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Relevance of the Basset history term for Lagrangian particle dynamics
No full textThe movement of small but finite spherical particles in a fluid can be described by the Maxey-Riley equation (MRE) if they are too large to be considered passive tracers. The MRE contains an integral "history term" modeling wake effects, which causes the force acting on a particle at some given time to depend on its full past trajectory. The history term causes complications in the numerical solution of the MRE and is therefore often neglected, despite both numerical and experimental evidence that its effects are generally not negligible. By numerically computing trajectories with and without the history term of a large number of particles in different flow fields, we investigate its impact on the large-scale Lagrangian dynamics of simulated particles. We show that for moderate to large Stokes numbers, ignoring the history term leads to significant differences in clustering patterns. Furthermore, we compute finite-time Lyapunov exponents and show that, even for small particles, the differences in the resulting scalar field from ignoring the BHT can be significant, in particular if the underlying flow is turbulent
Sonic boom velocity and altitude sensitivity analysis of a hypersonic aircraft concept
No full textDuring the last decades there has been a renewed interest in the development of a new generation of supersonic aircraft for civil purposes with limited implications to the environment. However, the noise generated by supersonic aircraft during supersonic flight, commonly referred to as "sonic boom", still creates annoyance to community on the ground that prohibits supersonic overland flight. To prepare for the advent of a new generation of supersonic aircraft and to define new regulations for them, an increasing number of sonic boom studies is being published. This paper presents numerical simulations of the sonic boom of a hypersonic (Mach 5) aircraft concept during the full flight envelope, including a sensitivity analysis of the two parameters velocity and altitude. The extensive simulations characterize the sonic boom distribution on ground, which is usually referred to as "sonic boom carpet", caused by the aircraft for different speeds between Mach 1.2 and Mach 5.0, and for two altitudes of 11.3 km and 28.0 km above sea level. Different loudness metrics were calculated for the different flight conditions, including PLdB, ISBAP and SEL related metrics. The simulation approach is divided into two main regions. This approach is well understood and was validated during the three NASA Sonic Boom Prediction Workshop held between 2014 and 2021: The dual approach consists of (1) a near-field domain computed with Computational Fluid Dynamics (CFD) using a hybrid mesh and a Fluent solver based on ROE-FDS numerical scheme, and (2) a far-field propagation algorithm based on ray tracing and a nonlinear, one-dimensional shock wave propagation algorithm (Augmented Burgers Equation). The results highlight the differences in sonic boom behavior and loudness metrics due to Mach number and altitude variation. The propagation results are compared with the ones given by NASA's PCBoom software
Impact of surface treatments on the photocatalytic performance of anodic aluminum oxide templates
No full textNanostructured materials receive great interest nowadays due to their unique properties, increased surface areas, and superior performances with associated reduced material usage. However, directly nanostructuring functional materials themselves can be technologically challenging. Hence, nanostructured substrates such as anodic aluminum oxide (AAO) can serve as templates for depositing active materials. The templates’ chemical stability is crucial for accurately assessing functional materials. Since AAO structures incorporate electrolyte ions during anodization, their chemical stability is influenced by the subsequent processing after anodization. This work investigates the effect of various post-anodization modifications on the surface chemistry and photocatalytic performance of bare AAO structures. Treatments with H2O2 or H3PO4 can stabilize the photocatalytic performance of the AAO templates over consecutive measurements. XPS measurements indicate that such stabilization results from AAO surface chemistry alterations. Further, we explore the functionalization of these modified AAO templates with photocatalysts by atomic layer deposition. The photocatalytic performance of TiO2 as a chemically stable photocatalyst is not affected by the templates’ post-anodization treatment. In contrast, the performance of templates functionalized with Fe2O3 as an inherent chemically instable photocatalyst depends on the template stability. This work highlights the importance of chemically stable template materials for exploring the properties of new functional materials
Lern- und Arbeitsprozesse im Wandel: Transformation gewerblich-technischer Facharbeit und Berufsbildung
No full textDer vorliegende Sammelband dokumentiert die 23. gtw-Herbstkonferenz, die am 10. und 11. Oktober 2024 an der Universität Siegen stattfand. Unter dem Leitthema „Lern- und Arbeitsprozesse für die Transformation gewerblich-technischer Facharbeit" versammelt die Publikation über 20 wissenschaftliche Beiträge der gewerblich-technischen Wissenschaft und ihrer Didaktik (gtw), die sich mit den tiefgreifenden Wandlungsprozessen in der gewerblich-technischen Facharbeit, der Berufsbildung und der Lehrerbildung auseinandersetzen. Im Zentrum stehen Herausforderungen und Chancen, die u.a. durch Digitalisierung, Nachhaltigkeit und Künstliche Intelligenz entstehen - drei Megatrends, die die berufliche Bildung grundlegend verändern.
Die Beiträge spiegeln sowohl (berufs)wissenschaftliche Analysen als auch praxisorientierte Konzepte wider und sind in vier thematische Bereiche gegliedert: (1) Berufsgestaltung und Qualifizierungsansätze, (2) Nachhaltigkeit und Energiewende, (3) Digitale Transformation und (4) Bildungspersonal.
Der erste Bereich beleuchtet Strukturfragen der Berufsbildung, neue Berufslaufbahnkonzepte und Qualifizierungsansätze, etwa im Kontext der Metall- und Elektroberufe oder der Mikro- und Nanotechnologie. Der zweite Bereich widmet sich der beruflichen Bildung für nachhaltige Entwicklung (BBNE) und analysiert u.a. die Qualifizierungsanforderungen in der Batteriezellenproduktion. Im dritten Teil werden didaktische und organisationale Konzepte zur digitalen Transformation vorgestellt - mit Fokus auf KI-gestützte Lernumgebungen und deren Integration in Bildungssysteme. Im vierten Bereich rückt das Bildungspersonal in den Fokus, das als Schlüsselakteur der Transformation gilt.
Der Tagungsort Siegen - insbesondere der Campus Buschhütten - steht beispielhaft für innovative Lernorte, an denen Forschende, Lehrende und Lernende gemeinsam Transformationsprozesse gestalten. Die Publikation bietet fundierte Impulse zur Weiterentwicklung der beruflichen Bildung und versteht sich als Beitrag zur wissenschaftlichen und praktischen Diskussion im Feld der gewerblich-technischen Wissenschaften und ihre Didaktiken
Foresee: ML-driven, communication-efficient time-series forecasting
No full textIn the Internet of Things, a multitude of sensors continuously collect data and transmit it to the cloud for analysis. However, frequent transfer of measurements is impractical for battery-powered sensors due to the high energy-costs of wireless communication. Therefore, sensors often collect data and send it at periodic intervals, while a state-of-the-art cloud-based predictive model estimates intermediate values between transmissions. This paper introduces Foresee, which improves data quality on the cloud without additional communication overhead compared to periodic and model-drives approaches. Foresee makes local predictions on the sensor by employing a small, resource-efficient neural network. Upon detecting significant deviations between predicted and measured data, Foresee communicates these measurements to the cloud. Thus, Foresee notifies the cloud whenever predictions are difficult. On the cloud side, Foresee uses a state-of-the-art transformer model to make predictions between transmissions. Our results demonstrate the effectiveness of Foresee across different datasets. For instance, on the AlSolar dataset, with a prediction length of 48, we observe a 26% improvement in the Mean Absolute Error without any additional communication, compared to periodic communication every 39 timesteps. Additionally, Foresee achieves a 63% reduction in Mean Absolute Error compared to a model-driven approach with the same communication overhead
Feasibility study on ultrasonic-assisted processing techniques for the value-retention of hybrid thermoplastic–thermoset composites
No full textThe integration of high-performance thermoplastics in fiber-reinforced polymers with thermoset matrices offers the possibility of using existing manufacturing processes and at the same time incorporating the advantages of thermoplastics. These include higher fracture toughness, weldability and reprocessability. Among existing high-performance thermoplastics, polyetherimide (PEI) stands out due to its amorphous structure, which provides good compatibility with thermosets. This study investigates the integration of a PEI interlayer within carbon fiber-reinforced epoxy prepregs to evaluate the feasibility of value-retention and multiple circular use of hybrid thermoplastic–thermoset laminates via power ultrasonics. A novel ultrasonic-assisted separation method employing a cutting tool enabled controlled pre-crack initiation and propagation along the PEI interface, resulting in clean and repeatable separation. Subsequent displacement-controlled ultrasonic reconsolidation of the separated laminates, facilitated by a PEI film as energy director, led to uniform melt generation and a 55% increase in lap-shear strength compared to time-controlled reconsolidation experiments. Furthermore, double cantilever beam (DCB) testing revealed a 250% enhancement in the critical energy release rate (GI,C) for laminates with PEI interlayer, demonstrating significantly improved fracture toughness. These findings underscore the dual functionality of the PEI interlayer, not only as a toughening agent but also as an enabler for reprocessing and reusing by power ultrasonics. The demonstrated approach offers a compelling pathway for sustainable composite design, particularly for aerospace applications where mechanical performance and end-of-use circularity options are critical
Simulated ice loads on a ship propeller and comparison with full-scale measurements
No full textA methodology to better estimate the loads of ice acting on the propeller of a ship is developed. Based on measurements conducted in the North Pole region, an existing failure model for ice based on the Mohr–Coulomb nodal split approach is modified to better represent the lower strength of polar ice compared to laboratory ice. The modified material model for the sea ice is used to compute the propeller torque and a load spectrum for the propeller-ice interaction of the research ship S.A. Agulhas II. To this end, a floe-ice breaking simulation is used to estimate the size and shape of the ice cusps hitting the propeller of this ship. In the next step, a set of finite element simulations of the propeller-ice interaction utilizing the modified Mohr–Coulomb nodal split model is conducted. Based on this, the load spectrum is computed and compared with the measured torque on the propeller shaft of the S.A. Agulhas II. The successful reproduction shows the applicability of the approach to better estimate the loads exerted by the ice on the propeller
Effect of anion hydrophobicity on the oxidation of ferrocene-terminated monolayers
No full textSelf-assembled monolayers (SAMs) terminated with ferrocene ((Formula presented.)) moieties are a popular model system for electron transfer processes at solid-liquid interfaces. Numerous experimental studies have found a correlation between the hydrophobicity of anions in the electrolyte and the redox potential. In this computational study, the redox potential is calculated for various anion species and SAM configurations using classical molecular dynamics. Thermodynamic integration and the constrained charge method are used to determine the redox potential as the free energy change associated with electron transfers from the (Formula presented.) moieties to the electrodes. The results show the anticipated lower redox potentials for hydrophobic anions and allow the study of changes at the solid-liquid interface at the atomistic level
A workflow for designing stiffness-optimized structures in the context of additive manufacturing of endless fiber-reinforced composites
No full textThis paper investigates the interface between structural optimization for anisotropic materials and modern additive manufacturing methods by presenting and evaluating a workflow for the design of structures for fused filament fabrication using endless fiber-reinforced filament. The process chain consists of optimizing the material orientations and topology of the anisotropic structure simultaneously, non-planar slicing and load-oriented path planning for additive manufacturing. The design workflow is demonstrated using an academic example and validated by a more practical example including mounting regions for bolts and multiple load cases. The results expose requirements for additive manufacturing of continuously fiber-reinforced structures that have to be considered by the optimization process for narrowing the gap between optimization results and simulated performance of the manufactured parts. At the same time, the potential of the presented workflow for designing parts while taking manufacturability into account is demonstrated successfully
Adjoint-assisted robust shape optimization of an idealized arterial bypass graft using the FOSM method
No full textThis paper presents the shape optimization of an idealized arterial bypass graft under uncertainties. The underlying blood flow problem is numerically solved using computational fluid dynamics (CFD) simulations, able to account for mechanical hemolysis and non-Newtonian viscosity properties of blood. The employed hemolysis and non-Newtonian models utilize a set of parameters that are considered uncertain in this work. To this end, the optimization problem is rendered robust and targets the minimization of the first two statistical moments of a hemolysis index. The propagation of the uncertainties to the hemolysis index is done through the first-order second-moment method (FOSM). The necessary derivatives are computed by the adjoint method and finite differences. Several steady-state robust shape optimization simulations of the idealized bypass graft are presented. Selected optimized shapes are further assessed by means of additional fluid–structure interaction (FSI) simulations under unsteady conditions