119092 research outputs found
Sort by
Inchworm-like Robot Locomotion using Off-the-Shelf 3D-printable Anisotropic Friction Pads
No full textThe paper reports on the experimental validation of combining inchworm-like locomotion with snake-like scales in anisotropic friction pads. The concept is demonstrated with a developed fully 3D-printable robot with four degrees of freedom. The real locomotion performance is evaluated for three different types of locomotion approaches in five terrain settings using achieved average locomotion speed and cost of transport. Suggested by measured properties, the proposed approach is capable of locomoting on the surfaces with sufficient surface friction difference using pad only and up to slope surface when combining the pads and body
Ermüdungsfestigkeit von Schraubendruckfedern - Vergleich der Berechnung nach DIN EN 13906-1 und der Richtlinie des Forschungskuratoriums Maschinenbau (FKM) „Rechnerischer Festigkeitsnachweis für Federn und Federelemente“
No full textDer Lebensdauernachweis von zyklisch beanspruchten Schraubendruckfedern erfolgt zurzeit mithilfe von Goodman-Diagrammen der DIN EN 13906-1. Eine Auslegung gemäß der Richtlinie des Forschungskuratoriums Maschinenbau (FKM) „Rechnerischer Festigkeitsnachweis für Maschinenbauteile“ kann aufgrund zu hoher Zugfestigkeiten der Federstähle nicht erfolgen. Im Rahmen des durch die Industrielle Gemeinschaftsforschung (IGF) geförderten und 2017 abgeschlossenen Forschungsprojekts mit der Nummer 18495 BG, wurde an der TU Darmstadt und der TU Ilmenau ein Nachweisverfahren in Anlehnung an die bestehende Richtlinie des Forschungskuratoriums Maschinenbau entwickelt, welches die federspezifischen Anforderungen berücksichtigt. In der vorliegenden Publikation wird der Berechnungsalgorithmus der neuen Richtlinie des Forschungskuratoriums Maschinenbau „Rechnerischer Festigkeitsnachweis für Federn und Federelemente“ dem Verfahren nach DIN EN 13906-1 gegenübergestellt und die Berechnungsergebnisse experimentellen Ergebnissen gegenübergestellt
Computing Mass Transfer at Deformable Bubbles for High Schmidt Numbers
No full textThe occurrence of extremely thin liquid‐sided concentration boundary layers at bubble or droplet interfaces for realistic, i.e., high Schmidt numbers is a severe obstacle for the numerical simulation of mass transfer processes in gas‐liquid systems. This contribution provides a survey of different approaches to overcome this problem, with the main emphasis put on the approach introduced and further developed by the authors. This approach employs a nonlinear flux computation and is based on the modeling of subgrid‐scale concentration profiles. Based on the latest developments, recommendations for future research are also provided
Autonomous atomic Hamiltonian construction and active sampling of X-ray absorption spectroscopy by adversarial Bayesian optimization
No full textX-ray absorption spectroscopy (XAS) is a well-established method for in-depth characterization of electronic structure. In practice hundreds of energy-points should be sampled during the measurements, and most of them are redundant. Additionally, it is also tedious to estimate reasonable parameters in the atomic Hamiltonians for mechanistic understanding. We implement an Adversarial Bayesian optimization (ABO) algorithm comprising two coupled BOs to automatically fit the many-body model Hamiltonians and to sample effectively based on active learning (AL). Taking NiO as an example, we find that less than 30 sampling points are sufficient to recover the complete XAS with the corresponding crystal field and charge transfer models, which can be selected based on intuitive hypothesis learning. Further applications on the experimental XAS spectra reveal that less than 80 sampling points give reasonable XAS and reliable atomic model parameters. Our ABO algorithm has a great potential for future applications on automated physics-driven XAS analysis and AL sampling
On a simple nonlinear system with circulatory forces
No full textSelf‐excited vibrations in mechanical system have been always gathering attention since being problematic for various applications, including brake squeal, aerodynamic flutter, machining chatter, and galloping transmission lines, or in some cases beneficial as in some musical instruments (ex. violin) or resonant MEMS. These vibrations can have different origins, such as ‘negative damping’ (such as in the classical Van der Pol oscillator) and/or circulatory forces (i.e. ‘follower forces’, non‐conservative positional forces). Both the negative damping and the circulatory forces can have different physical origins. It is well known that frictional forces generated between bodies in sliding contact can generate circulatory terms as well as damping and other types of forces. In particular, if one of two bodies in frictional contact moves with a constant speed or angular velocity, the other one being capable to oscillate, this implies an energy source for the oscillating part of the system. This has been identified as the cause for many self‐excited vibrations. In this presentation a very simple nonlinear two‐degree‐of‐freedom system of this general type is examined in some detail. It has recently been proposed in the literature as a paradigm for frictionally generated circulatory forces, for which the equations of motion can be derived from first principles. Other related systems have been presented in the literature before, but this newer system seems to be much simpler than the earlier ones and presents a great wealth of dynamic behavior. The nonlinear equations of motion of this 2‐DoF system always have the trivial solution and, depending on the system's parameters, also non‐trivial stationary solutions. The stability of the different stationary solutions is discussed in some detail. It was interesting to note that the increase of the friction parameter drives the system towards instability. This does however not happen, if the stiffness of both springs are identical, which practically can't be guaranteed
Investigation of the temperature‐dependent precompaction and flow behavior of hot mix asphalt
No full textThe flow behavior and precompaction resistance were investigated for the first time as part of this study. New laboratory methods were developed and applied for this purpose, some of which were based on already established methods. In order to evaluate the influence of temperature on the paving behavior of the asphalt paver, the flow behavior and precompaction resistance were investigated for three selected asphalt mixes (AC 11 DS, SMA 11 DS, AC 16 BS). The temperature was varied in three steps (130°C, 160°C, and 190°C). An extensive literature review of possible laboratory tests was conducted, which concluded that static compaction and the funnel fall test are suitable for investigating the corresponding properties of the asphalt mixes. The results showed that the bulk density of a loose fill asphalt mix is significantly dependent on temperature. Higher temperatures result in higher poured density due to the thermoviscosity of the bitumen, specifically, the viscous τ visc and cohesive τ c resistance components. Considering the performed laboratory tests, this phenomenon results in the loose fill of all tested asphalt mixes having a lower precompaction resistance at lower temperatures. In addition, the influence of temperature on the flow behavior and thus the internal friction of the asphalt mixes was demonstrated. Higher test temperatures resulted in a substantial reduction in flow time up to 225% and thus significantly improved flow behavior
Minimizing stress concentrations through material optimization with grayscale vat photopolymerization
No full textStructural optimization plays a crucial role in engineering by enhancing stability, minimizing stress concentrations, and improving material efficiency. Additive manufacturing, particularly vat photopolymerization with grayscale-masked stereolithography (gMSLA), provides new opportunities for optimizing material property distributions to achieve superior mechanical performance. This study proposes an optimization framework that adjusts grayscale levels in 3D printing to control material properties and mitigate stress peaks exceeding yield stress. This approach integrates finite element analysis with a gradient-based optimization algorithm to optimize material property distributions, enhancing structural integrity. The optimized grayscale distributions are then utilized to fabricate components via gMSLA, and experimental validation confirms the effectiveness of the proposed method in reducing plastic deformation and improving structural performance. The results demonstrate the potential of grayscale optimization in additive manufacturing for producing lightweight, high-performance structures
The Sensitivity of Muscle Activity to Magnitude, Duration and Timing of Small Plantarflexion Torque Pulses During Walking
No full textSmall perturbations can modulate gait characteristics and therefore have potential as a gait therapy for aged or clinical populations. To understand how the neuro-musculoskeletal system interacts with small perturbations, we investigated the response and sensitivity of different muscles activities to the torque pulse characteristics. We explored three pulse characteristics: 1) onset timing, 2) duration, and 3) magnitude. Electromyography (EMG) in five leg muscles showed how muscles activities changed depending on the perturbation characteristics. Six participants (four men and two women) walked on a treadmill at their preferred speed while wearing Bowden cable ankle exoskeletons on both legs. The exoskeleton applied Trapezoidal torque pulses with varying magnitudes and durations at five different gait cycle timings. EMG signals from the Tibialis Anterior, Gastrocnemius Medialis and Lateralis, Soleus, and Rectus Femoris muscles were collected. We calculated the coefficient of determination (R²) between EMG envelopes of perturbed and unperturbed strides to assess muscle response. Results indicated that torque pulse magnitude are more likely to significantly change EMG envelope of strides compared to pulse duration. Also, we observed that muscles show less change in activity, when the pulses are applied at push-off
Vorträge zum 3. Darmstadt-Berliner Baurechts-Kolloquium am 20. Oktober 2000 an der TU Darmstadt
No full textMit dem Mitteilungsheft Nr. 54 publizieren das Institut und die Versuchsanstalt für Geotechnik der Technischen Universität Darmstadt die Beiträge zum 3. Darmstadt-Berliner Baurechts-Kolloquium, das in interdisziplinärer Zusammenarbeit vom Institut für Deutsches und Internationales Baurecht e.V. an der Humboldt-Universität zu Berlin und dem Institut und der Versuchsanstalt für Geotechnik der Technischen Universität Darmstadt veranstaltet wird.
Die Themenschwerpunkte der abwechselnd in Darmstadt und in Berlin stattfindenden Baurechts-Kolloquien reflektieren die Intention der Veranstaltung, den vielfältigen Anforderungen der Investoren, der Architekten und Consultants, der Bauausführenden und Bauüberwachenden und der Juristen durch einen gemeinsamen Wissens-, Meinungs- und Erfahrungsaustausch gerecht zu werden
On the Role of Hierarchies, Abstractions, and Representations of Dynamics in Animal and Machine Learning
No full textHierarchies, abstractions, and representations of dynamics (HARD) are ubiquitous, both in real-world tasks and in animal neural architectures. This suggests HARD have significant potential to improve sample efficiency, safety, and resilience compared to modern AI trends, which have largely departed from the biologically plausible in favor of architectures that can better leverage massive-scale data and computation. We investigate HARD with a focus on the role of internal models in the form of oscillators, both based on explicit decentralized oscillators and in a fully data driven case