TU Delft Repository

A two degree of freedom mass on a moving belt system has been considered to study the effect of friction-induced oscillations, due to nonlinear contact properties and external excitation, on friction modulation. Both tangential and normal excitation are present and the Hertz-Damp model governs the normal contact. The combined presence of the normal-tangential coupling through friction and of the external excitation, results in a parametric excitation and triggers friction-induced oscillations. Using a numerical analysis, the occurrence of such oscillations is explained through the inspection of the friction force versus relative velocity plots, which indicate the presence of a negative damping effect in the tangential direction, despite considering Amontons-Coulomb law. Hence, a linearized stability analysis of the steady sliding state, by taking advantage of the Method of Direct Separation of Motion, is employed to predict the bifurcation point as function of system parameters. It is shown that the linearized stability analysis provides a good qualitative agreement for the occurrence of the friction-induced oscillations for the investigated system, while the quantitative match varies depending on the system parameters and their values. Lastly, the effect of the observed friction-induced oscillations on the friction modulation is studied. Through a numerical analysis, a significant degree of scatteredness in friction force modulation is observed. Such scatteredness is significantly linked to the emergence of friction-induced oscillations, and it also depends on the averaging procedure used to quantify the effective friction reduction.

This paper studies the underwater sound and seabed vibrations generated from pile installation via axial and/or torsional vibrations, namely the "Gentle Driving of Piles" (GDP) method. A non-linear pile-soil-water model is utilized in this numerical study, where the pile vibrations and the resulting fluid-soil wave motion are analyzed. A semi-analytical finite element approach is used for pile-soil-water modelling and the pile-soil interaction is based on Coulomb friction enhanced with a memory mechanism. The comparison between classical axial vibratory driving and GDP is considered, investigating the effect of torsion in noise abatement as well as the presence of super-harmonic resonance-like phenomena.

As demand for high-bandwidth data transmission continues to increase, future satellite constellations can leverage the benefits of free space optical communication, which provides significant advantages compared to traditional radio frequency systems. Despite the development of satellite laser communication terminals (LCTs) in recent years, one major challenge remains; coupling the incoming signal into an optical fiber. In addition, most terminals use intensity modulation to encode data, which is limited in its ability to reach high data rates. So-called coherent modulation schemes offer superior performance but are not widely implemented in satellite LCT’s yet. A system that avoids fiber coupling while using coherent modulation could simplify designs, reduce complexity, and improve performance. This thesis presents the design, implementation, and evaluation of such a coherent free space optical detection system. Differential Phase Shift Keying (DPSK) was chosen as the modulation scheme due to its balance of power efficiency and implementation simplicity, delivering performance comparable to other coherent schemes with a less complex receiver architecture. The system was implemented using bulk optics and tested in a laboratory environment. A Delay Line Interferometer (DLI) was used for DPSK demodulation. The system successfully achieved a data rate of 100 [Mbit/s], demonstrating the feasibility of DPSK-based coherent free space detection. Some performance limitations were identified, with DLI instability emerging as the most notable, which is primarily caused by the long length required for this data rate. This instability resulted in intermittent bit error rate values exceeding the required threshold. These findings show that DPSK demodulation using bulk optics is favored toward higher data rates, and thus shorter delay lines. Recommendations for future work would be to operate at a higher data rate, and implement active stabilization for operational systems.

This research explores the relationship between industrial heritage and human well-being in the Waterdriehoek region of the Netherlands. It is focusing on the steel factory buildings in Alblasserdam. As many industrial structures from the late 19th and early 20th centuries face vacancy, the challenge of revitalizing these sites while addressing environmental and health concerns is crucial. Using a qualitative approach, the study combines desk research with a case study of the steel factory to assess its architectural qualities and impact on human well-being. Key questions investigate the preservation of industrial architectural values, the coexistence of heritage and residentials, and design strategies that promote well-being. Findings indicate that while the factory's features, such as natural light and spaciousness, enhance user well-being, challenges like pollution and limited green spaces remain. The research emphasises the importance of a comprehensive design approach, argues for strategies that integrate social, natural, and evidence-based elements. This approach aims to connect historical industrial use with future community needs, ultimately fostering well-being in revitalized areas.

The debate on climate risk labels in the Dutch housing market is gaining momentum, with opinions divided on their potential benefits and drawbacks. This thesis delves into the impact of flood risk labels on the housing market, focusing on residential real estate owned by professional investors. By adopting an investor's perspective, the study examines the implications of various flood risks, including those from main water systems, regional areas, and heavy rainfall. The research design incorporates a literature review, a questionnaire, and an expert discussion to validate the findings. The literature review explores the investment landscape in the Netherlands, existing labels in real estate, and sustainability reporting. The empirical research involves a questionnaire distributed to professional investors, followed by an expert discussion to validate the results. The study aims to understand how flood risk labels influence investment strategies and climate mitigation efforts. The findings reveal that flood risk labels somewhat benefit the decision-making process of professional real estate investors in the Netherlands. Investors consider flood risk labels as a valuable tool for risk reporting and guiding investment decisions in the face of climate change. The study contributes to the ongoing discussion on the necessity and design of climate risk labels, providing insights into their potential to improve housing valuations and investment strategies.