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Numerical and physical robustness with respect to nodewise geometrical uncertainty in topology optimization
No full textDeterministic optimization applied to non-parametric optimization, such as topology, sizing, or shape optimization, may result in optimized designs that are highly mesh-dependent or correspond to a local minimum. Previous robust design optimization methods that consider global geometrical perturbations demonstrate the ability to suppress many local minima in the response function, and thereby, yield improved optimized designs. However, different mesh discretizations sometimes yield fundamentally different optimized designs that cannot be suppressed using global uncertainty formulations. Hence, a novel uncertainty measure is proposed, based on nodewise uncorrelated local geometric distributions. Firstly, the proposed approach employs a computationally efficient generalized first-order method, ensuring improved numerical mesh-independence of optimized designs. Secondly, the proposed method allows for a semi-intrusive implementation independent of the number of design variables and the design variable type. The proposed method is applied as a local uncertainty measure to various numerical examples addressing both numerical and physical geometrical robustness including the design of compliant hinge mechanisms, as well as stiffness- and stress-based optimization formulations
Bewertung von neuer Technik in der Mobilität am Beispiel autonomer Minibusse im ÖPNV ländlicher Räume
No full textMit dem autonomen Fahren im Straßenverkehr werden vielfältige Hoffnungen verbunden. Dazu gehören eine höhere Verkehrssicherheit, eine bessere Teilhabe von Menschen ohne Fahrerlaubnis, eine andersartige Nutzung der gewonnenen Zeit und eine Senkung der Kosten der motorisierten Fortbewegung. Für ländliche Räume besteht die Erwartung einer flexiblen Mobilität für Alle. Hinsichtlich der tatsächlichen Folgewirkungen des autonomen Fahrens existiert derzeit jedoch in vielfacher Hinsicht kein hinreichendes Orientierungswissen. Ziel der Ausarbeitung ist es, diesem Defizit zu begegnen, indem ein Verfahren genutzt wird, das frühzeitig Wissen in einer ganzheitlichen Bewertung für eine neue Technik in der Mobilität bereitstellt. Dabei sind neben der Feststellung des Stands der Technik und der Potenziale die Risiken und Nebenwirkungen des soziotechnischen Systems zu identifizieren. Bei der konkreten Anwendung des Verfahrens soll der Fokus auf fahrerlosen Minibussen im ÖPNV ländlicher Räume als ein möglicher Anwendungsfall der Technik liegen. Die zur methodologischen Herausforderung durchgeführte Recherche zu verfügbaren Lösungsansätzen liefert aus der Verkehrsplanung, der Technikfolgenabschätzung und der Technikbewertung heraus zwar kein direkt anwendbares Verfahren, aber hilfreiche theoretische Erkenntnisse. Diese führen zu einer eigenen stark strukturierten Vorgehensweise, die sich für die Bewertung einer Technik in der Mobilität eignet. Die Bearbeitungsphasen gliedern sich dazu in einen Scoping-Prozess, eine Definition des individuellen Zielsystems, eine Überprüfung der Einsatzbedingungen, eine Synthese zu potentiellen Einsatzszenarien sowie eine Analyse und umfassende Bewertung des soziotechnischen Systems. Die entscheidende Phase der Bewertung umfasst die Feststellung der individuellen Zielerreichung, das Verständnis des aktuellen Wirkungsgefüges und eine multiperspektivische Einordnung der Risiken. Bei der Anwendung des zuvor entwickelten Verfahrens wird unter Einsatz verschiedener Methoden auf das „Testzentrum für automatisiert verkehrende Busse im Kreis Herzogtum Lauenburg“ zugegriffen, was eine praktische Erprobung automatisierter Versuchsträger sowie eine Beteiligung von Stakeholdern, Nutzenden und der Bevölkerung ermöglicht. Im Ergebnis zeigt sich aus der Bewertung, dass durch einen Einsatz fahrerloser Fahrzeuge im ÖPNV die Herausforderungen der Mobilität der vielfältigen ländlichen Räume nicht grundsätzlich gelöst werden können. Die erhofft großen Potenziale fahrerloser Minibusse in Bezug auf Steigerung der Sicherheit, Kostenreduktion bei disperser Nachfrage und uneingeschränkte gesellschaftliche Teilhabe wirken derzeit für den betrachteten Anwendungsfall überbewertet. Aus der Anwendung der Risikoanalyse werden negative Folgen des fahrerlosen Fahrens erkennbar: Als potentielle Gefahren mit einem großen Schadensausmaß sind insbesondere Missbrauch oder Manipulation der Technologie, negative Umfeld-, Umwelt- und Gesundheitseffekte, fehlende Teilhabe sowie hohe Komplexität mit Störungsanfälligkeit und entsprechenden Folgen bei hoher technischer Abhängigkeit zu nennen. Es werden weitere konkrete Risiken identifiziert, die die gesellschaftliche Akzeptanz und die aktuelle Wahrnehmung der Menschen beeinflussen. Dabei kann über den neu entwickelten Ungerechtigkeitsfaktor zwischen objektiv ungerechten Risiken und subjektiv kritisch empfundenen Risiken differenziert werden. Allerdings wird auch deutlich, dass ein plötzlich auftretendes großes irreversibles Schadensausmaß durch fahrerloses Fahrens im Straßenverkehr bislang nicht erkennbar ist. Insgesamt zeigt sich, dass fahrerloses Fahren nicht grundsätzlich die Lösung im Sinne der definierten Ziele ist. Es sind die übergeordneten Fähigkeiten des Mobilitätssystems mit optimaler Integration und Vernetzung verschiedener Verkehrsmittel unter Berücksichtigung der individuellen Bedürfnisse im jeweiligen Raum zu betrachten. Dabei spielen Verlässlichkeit, räumliche und zeitliche Flexibilität bei kurzen Zugangswegen sowie einfache Handhabbarkeit und Verständlichkeit eine wichtige Rolle. Fahrerloses Fahren bedarf als ein möglicher Bestandteil der übergreifend zu gestaltenden Mobilität weiterer kritischer Betrachtung und Steuerung, damit es ganzheitlich positive Wirkungen entfaltet. Der Mehrwert dieses Verfahrens resultiert aus der Auflösung der Komplexität einer Technik im Steuerungs- und Kontrolldilemma unter der Produktion von strukturiertem Orientierungswissen. Es stellt sich ein umfassendes soziotechnisches Verständnis für das betrachtete System ein, das in einer Momentaufnahme eine realistische und ganzheitliche Sicht auf die Fähigkeiten und Risiken der Technik ermöglicht. Der gewählte Ansatz motiviert zur Verknüpfung verschiedener Methoden, die die Menschen mit ihren individuellen Bedürfnissen in den Mittelpunkt einer nachhaltigen Entwicklung der Technik stellen.There are many hopes associated with autonomous driving in road traffic. These include greater road safety, better participation of people without a driving licence, a different use of the time gained and a reduction in the costs of motorised transport. Flexible mobility for all is expected in rural areas. However, in many respects, there is currently insufficient information available on the specific consequences of autonomous driving. The aim of this paper is to counter this deficit by using a procedure that provides knowledge at an early stage in a holistic assessment of a new mobility technology. In addition to determining the current state of the technology and its potential, the risks and collateral effects of the socio-technical system are to be identified. In the specific application of the procedure, the focus is to be on driverless minibuses in local public transport in rural areas as a possible area of application for the technology. Although the research carried out on available solutions to the methodological challenge does not provide a directly applicable procedure from the fields of transport planning, technology assessment and technology evaluation, it does however provide helpful theoretical findings. These lead to a highly structured procedure that is suitable for the evaluation of a technology in mobility. The work phases are divided into a scoping process, a definition of the individual target system, a review of the application conditions, a synthesis of potential application scenarios and an analysis and comprehensive evaluation of the socio-technical system. The decisive valuation phase comprises the determination of individual target achievement, an understanding of the current impact structure and a multiperspective categorisation of the risks. When applying the previously developed procedure, various methods are used to access the “Test centre for automated buses in the district of Herzogtum Lauenburg”, which enables the practical testing of automated test vehicles and the participation of stakeholders, users and the public. As a result, the evaluation shows that the use of driverless vehicles in public transport cannot fundamentally solve the challenges of mobility in diverse rural areas. The anticipated great potential of driverless minibuses in terms of increased safety, cost reduction with dispersed demand and unrestricted social participation currently appears to be overestimated for the application under consideration. The application of the risk analysis reveals negative consequences of driverless driving: potential dangers with a high level of damage include, in particular, misuse or manipulation of the technology, negative environmental and health effects, lack of participation and high complexity with susceptibility to faults and corresponding consequences in the event of high technical dependency. Further specific risks are identified that influence social acceptance and people's current perceptions. The newly developed injustice factor can be used to differentiate between objectively unjust risks and subjectively critically perceived risks. However, it also becomes clear that a sudden, major irreversible extent of damage caused by driverless driving in road traffic has not yet been recognised. The overall conclusion is that driverless driving is not fundamentally the solution in terms of the defined objectives. The mobility system's overarching capabilities with optimised integration and interconnectivity of different means of transport must be considered, taking into account the individual needs in the respective area. Reliability, spatial and temporal flexibility with short access routes as well as manageability and comprehensibility play an important role here. Driverless driving, as a possible component of the overall mobility to be designed, requires further critical consideration and control so that it can have a holistically positive impact. The added value of this process results from the resolution of the complexity of a technology in the management and control dilemma under the production of structured orientation knowledge. A comprehensive socio-technical understanding of the system under consideration is achieved, which enables a realistic and holistic view of the capabilities and risks of the technology in a situational analysis. The chosen approach motivates the linking of different methods that place people and their individual needs at the centre of the sustainable development of technology.Bundesministerium für Verkehr (BMV
Deep generative models for unsupervised anomaly detection in magnetic resonance imaging of the brain
No full textThis thesis explores unsupervised anomaly detection in magnetic resonance imaging of the brain, leveraging generative models to model the distribution of healthy anatomy and identify deviations as anomalies. We examine the integration of additional contextual information into generative models and anomaly scoring methods. Our approaches enhance reconstruction quality and anomaly detection accuracy.Diese Arbeit untersucht die unüberwachte Anomalieerkennung in Magnet-Resonanz-Tomographie-Scans des Gehirns und nutzt generative Modelle, um die Verteilung gesunder Anatomie zu modellieren und Abweichungen als Anomalien zu identifizieren. Wir erforschen die Integration zusätzlicher kontextueller Informationen in generative Modelle und Anomaliebewertungsmethoden. Unsere Ansätze verbessern sowohl die Rekonstruktionsqualität als auch die Genauigkeit der Anomalieerkennung
Wet particle collisions simulated using the local front reconstruction method, a DNS approach
No full textIn addition to particles and gas, liquid is sometimes introduced into fluidized beds to, for example, cool the reactor or to provide reactants. However, the introduction of liquids can lead to agglomeration, which may be desirable or undesirable. To control the formation and impact of these agglomerates on the process, it is important to understand the collision of wet particles. To effectively understand the collision dynamics of wet particles, this work investigates the interaction between a wet particle and a dry particle using a novel Front-Tracking (FT) approach in combination with an Immersed Boundary Method (IBM). After thorough verification, extensive simulations were conducted producing excellent agreement with the experimental results of Bunke et al. (Chemical Engineering Journal, 2024, vol. 489, 151016). From the simulation results, the primary source of energy dissipation was found to be the extension of the liquid bridge directly after the collision, where the liquid is transferred to the liquid bridge effectively causing the deceleration of the particle. The friction coefficient, which is affected by the lubrication by the liquid, is a material property that should be modeled using the experimental value. Based on the simulation results, effective collision parameters for the hard-sphere model are obtained
An improved meshfree approach for solving nonlinear multivariate models involving aggregation, breakage, growth and source
No full textThe modeling of aggregation and collisional breakage phenomena remains largely unexplored due to nonlinearity and nonlocal nature of the model equation. This article discusses the performance and efficiency of a redefined homotopy-based method and generalized iteration method for solving bivariate aggregation-collision breakage model for several kinetic kernels. Solution for Brownian motion kernel and equi-partition of kinetic energy kernel are obtained to analyze the dynamics of bubble columns as well as the granular flow behavior. The iterative scheme is further extended to solve aggregation-breakage model with simultaneous growth and source terms. This model is also extended for solving bivariate cases
Continuous drying of alginate aerogel particles: Residence time measurement and process optimization under high pressure conditions
No full textThis study advances continuous supercritical carbon dioxide (scCO₂) drying of aerogel particles by introducing a non-invasive optical method to determine particle residence time in a countercurrent extraction column. In countercurrent operation, scCO₂ flows upward while the particle suspension in ethanol enters from the top. The method enables precise, real-time residence time measurement under high pressure conditions without disturbing the process. The effects of pressure (100–150 bar), temperature (40–80 °C), CO₂ flow rate (30–80 g/min), and suspension flow rate (10–45 g/min) on residence time and drying efficiency were accordingly analyzed. Experiments were performed in a 1.25 m high extraction column, with an internal diameter of 20.5 mm, using highly spherical alginate beads with a diameter of ∼ 400 µm as a model system. Evidence of effective solvent removal throughout the whole operation range was provided by determination of the residual ethanol content in the intact aerogel beads after the drying process (0.0053–0.0341 gethanol/gaerogel). The dried products featured a specific surface area of 363 ± 27 m²/g, a mesopore volume of 3.2 ± 0.7 cm³ /g, consistent with the typical range of alginate aerogels. The combined insights provide a comprehensive picture of the countercurrent column’s operational response and allow the definition of practical operating windows. Elevated temperature and high pressure provide the most favorable trade-off between short residence time and minimized residual ethanol, maximizing the time-specific yield. Overall, the approach establishes a robust, transferable framework for optimizing continuous scCO₂ drying of aerogel particles and supports extension to other particle sizes and formulations
Implementation of multi-level coarse-graining method on GPU using MUSEN
No full textGPU-based discrete element method (DEM) simulations have recently gained popularity due to their ability to reduce the computational costs associated with modelling large-scale granular systems. To further enhance the efficiency of these simulations, we implement the multi-level coarse-graining (MCG) method on GPU using the open-source GPU-accelerated DEM software MUSEN. The MCG method significantly improves performance by reducing the number of simulated particles while maintaining accuracy. The key simulation parameters such as the Verlet distance and the interval of performing refinement or coarsening of particles are optimized to maximize computational efficiency. The MCG-GPU method is validated using a hopper discharge system, achieving a speedup of about 3.4× compared to the MCG-CPU simulation. The robustness of this method is further demonstrated through its application to two industrial systems: a tablet-press feeder and a twin-screw feeder, where speedups of approximately 5.5× and 8×, respectively, are achieved relative to MCG-CPU simulations. These results affirm that the MCG-GPU method is a powerful tool for efficiently conducting large-scale particle simulations with complex geometries
Opportunities, environment and entrepreneur interaction: exploring the entrepreneurial process - insights from Germany and Japan -
No full textThis dissertation explores how entrepreneurial opportunities evolve into businesses through entrepreneur and environment interaction. It challenges the traditional view of opportunities, proposing that both discovery and creation are essential. With a multiple case-study design providing insights from German and Japanese start-ups, the research identifies four archetypical entrepreneurial processes based on the intensity and intention of interaction. The study contributes to entrepreneurship research by viewing the entrepreneurial process as an ongoing, iterative, and reciprocal relationship, with practical implications for policymakers and practitioners, especially in the context of demographic change.Diese Dissertation untersucht, wie sich aus Chancen durch die Interaktion zwischen Entrepreneur und Umwelt Unternehmen entwickeln. Sie stellt die traditionelle Sichtweise von Chancen in Frage und geht davon aus, dass sowohl Entdeckung und Schaffung von Bedeutung sind. Anhand multipler Fallstudien von deutschen und japanischen Start-up werden vier archetypische unternehmerische Prozesse identifiziert, die auf der Intensität und Absicht der Interaktion basieren. Die Studie leistet einen Beitrag zur Entrepreneurship-Forschung, durch die Betrachtung des unternehmerischen Prozesses als fortlaufende, iterative und wechselseitige Beziehung, insbesondere im Kontext demografischen Wandels
Reactors for fluid-solid reactions: Fixed bed reactors
No full textFixed bed reactors are the most commonly used reactor type in the chemical and petrochemical industry. They are also used for mobile and stationary exhaust gas cleaning. All fixed bed reactors have in common that a solid, usually a catalyst, is spatially fixed in the reactor and is flowed through or over by the reaction mixture. This chapter provides an overview of this important reactor type, with the focus on catalytic fixed bed reactors for gas reactions. After a brief introduction, catalytic fixed bed reactors are classified according to the type of involved phases, the structure of the catalyst phase, and the temperature control. The operating principle of the different reactor types is explained using examples. In addition to fixed bed reactors in industry, fixed bed reactors in laboratory and research are also discussed, which are used for high-throughput screening, for measuring kinetic data, or for operando spectroscopy on catalysts. Subsequently, the mathematical modeling of fixed bed reactors is discussed. The classification of the different modeling approaches includes the dimension of the modeling domain, the mathematical structure of the equations, the description of transport processes, the number and type of involved phases, and the description of the reaction kinetics. In addition to the classic pseudo-homogeneous, pseudo-heterogeneous and heterogeneous reactor models modern modeling approaches such as the CFD simulation of catalytic fixed bed reactors are presented using examples. Finally, the unsteady operation and the dynamic behavior of fixed bed reactors are addressed. In this context, the parametric sensitivity, the thermal runaway, and the periodic flow reversal are examined in more detail
Predicting soil stress–strain behaviour with bidirectional long short-term memory networks
No full textPurpose
Artificial intelligence, particularly deep learning (DL), has increasingly influenced various scientific fields, including soil mechanics. This paper aims to present a novel DL application of long short-term memory (LSTM) networks for predicting soil behaviour during constant rate of strain (CRS) tests.
Design/methodology/approach
LSTMs are adept at capturing long-term dependencies in sequential data, making them suitable for predicting the complex, nonlinear stress–strain behaviour of soil. This paper evaluates various LSTM configurations, optimising parameters such as step size, batch size, data sampling rate and training subset size to balance prediction accuracy and computational efficiency. The study uses a comprehensive data set from numerical finite element method simulations conducted with PLAXIS 2D and laboratory CRS tests.
Findings
The proposed LSTM model, trained on data at lower stress levels, accurately forecasts soil behaviour at higher stress levels. The optimal LSTM setup achieved a median error of 3.59% and 5.10% for numerical data and 3.86% for laboratory data, presenting the setup’s effectiveness.
Originality/value
This approach reduces the required time to complete extensive laboratory testing, aligning with sustainable industrial practices. The findings suggest that LSTM networks can enhance geotechnical engineering applications by efficiently predicting soil behaviour