In a hydrodynamic journal bearing, the lubricant is pressurized by the relative movement of the bearing surfaces, creating a load-carrying capacity. The load-carrying capacity can be increased by using a lubricant with higher viscosity, at the cost of increased friction. A proposed method to increase the maximum load-carrying capacity, while not increasing the friction at lower loads (or at higher speeds), is by using magnetorheological (MR) fluid as lubricant and electromagnets to generate a magnetic field. MR fluid consists of a carrier fluid with micron-sized magnetic particles suspended. Under the influence of an external magnetic field, the viscosity of the fluid increases as the particles form chain-like structures. Using electromagnets, the magnetic field strength can be adjusted based on the operating conditions of the bearing and the bearing can be semi-actively controlled. The objective of this thesis is to create a visual demonstrator setup, intended for educational purposes, that can be used to investigate the pressure distribution and generated forces in a hydrodynamic half journal bearing using MR fluid and electromagnets. Furthermore, the research objective is to increase the maximum load capacity for a specified minimum film thickness, while not increasing the friction in the hydrodynamic lubrication regime. The test setup was based on an existing setup made by GUNT which is able to show the pressure distribution in a half journal bearing using pressure tubes for various eccentricity ratios. Adaptations to this setup were made to measure the generated forces (horizontal force, vertical force and friction force, defined as the frictional moment divided by the radius of the bearing) and to implement an electromagnet. First, experiments using hydraulic oil were performed to test and improve the performance of the setup. Afterwards, experiments using MR fluid were performed with varying magnetic field strengths. Furthermore, a numerical model based on the two-dimensional Reynolds equation was created and validated with the experimental results. Both the numerical and experimental results showed comparable trends of increasing pressure, horizontal force and vertical force, meaning an increasing load capacity, for increasing eccentricity ratio and applied current. The numerical friction force also increased with increasing eccentricity ratio and applied current, while the experimental friction force only increased with increasing applied current and did not show a clear trend with increasing eccentricity ratio. The magnitude of the forces differed significantly between the experimental and numerical results, where the largest differences were observed for the vertical force and the friction force. Many plausible causes for the differences are identified, such as bearing tolerances, uncertainties in eccentricity and modeling simplifications. A combination of these causes is believed to lead to the observed differences. The increase in pressure, horizontal force and vertical force due to an increase in applied current was found to be much smaller experimentally than numerically. This was thought to be caused by a larger temperature increase in the experimental tests than was modeled and by simplifications used in the numerical model such as neglecting the shearthinning characteristics of MR fluids. The friction force differed even more significantly between the numerical and experimental results. Additionally, this is caused by the small magnitude of the friction force in combination with a test setup that is not accurate enough to measure small forces consistently. The created setup can show the change in pressure distribution when the applied current or eccentricity is changed. It therefore serves as a visual demonstrator setup for an MR lubricated hydrodynamic half journal bearing which can be used for educational purposes. However, demonstrator performance was found to be far from ideal as the changes in fluid column height were very slow because of the high MR fluid viscosity. Performance can potentially be improved by using a different or diluted MR fluid. Despite the large differences between the numerical and experimental results, both can be used to display the potential of semi-active control using MR fluid and electromagnets. It is shown that the maximum load capacity can be increased while not increasing the friction coefficient in the hydrodynamic lubrication regime. Several recommendations have been made for changes to the demonstrator setup to improve performance while keeping the setup simple and elegant. The main recommendations include improving the bearing tolerances, testing with a different or diluted MR fluid, implementing capacitive distance sensors and performing experiments at a more consistent ambient temperature.

Current service and installation activities for offshore wind turbines are carried out by jack-up vessels, which eliminate wave disturbances to a large extent. The use of these vessels imposes several disadvantages, including high operational costs and the limitation of operating in restricted water depths. An alternative is a crane mounted on a floating vessel (monohull), which is quicker in operation and multi-deployable. With these vessels, however, a motion compensator is needed to eliminate most of the hydrodynamic disturbances. The purpose of this graduation assignment is to develop a concept design for a passive motion compensator (PMC) to isolate the vessel motion from the payload.

This goal is achieved by the implementation of a multi-objective optimization algorithm based on genetic programming (GP) that constructs a two-dimensional PMC based on the principle of quasi-zero stiffness. The GP employs a set of genetic operators to explore the design space in terms of topology and design variables, which effectively mimics Darwin’s Theory of Evolution. The better a mechanism performs, the higher the fitness, and thus the higher the chance this design appear in future generations.

Each design is a composition of cylinders and nodes that are assembled into a mechanism. During the fitness evaluation, all mechanisms are examined by a nonlinear finite element method to extract the force-displacement relations. The arc-length control method is used due to the large displacements and rotations of the members in the mechanism, whereby both the nodal displacement vector and external load vector are varied to follow an equilibrium path in an incremental-iterative way. To provide sufficient support to the payload, the mechanism is prestressed, which is applied by using the arc-length procedure as well.

Static and dynamic results show that the GP is suitable for constructing a high-level planar QZS mechanism for the intended application in various sea states. From multiple runs, it can be concluded that the optimizer generally produces designs with the same topology. Dynamic analyses in the time domain show that motions are effectively mitigated in the horizontal and vertical directions for the chosen designs. In addition, analysis in the frequency domain shows that the mechanisms effectively attenuate motions in the frequencies of interest.

TransPerineal Laser Ablation (TPLA) is a novel, minimally invasive procedure that uses accurately positioned needles through which optical fibres are inserted to ablate malignant prostate tissue, demonstrating minimal side effects in early studies. Accurate needle placement and guidance can be affected by many factors such as needle buckling, imaging modality, and needle deflection. Using the self-propelling mechanism seen in the ovipositor of parasitoid wasps, the risk of buckling can be reduced and tissue damage can be minimised. Drawing inspiration from this principle, we created a stationary, MR-conditional 3D printed device with integrated laser functionality that can propel a needle system through stationary, human-like tissue. Our results show that needle traversal through multiple gelatin phantoms (up to 15 wt%) is possible. The needle (bundle) can move through these phantoms without buckling, due to its near-zero (max 0.28 N) net put force. The propelled needle (bundle) has an outer diameter of 1.2 mm, which includes a centrally located needle through which the optical fibre, used for laser ablation, can be inserted. Our wasp-inspired needle design and prototype narrow the gap to the clinical implementation of wasp-inspired needles for MRI-guided TPLA. Moreover, with minimal design changes, our device may serve as a versatile platform for applications beyond its intended purpose of TPLA, such as camera positioning, drug delivery, tissue engineering, and tissue extraction.

Individuals suffering from neuromuscular conditions, such as Duchenne muscular dystrophy (DMD), experience a progressive weakening of muscles. During the progression, the affected patients require supporting devices like orthoses or exoskeletons to perform their daily activities. Although immense efforts are put into the development of exoskeletons, due to the challenge involved in balancing the weight on the hand, where the torque at the wrist changes with the position of the hand, there are limited wrist support devices available. Existing solutions either rely on rigid body mechanisms or active power sources, which come with drawbacks like bulkiness and discomfort. This research introduces an innovative approach to passively counterbalance hand weight using a simplified torque profile for a single degree of freedom in hand movement, namely flexion and extension. By employing parametric optimization, a compliant mechanism has been developed that can compensate for the weight of the hand against gravity. The resultant compliant mechanism design is compact, lightweight, and safe, rendering it an optimal choice for supporting the wrist’s degrees of freedom and for the application of the device. Through the experimental validation of the model, the results are interpreted as the mechanism’s usefulness in wrist flexion and extension support. In short, this study underscores the utility of employing compliant mechanisms in wrist support orthoses, particularly for individuals with neuromuscular conditions like DMD.

Neuromuscular diseases often result in elevated passive joint impedance (PJI), impacting the daily lives of affected individuals. To be able to apply assistive devices that compensate for PJI, it is essential to identify the PJI correctly. This study aims to identify and model the PJI of the elbow joint, to improve the control of force-based controlled active-assistance exoskeleton devices by distinguishing the voluntary from the passive forces. We used an elbow device to measure the PJI in twelve healthy males with the shoulder abducted at a 90˚ angle. The study investigates both static and dynamic conditions, encompassing various contraction velocities (≤ 0.20 rad/s) and shoulder flexion positions (0˚ and ±45˚). The analysis estimates the hysteresis, equilibrium position, and elastic property. Subsequently, based on the average elbow PJI, we developed a regression model, with the statistical analysis revealing no significant differences between the conditions, except for the observed hysteresis under varying velocities. Based on the tested conditions, the findings indicate that a single low-velocity dynamic measurement can serve as the basis for deriving a general elbow PJI regression model.

In the engineering industry, all structural parts have to be designed as efficient and lightweight as possible. Traditionally, the design process has been carried out through manual design iterations, which can be time-consuming and require significant engineering expertise. Over the last decades however, several computational design techniques like Topology Optimization and Generative Design have been developed to support engineers in the structural part design process. Even though these techniques can have a positive influence on the design process, they both also have their downsides. Topology Optimization only gives a single result that is often a local optimum, influenced by boundary conditions and numerical settings. Commercial Generative Design tools explore multiple design options in a single run using AI algorithms, but need cloud-based systems to carry out their demanding simulations which still take several hours per run. It is however expected that a combination of the two, a Topology Optimization based Generative Design approach in the form of an auxiliary tool, has potential to improve the early stages of the design process even more. With such a design approach, multiple design solutions are explored quickly to study the effect of boundary conditions or numerical settings. This can help designers by giving direction and insight in trade-offs between multiple objectives, early on in the design process when design decisions still have the highest impact.

The goal for this research was therefore to research the effect of such a Topology Optimization based Generative Design approach on the design performance and experience. In order to do so, a robust and user-friendly TOP-GD tool was created. In this tool, multiple design solutions are explored quickly by implementing a batch-run setup that varies several chosen parameters, without needing to manually run several optimizations consecutively. Calculations are done with a simple TO script using coarse geometries, and without taking into account manufacturing methods yet. This asks for less demanding, detailed and complicated calculations than AI-based Generative Design tools currently offer, while at the same time moving from a single TO result to generating a range of candidate solutions. A lot of effort was put in the user-friendliness of the TOP-GD tool, enabling an easy workflow for the setup of design problems and a clear presentation of the results by means of a simple GUI.

The use of the TOP-GD tool in the design process was evaluated in an experiment, where it was compared with a more simple TO tool and a basic manual design approach using just pen and paper. This was done by giving the participants of the experiments three simple design assignments, that they had to carry out using each of the design approaches one by one. Evaluation of the approaches was done by comparing the design performance, and assessing the design experience with a survey and using Eye-tracking techniques.

The results of this experiment did not show enough evidence to conclude that the different design approaches had an effect on the design performance for the simple assignments executed during the experiment. However, the results of the survey show a clear positive impact of both the TO tools on the design experience, compared to manually designing. Furthermore, the TOP-GD tool has the largest positive impact on the design experience and its use in the design process is considered a big improvement, especially in quickly exploring new design directions and creating overview. This confirms the expectation that a Topology Optimization based Generative Design approach has a positive effect on the early stages of the design process. The differences found with Eye-tracking between the TO tools support this, although a more extensive experiment should be done to convincingly confirm this conclusion.

A growing energy demand has sparked interest into harvesting energy from the human body. Often, a rotational proof mass is used to harness energy for a wearable from kinetic motion of its user. The addition of a spring has the potential to significantly increase efficiency for these low-power rotational energy harvesters. In this research a system characterisation is performed from which a dimensionless ratio is formulated to determine optimal spring stiffness for maximisation of average power output as a function of harvester design parameters and excitation inputs. Creating a system that is optimized for the entirety of its operational range rather than for one specific excitation input. Implementation is investigated in the field of horology, where rotational energy harvesters are widely implemented. To increase harvesting efficiency of existing rotational energy harvesters without requiring significant design alterations a compliant design is proposed, prototyped and tested.

Flexure mechanisms are widely utilized in precision mechanisms, but their practical use is limited by three major factors, namely restricted range of motion, parasitic motion, and significant reduction in support stiffness when deflected. To address this limitation, in this research the potential of variable thickness flexures in minimizing the aforementioned issues is evaluated. Two novel parametrizations are utilized to optimize these variable thickness flexures, which are then compared to their commonly used constant thickness counterparts. Furthermore, initially curved flexures have been found to be promising in optimizing mechanisms with high performance in terms of parasitic motion and stiffness tuning. Three novel designs are proposed and optimized in this research for improved performance. As variable thickness showed promising results, these newly designed mechanisms are further optimized by incorporating variable thickness into the initially curved flexure mechanisms. The outcomes of this study demonstrate a significant enhancement in terms of support stiffness and range of motion without compromising other important factors.

In conventional compressor technology, high pressure ratios are often achieved by multiple, successive compression stages. This is done to avoid high temperatures due to the adiabatic nature of most compression processes which deteriorates the working of oil lubrication. The aim of this work is to reduce a conventional four-stage system to only two stages as this may improve the size and expenses of the system. This goal combined with a long desired lifetime, makes that a compressor is developed that operates based on gas bearing technology.

The design is focused on two main subjects. Firstly, the load capacity of the gas bearings is significantly lower than oil lubricated bearings due to the reduced viscosity. To avoid mechanical contact and wear of the components this has been thoroughly analysed using finite element methods. The oscillating nature of the loads in the system enhances the squeeze effect from the Reynolds equation. Secondly, the sealing function of gas bearings opposing internal leakage is evaluated carefully to obtain a desired efficiency. Based on these simulations, the mechanical design of the compressor is optimized to improve the manufacturing of the compressor components.

This report is written for the thesis of my master Mechanical Engineering that was conducted at the department Precision and Microsystems Engineering of the Delft University of Technology. The goal of the project was to design a compliant hipback support of an exoskeleton while researching how to achieve desired directional compliance on this application. This work starts with an introduction to exoskeletons and explaining their working principles. The problem is that the reduction of range of motion for wearing an exoskeleton reduces the adoption of exoskeletons in industry. The objective of this study was to solve this by creating a hipback support with compliant behaviour in torsion and lateral bending while remaining stiff in the supporting forward bending direction. For inspiration, the state of the art of current hipback supports and research projects was reviewed. Also, the characterization methods of compliant mechanisms were reviewed for inspiration, to come up with a suitable design method for developing a compliant structure for a hipback support. By tuning stiffness of the structure in distinct directions, a conventional synthesis method for compliant mechanisms could be applied, namely the Freedom and Constraint Topologies method. This was used to come up with a preliminary design. This design was extended to improve stiffness behaviour for coupled motions by researching how to change stiffness on demand. The only categories to change stiffness are shape, material, prestress and boundary condition. For each category, a promising highlevel design was worked out with improved stiffness behaviour for coupled motions. To generate an even more satisfying solution, optimization of the beam shape was applied to handle the defined rather complex kinetostatic task and to develop a lightweight structure. The objective function was to reach specified deflections where shaperelated parameters are optimized. These parameters were the spine shape of the beam, the crosssection and orientation of the crosssection. To generate a design, a selfdeveloped optimizer using beam modelling was extended and applied. The extensions were to optimize a doubleclamped beam that was loaded in the middle point and optimizing for angular deformations as a set objective function. This extended optimizer generated the final design which was a thin rectangularshaped beam with threedimensional curves. This design was not straightforward to fabricate into a prototype. Multiple manufacturing methods were evaluated and one final method was selected to fabricate a close approximation of the final design. This final manufacturing method was to produce the prototype by roll bending and manually applying a twist on a curved lasercut strip which was extracted from flattening of the spatial shape. This prototype was verified by simulations and experiments. Simulation tests were run on an original design of the back support and compared with the new optimized shape based on the requirements. The results, for similar loadings and material, are 27 times more lateral flexibility, 1.25 more torsional flexibility and a design that is four times lighter in comparison to the original design. The original relative stiffness of 1 to 1 for forward relative to lateral bending improved to 2 to 1. An important remark to note is that the beam model generated a thin section which was less suitable for 1D beam modelling of the implemented FEM. Creating an optimizer based on 2D shell modelling code might give more accurate results and can be considered for future work.