furthermore, for the condition where the wetting time approaches the first wetted natural period of the structure, response amplification due to hydroelastic effects was observed, with a further increase in load for the aerated water condition. This study demonstrates that aeration can amplify structural response, making it essential to take into account the physical aeration effects in the design of ship plating for slamming conditions. The structural response was found to capture the underlying physical behaviour more reliably than the pressure measurements alone. The effects of the small-scale experimental setup on the results were also identified and documented in detail.

Lattice materials have been studied extensively for their advantageous mechanical properties like high stiffness-to-weight and strength-to-weight ratios. These properties make them suitable for a multitude of applications like load-bearing structures, energy absorption and impact attenuation. Amongst several planar microarchitectures, the Kagome topology is found to be optimal for effective mechanical properties like macroscopic elastic modulus. However, it has been shown that lattice defects such as nodal misalignments are detrimental to the macroscopic stiffness of the Kagome lattice. From a realistic standpoint, any manufactured lattice is expected to inevitably have these defects, which naturally makes the favorable stiffness properties of the Kagome inaccessible.

This work takes a step towards designing planar lattices with defect insensitive macroscopic stiffness. A novel design strategy is proposed for generating stiff, lightweight and robust lattice materials. The Kagome lattice is chosen as base architecture for the developed designs due to its excellent stiffness-to-weight property and extreme sensitivity towards defects. The generated designs involve appending the Kagome bulk with two unique and carefully designed microarchitectures. The first is a lattice developed using combinatorial design strategies, which demonstrates properties like perturbation-dependent switching between mechanism-states and load-bearing states. The second is a polarised lattice that enables localisation of mechanisms at specific sites of the lattice. This arrangement forms a "composite" lattice which when appropriately designed demonstrates robustness against manufacturing defects.

Development of such an architecture is carried out through an iterative design and analysis process which is based on reformulated matrix methods. A mass-spring model is used in contrast to regular pin-jointed models and a dynamical matrix method is developed as an alternative to traditional matrix analysis. Suitable designs formed out of this iterative process are verified for their stiffness properties using Finite Element models. Robustness against nodal defects is observed in well-designed lattice models. Satisfactory performance of such designs indicates the efficacy of the adopted design strategy which could potentially be applied to any lattice microarchitecture other than Kagome for robustness.

The current frontier of human exploration is space. We have achieved sending rovers to planets and probes throughout the Solar System and beyond into interstellar space, yet the stars seemed to be out of reach. The current fastest man-made object would take thousands of years to travel to the nearest star, Proxima Centauri. However, Breakthrough Starshot presents an engineering challenge to reach it in a generation's time. Recent technological advancements make this possible through ultralight spacecraft equipped with mirror-like sails, known as Lightsails. Due to their structure, these sails could be propelled by lasers up to 20% light speed, or over 200 million km/h.
To achieve the required efficiency, the sails need to exhibit high reflectivity and low mass on the scale of 1g, while covering a surface area of ∼10m2. Some materials and membranes explored in literature have exhibited high reflectivity, but their mass did not comply with the necessary requirements. The most promising current design is a photonic crystal, which interacts with light in a way that maximizes reflectivity and removes material by incorporating cavities into the surface, effectively reducing overall mass.
Current research into photonic crystal Lightsails primarily focuses on the reflectivity of a small segment of a flat lattice. While this is essential, the literature suggests that the full-scale structures will probably behave like traditional sails on sailboats, tending to billow. This prompts us to consider not only the problem of reflectivity on curved surfaces but also mechanical deformations and stresses within a membrane that's 1000 times thinner than a human hair.
This thesis investigates the full-scale design of the Lightsail from both the structural and electromagnetic sides. Firstly, the material, microstructure, and macrostructure of the Lightsail are analyzed to determine stresses and deformations, as well as the optimal shape for stress distribution and efficiency. Then, through topology optimization of shell elements, the main load-carrying "backbone" of the sail is identified. Secondly, optimization of unit cell photonic crystal cavities is performed across the curvature of the sail derived from the previously obtained shape, maximizing the reflectivity. Finally, the thesis proposes a design of the Lightsail that integrates all findings, which is then used to obtain a Figure of Merit value for comparison with designs in existing literature.

This thesis introduces the Discontinuity-Enriched Finite Element Method (DE-FEM) for the modeling of dynamic multiple crack growth problems including branching and merging, as an alternative to eXtended/Generalized Finite Element Method (X/GFEM). DE-FEM differs from X/GFEM by placing the enriched degrees of freedom (DOFs) directly along the discontinuities, and the enrichment functions vanish at standard mesh nodes. This approach allows DE-FEM to preserve the physical meaning of standard mesh nodes and avoid the issues associated with blending elements. Moreover, by adding enrichment directly along the discontinuities, DE-FEM is more straightforward in computer implementation. These properties of DE-FEM facilitate its modeling of complex crack configurations such as the dynamic crack propagation problems with multiple cracks. Here we propose a scheme for dynamic multiple crack propagation using DE-FEM, which covers crack initiation, propagation, and interaction. Numerical examples are provided to validate the effectiveness of DE-FEM in capturing crack patterns that are similar to those observed in other studies. Meanwhile, the reasons for the numerical instabilities observed during crack propagation and methods to mitigate them are also discussed.

inPhocal, a startup company specialized in laser marking, developed a novel optical module to make the depth of focus more than 50mm, and wants to replace ink marking by this laser marking system in the production line when marking information on products. Distortion will always happen when marking 2D patterns onto 3D objects with laser, so deforming the 2D patterns beforehand to make marked pattern keep its shape is necessary. This process is called shape correction. Nowadays, the way to do this shape correction is very complicated and time- consuming. This thesis is focused on providing a new method that can do shape correction easily and fast. In this research, Non-Uniform Rational B-Spline (NURBS) is used in reconstructing the 3D surfaces and the shape correction will be based on these NURBS surfaces. With this NURBS-based shape correction, the pattern can be mapped on to 3D object fast without distortion.

Nanophotonics is the study of structures’ interaction with light with features at or below the nanometer scale. It has gained the interest of many researchers, as it can be used to control the flow of light very effectively in the design of, e.g., solar cells, highly efficient biosensors or lasers. The design of such devices can be non-intuitive and complex and therefore computational tools like topology optimization techniques have been used to improve their designs. However, the topology optimization methods used in the literature often use a density-based representation of the geometry, which often leads to jagged edges. It has been shown in the literature that jagged edges can deteriorate the accuracy of simulation results. Using a level-set method in combination with an enriched finite element method offers a smoother boundary representation than the often used density-based methods. This work aims to develop an analysis and level set optimization for 2D electromagnetic scattering and eigenvalue problems using an enriched finite element method. Furthermore, we showcase that even for a non-conforming discretization, the enriched finite element method achieves the same convergence properties as the standard finite element method with fitted meshes. Finally, we perform topology optimization on the design of both a 2D meta lens and 2D reflector, maximizing their ability to focus light onto a point, using a level set method to define the geometry in combination with the enriched method used in the analysis.

In recent years, the increased need for renewable energy has put more interest in wind energy and therefore in making wind turbines more efficient and building them as efficiently and cheap as possible. Delft Offshore Turbines (DOT) is developing a drivetrain that replaces the heavy and expensive parts in the nacelle of a wind turbine and makes these parts more accessible and aims to improve the reliability of the wind turbines by replacing the parts that are most prone to failure.  Due to the innovative design of their drivetrain, several unknowns still have to be answered since this has never been tried before. One of the most important parts of this drivetrain requires rolling contacts that endure high contact stresses and have to operate for a long time in harsh conditions. These rolling contacts have to be tested and for this, DOT created the Roller Test Bench (RTB) to test different materials and material combinations until failure and to see what type of failure is occurring and what the lifetime of these rollers is. The rollers are a lot smaller compared to the rollers found in the drivetrain to reduce cost and testing time. The scaling of the dimensions has been done several times in different fields of research but it is unclear how this affects the results and how the results translate to the original rollers. In literature some papers have stated that the results scale in a certain way but this has not been proven or the statements have not been argumented in a clear way such that these statements hold no ground.  A rolling contact has several ways that it can fail; wear, deformation, corrosion or fatigue are most commonly found. From the literature study performed in this thesis it has been noted that the main mode of failure in the RTB is rolling contact fatigue since the rollers are smooth, have no lubrication applied, are free of external contaminants and have no significant amount of friction on the surface. With the stress applied and the material used it is also noted that the fatigue will occur after a high amount of cycles and in literature this is also called high-cycle rolling contact fatigue. Experimental testing of such problems takes a very long time, even if the rollers are smaller and are run faster through the load cycles.  With both problems stated, the lack of information on the influence of scaling on fatigue life and the testing of high cycle fatigue, the goal of this thesis was found and it was to find a method to predict the lifetime and wear mechanisms of rolling contacts in the DOT Direct Drive Pump. This method could then be used to figure out how the scaling affects the fatigue life for rolling contacts and make a possible statement of its influence.  From the literature study a numerical modelling method was found that incorporated the microstructure and included both crack initiation and propagation and was able to model high cycle fatigue. This model suited the problem the best and was proven to provide results that agree well with previously performed experiments and their experimental results. This method implemented a Voronoi tessellation to reproduce the microstructure and applied continuum damage mechanics to calculate the damage evolution and apply the damage to the microstructure. A jump-in-cycle method was applied to improve the efficiency of the model and greatly reduce the time to model until failure. The created model is able to reproduce subsurface initiated fatigue and with that produce a scatter and L10 life comparable with previous models and experimental results. The model was validated by comparing the stress distribution, crack formation and the initiation and total lives with other models and data. The model was off the required range since the models uses an homogeneous isotropic material which causes the scatter to be lower.  With the model created and validated, it was applied to several different half-widths to test how the scaling affects the fatigue life. From the results it was noted that for a larger roller size the fatigue life decreases but it has to be noted that further tests, experimental and numerical, have to be done and improvements to the model have to be made such that at some point a correlation can be made between the scaling and the fatigue life. Further recommendations were provided on improving the model and with that creating more reliable results such that a better prediction can be made on how the fatigue life is affected but also to predict the life of a rolling contact.

The demand for faster production times and higher precisions in the industrial automation is ever-increasing. Resonance modes caused by flexural elements in these machines are limiting the maximum bandwidth. Because of this, high-precision motion systems in industrial machines are limited in the maximum operating speed and precision. To improve the performance of these machines, an active vibration control (AVC) system is needed. In present scientific literature, all AVC systems consist of an under-actuated or perfect-actuated setup. However, the damping performance of these systems could be increased by implementing an over-actuated setup. In an over-actuated setup, multiple actuators are used to control one resonance mode. In this way, control inputs for suppressing modes are provided at more efficient locations, which increases the amount of damping. In this thesis, an over-actuation and over-sensing strategy for active damping is proposed. In this new method, a large number of piezoelectric sensors and actuators are used to control the first four vibration modes of a cantilever beam. The damping performance is evaluated in an experimental setup. Finally, the performance of the new topology of sensors and actuators is compared to the state-of-the-art active damping method that uses a perfect-actuation strategy. The improvement of the new method compared to the state-of-the-art method is shown both in time and frequency domain.

Extensive computational resources are required to solve large-scale nonlinear problems having a finite element mesh with a large number of degrees of freedom (DOFs). Model order reduction (MOR) is a technique used to reduce these DOFs, facilitating a faster solution with reasonable accuracy. This work proposes a method for constructing a finite element-based Reduced order model (ROM) by extending the method of modal derivatives (MDs) to analyse nonlinear vibrations of geometrically complex thin-walled structures. We show that the use of MDs is an effective method to capture the geometric nonlinearities that are present in the system. After validating results with the literature, the proposed ROM is applied to the analysis of a Miura-Ori patterned origami structure and the results of the numerical simulation are compared to that of experiments.

The application of Modal Derivatives (MDs) in conventional reduction methods is an effective method to capture geometric nonlinearities in Finite Element Models (FEMs). Reduction methods, in general, are used to effectively reduce the number of unknowns in FEMs for the sake of computational efficiency. We investigated the applicability of three MDs-based reduction methods in parametrically excited and parametric resonating structures, the focus lays on the steady-state responses. Benchmark in this project is a mechanical Frequency Divider (FD) that consists of cascading mechanical components, each of which is excited by the preceding one by means of parametric resonance. After full activation of the FD, a frequency division along the array of resonators is achieved with a factor 2^i at resonator i. The modularity of the FD makes it an excellent candidate for testing the application of component mode synthesis, where each substructure of the cascade is independently reduced and connected to other members via common interface.

Glaucoma is the leading cause of irreversible blindness and in 2040, more than 111 million people are expected to have the disease. Vision loss in glaucoma is caused by the death of retinal ganglion cells (RGCs) primarily in the optic nerve head (ONH). Elevated intraocular pressure (IOP) is a well-known causative risk factor for glaucoma, highlighting the importance of biomechanics in the disease. All current therapies are focused on lowering IOP levels. However, these therapies are not effective for all patients. One limiting factor in the search for new therapies is the lack of knowledge about the cell processes that lead from biomechanical insult to RGC apoptosis. To better understand this relationship, animal models are used and amongst these models, rats are widely-used due to their pathophysiological similarities to human glaucoma. However, there are anatomical differences between the rat and human ONH, and these differences are likely to affect rat ONH biomechanics. Moreover, there are some anatomical alterations occur in the rat ONH due to remodeling and damage in the early stages of the disease. Computational modeling is a suitable approach for characterizing ONH biomechanics due to the complex anatomy of the posterior rat eye and there has been no previous attempt to characterize the glaucomatous rat eye ONH biomechanics. The aim of this thesis is to characterize glaucomatous rat ONH biomechanics by building two individual-specific glaucomatous rat ONH finite element models (FEMs). By comparing the 1st (mean and the 95th percentile) and 3rd (mean and the 5th percentile) principal strains on the anterior ON with previously built healthy rat eye individual-specific FEMs, the effect of geometrical differences occurred due to remodeling and damage in the early stages of the glaucoma were aimed to be better understood. The 1st principal strain (mean and 95th percentile) relative percentage differences between the glaucomatous and healthy rat eyes under the IOP of 30mmHg were found to be 37.74% and 69.66% for the MR04, and 35.66% and 66.02% for the MR05 rats. The 3rd principal strain (mean and 5th percentile) relative percentage differences were found to be 12.28% and 35.23% for the MR04, and 10.31% and 11.05% for the MR05 rats, in which the glaucomatous rat eyes had higher magnitude strains. When the experimentally measured mean IOP values were applied to the glaucomatous rat eye models, these calculated relative percentage differences were increased. Moreover, when the strain patterns in the anterior ON were observed, larger strains were located in the inferior ON in both of the glaucomatous rat eyes. Thus, the localization of high strain patterns observed in this study for the glaucomatous eyes were similar to the healthy rat eyes, which were dominantly located at the inferior ON. However, the magnitudes of the principal strains in the glaucomatous rat eye anterior ON were elevated due to the geometrical differences caused by remodeling and damage during the early stages of the disease.

When drilling for oil or gas, wells are typically constructed using a conventional or telescopic well design. After a section of the well has been drilled, a steel casing (or liner) is inserted into the hole preventing the collapse of the hole. The next well section has a smaller diameter as it’s casing must pass through the previously installed casing. This process leads to a stepwise reduction of the well diameter which, especially in deep or complicated wells, restricts the maximum production rate of oil and gas.

Mono-diameter technology utilizes casings which are plastically deformed after they have been placed in the well. This plastic deformation is done by pulling a conically shaped tool, known as the cone, through the newly installed casing. The plastic deformation increases the diameter of the new casing to (nearly) the same as that of the previous casing, therefore the well diameter no longer decreases with every new section.

The expansion requires a force in the order of 1000-2500[kN]. The work done by this force leads to high local heat generation due to friction and plastic deformation. This heat, poses a risk for the expansion process as the lubricant (RPSLF) decomposes above 250[C]. Decomposition of the lubricant leads to an increase of the friction, inducing more heat release and further decomposition of the lubricant. The expansion force may then exceed the pulling capacity of the drill rig or strength of the drill string, leaving the cone stuck in the well.

Previous research provides the distribution of pressure on the contact surface of the cone, the strain distribution inside the liner and the temperature dependent friction coefficient of the lubricant, by combining these the frictional heat is calculated. Heat generation from plastic deformation is a complex phenomenon
especially at low strain (-rates). The Taylor-Quinney coefficient defines the ratio between the work done on a material and the heat generated. A strain-dependent model for the Taylor-Quinney coefficient, developed by Zehnder, is used to determine the heat release from plastic deformation.

A numerical heat transfer model is built in Matlab, based on the finite volume method. The model uses a mesh based on skewed quadrilateral cells. Numerical stability of the model is verified for the cell size, time step and time integration method. Movement of the cone and the plastic deformation of the casing are modeled by taking a reference frame fixed relative to the motion of the cone and adding a ”convective” term inside the liner. Heat transfer phenomena at all boundaries are investigated using thermal resistance models.

A series of experiments is executed to verify the numerical model. The
experiments consist of full-scale expansion test using a cone equipped with 30 thermocouples placed just below the contact surface. Additionally also the temperature of the liner, expansion speed and expansion force are measured and recorded.

Comparison of the experimental and numerical results leads to the observation that the pressure profile determined in previous work is likely valid at the first onset of expansion. Over time, the forming of a lubricant film however leads to the re-distribution of roughly 20% of the force from the rear of the cone to the front. When the pressure profile is corrected for this effect; the temperatures inside the cone, temperature of the liner, expansion force and overall heat balance show a good match between the numerical and experimental results with an error of around 5%.

From the heat balance based on the experimental results, it follows that between 54% - 60% of the work done on the system is converted into heat. As all work done in the form of friction is converted into heat the remaining energy must be lost in the work done to plastically deform the casing, this provides indirect evidence for the validity of the Zehndermodel.

The validated numerical model is used to simulate a reference case field expansion, the maximum contact temperature here is 164.4[C]. This value is well below the lubricant decomposition temperature of 250[C], which leads to the conclusion that the process is safe and the expansion speed could even be increased from a thermal point of view.