178 Works

Product-property guided scale-up of a fluidized bed spray granulation process using the CFD-DEM method

Paul Kieckhefen, Swantje Pietsch-Braune & Stefan Heinrich
In this work, a method to predict the surface structures of particles produced by fluidized bed spray layering granulation using the CFD-DEM method was developed. A simple state-variable/event tracking approach was implemented to capture indirect quantifiers of the progression of structure-forming microprocesses. The state of the droplet at the time of impact on the particle surface, as well as the time required for drying, is correlated to product properties that quantify surface structure morphology such...

Controlling the solid-state reaction in Fe-MoS2 self-lubricating composites for optimized tribological properties

Gabriel Araujo de Lima, Aloisio Nelmo Klein & Kaline Pagnan Furlan
In this work, self-lubricating composites containing MoS2 and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS2 reacts with iron matrixes during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS2 with iron...

Lagrangian sensors in a stirred tank reactor: comparing trajectories from 4D-Particle Tracking Velocimetry and Lattice-Boltzmann simulations

Sebastian Hofmann, Christian Weiland, Jürgen Fitschen, Alexandra von Kameke, Marko Hoffmann & Michael Schlüter
In this study, three-dimensional flow measurements by means of 4D-Particle Tracking Velocimetry (4D-PTV) are carried out in a laboratory-scale 3 L stirred tank reactor in order to investigate the flow-following behavior of two different inertial particle types, Polyethylene (PE) particles and alginate beads, at different impeller frequencies. Applied particles mimic Lagrangian sensor particles, which are intended to determine process parameters such as oxygen concentration at their corresponding position inside a bioreactor. Accompanying Lattice-Boltzmann Large Eddy...

Automatisierte Probenfiltration zur Analyse intrazellulärer Metaboliten bei höheren Biomassekonzentrationen

Enrico Hans & An-Ping Zeng
Die meisten Stoffwechseluntersuchungen hinsichtlich intrazellulärer Metaboliten für Corynebacterium glutamicum-Stämme wurden bisher mit Biomassekonzentrationen £ 10 g L–1 durchgeführt. Innerhalb der vorliegenden Arbeit konnte gezeigt werden, dass Untersuchungen bis Konzentrationen von 32 g L–1 möglich sind. Die Modifikation einer automatisierten Schnellfiltration weist den Weg zu weiteren zeitlichen Verkürzungen auf. Außerdem konnte mithilfe der Filtration der Einfluss einer genetischen Modifikation der Aspartokinase zur Unterdrückung der Inhibierung im Aspartatstoffwechsel quantifiziert werden.

Anomalous collapse of interacting bubbles in a fluidized bed : a magnetic resonance imaging study

Christopher M. Boyce, Alexander Penn, Azin Padash, M. Lehnert, Klaas P. Prüssmann & Christoph Müller
The collapse, or reduction in size to zero volume, of bubbles injected into incipiently fluidized beds was studied using rapid magnetic resonance imaging. The collapse of a smaller lower bubble trailing a larger upper bubble and the collapse of one bubble when two bubbles rose side by side were found to occur. Under the same conditions with the use of finer particles or the injection of an isolated bubble, no collapse occurred. Thus, results indicate...

Influence of pitting corrosion on the fatigue strength of offshore steel structures based on 3D surface scans

Sulaiman Shojai, Peter Schaumann, Moritz Braun & Sören Ehlers
Support structures for offshore wind turbines and the corresponding transformer platforms are highly susceptible to corrosion. In particular, the phenomenon of pitting is crucial, as it leads to local stress concentrations and thus affects the fatigue life of structures. Despite corrosion protection systems, corrosion cannot be completely avoided, which can lead to pitting corrosion on the steel surface. This leads to fatigue life reduction, since the structures are exposed to high dynamic loads. Local stress...

Standardization of risk assessment in navigation

Jens Froese
Marine traffic safety assessed by quantitative instead of qualitative methods is increasingly required. There are mature methods available to conduct a quantitative risk assessment such as IWRAP [1], resulting in collision and grounding probabilities. There is, however, the difficulty to determine the so-called causation factor having an impact on the results but there is currently no reliable method to fix it. To globally collect relevant empirical data to allow a statical determination could make risk...

Experimental and numerical investigation of the deformation behaviour of cables and thin beam-like structures under multi-axial loading

André Hildebrandt-Raj, Prateek Sharma, Alexander Düster & Stefan Diebels
In various applications, it is common to use thin beam-like structures, made of plastic or fibre-reinforced materials, as well as components such as cables. They are flexible, and the most common form of deformation is bending, but they can also be stretched or torqued. Due to their structural composition, a coupling between the different loading directions exists. This is especially pronounced for cables, where the different components interact with each other and the kinematics of...

A novel approach for visualizing mixing phenomena of reactive liquid-liquid flows in milli- and micro-channels

Torben Frey, Felix Kexel, Kayla Reata Dittmer, Sven Bohne, Marko Hoffmann, Hoc Khiem Trieu & Michael Schlüter
Modular milli- and micro-structured systems represent a promising approach to exploit the potential of micro-process technology, including precise reaction control and scale-up. A major drawback of micro-structured devices is fouling and mixing mechanisms need to be investigated phenomenologically to better understand the processes that lead to fouling. Previous work was conducted to resolve 3D concentration fields by means of Laser-Induced Fluorescence (LIF) using a Confocal Laser Scanning Microscope (CLSM) (Frey et al., J Flow Chem,...

Chromium removal in the presence of NOM during Fe(II) reductive precipitation for drinking water treatment

Margarethe Langer, Mohammad Umair Jamal, Amanda Conklin & Mathias Ernst
Cr(VI) is toxic and carcinogenic, which fuels discussions on reducing existing standards for maximum Cr concentrations in drinking water. Fe(II) reductive precipitation is a common and economical method for achieving very low Cr(tot) concentrations (<5 µg/L). While Cr(VI) is reduced to Cr(III), Fe(II) is oxidized to Fe(III). The resulting Cr(III) and Fe(III) have low solubilities at neutral pH, precipitate as hydroxides, and can be removed by conventional media filtration. The presence of natural organic matter...

Combinatorial n-fold integer programming and applications

Dušan Knop, Martin Koutecký & Matthias Mnich
Many fundamental NP-hard problems can be formulated as integer linear programs (ILPs). A famous algorithm by Lenstra solves ILPs in time that is exponential only in the dimension of the program, and polynomial in the size of the ILP. That algorithm became a ubiquitous tool in the design of fixed-parameter algorithms for NP-hard problems, where one wishes to isolate the hardness of a problem by some parameter. However, in many cases using Lenstra’s algorithm has...

Helical milling of bore holes in Ti6Al4V parts produced by selective laser melting with simultaneous support structure removal

Wolfgang Hintze, Robert Schötz, Jan Philipp Mehnen, Lars Köttner & Carsten Möller
Selective Laser Melting (SLM) is a powder bed based Additive Manufacturing (AM) process that is currently being established in the series production of Ti6Al4V components in the aviation industry. One advantage is the significantly lower Buy-to-Fly ratio. However, subsequent machining is necessary in order to remove support structures of the SLM process and to fulfill quality requirements. Experimental results on support structure removal and simultaneous finishing of holes by helical milling are presented. Engagement conditions...

Process types of customisation and personalisation in design for additive manufacturing applied to vascular models

Johanna Spallek & Dieter Krause
Manufacturing companies face high demand for products that fulfil individual customer desires. Recent improvements in additive manufacturing (AM) enable the fabrication of customer-specific components of a product. This paper presents a categorisation of design processes for customised and personalised products through the use of AM in three process types: special design, specific adaptation, and standardised individualisation. The characteristics of design processes are examined in medical development of vascular models integrated into a modular neurovascular training...

Analysis of design guidelines for automated order acceptance in additive manufacturing

Jan-Peer Rudolph & Claus Emmelmann
Additive manufacturing (AM) is increasingly used in industrial production. Compared to conventional manufacturing technologies, such as milling and casting, AM offers a high degree of design freedom. Nevertheless, still some manufacturing restrictions and design guidelines have to be considered to ensure a flawless production. Therefore, a checking of design guidelines is a necessary step in order acceptance. Addressing this need, this paper presents an integrated analysis of design guidelines for an automated order acceptance. In...

Analysis and Modeling of Heat Flux into the Tool in Abrasive Circular Cutting of Unidirectional CFRP

Wolfgang Hintze & Christian Klingelhöller
For edge trimming of slightly curved thin walled CFRP parts dry circular cutting is a promising alternative. However, a high fraction of the cutting energy is converted into heat. The study focuses on the determination of the amount of heat dissipated by the tool in circular cutting of unidirectional CFRP with epoxy matrix. An inverse heat conduction model is developed and solved for a set of temperature profiles measured on the tool surface with an...

Influence of curved workpiece contours on delamination during end milling of FRP

Wolfgang Hintze & Felix Brügmann
When end milling long fiber reinforced composites, fiber protrusions of the top layers can occur. The lengths of fiber protrusions found on real workpieces with curved contours cannot be explained so far. The lengths of individual fibers to be cut along the tool path depend on tool diameter, local fiber orientation and path geometry. All fibers are separated into two ends at the initial contact with the tool. They define the theoretical maximum lengths of...

Extension of the strain energy density method for fatigue assessment of welded joints to sub-zero temperatures

Moritz Braun, Claas Fischer, Wolfgang Fricke & Sören Ehlers
Within stress-based fatigue assessment concepts, causes that do not influence the fatigue stress parameters, such as temperature, can only be accounted for by means of modification factors. The strain energy density (SED) method allows to account for changing material support effects and Young's modulus with temperature directly. Thus, in this study, a concept is presented to extend the SED method for fatigue assessment of welded joints at sub-zero temperatures. For this purpose, fatigue test results...

Bildgebende UV/VIS‐Spektroskopie zur Untersuchung des Einflusses der Fluiddynamik auf die Entstehung von Haupt‐ und Nebenprodukt in schnellen konkurrierenden konsekutiven Gas‐Flüssig‐Reaktionen

Felix Kexel, Alexandra von Kameke, Martin Oßberger, Marko Hoffmann, Peter Klüfers & Michael Schlüter
Zur Bildung vieler Bulk‐Chemikalien müssen gasförmige Stoffe mit einer kontinuierlichen flüssigen Phase vermischt und zur Reaktion gebracht werden. Häufig kommt es dabei zur Entstehung unerwünschter Nebenprodukte. Wie die Entstehung eines Nebenprodukts einer schnellen konkurrierenden Folgereaktion durch die Zeitskalen der Vermischung beeinflusst werden kann wird untersucht. Zum Einsatz kommt ein Taylor‐Blasen‐Experiment, bei dem die Zeitskalen der Vermischung systematisch und reproduzierbar variiert werden können. Es zeigt sich, dass der Vermischung in der Wirbelschleppe einer Blase hinsichtlich der...

Spatially localized vibrations in a rotor subjected to flutter

Alessandro Nitti, Merten Stender, Norbert Hoffmann & Antonio Papangelo
The current push toward lightweight structures in aerospace and aeronautical engineering is leading to slender design airfoils, which are more likely to undergo large deformation, hence experiencing geometrical nonlinearities. The problem of vibration localization in a rotor constituted by N coupled airfoils with plunge and pitch degrees of freedom subjected to flutter instability is considered. For a single airfoil, it is shown that depending on the system parameters, multiple static and dynamic equilibria coexist which...

Needle tip force estimation by deep learning from raw spectral OCT data

Martin Gromniak, Nils Thorben Gessert, Thore Saathoff & Alexander Schlaefer
Purpose: Needle placement is a challenging problem for applications such as biopsy or brachytherapy. Tip force sensing can provide valuable feedback for needle navigation inside the tissue. For this purpose, fiber-optical sensors can be directly integrated into the needle tip. Optical coherence tomography (OCT) can be used to image tissue. Here, we study how to calibrate OCT to sense forces, e.g., during robotic needle placement. Methods: We investigate whether using raw spectral OCT data without...

The development of risk aversion and prudence in Chinese children and adolescents

Timo Heinrich & Jason M. Shachat
This study experimentally evaluates the risk preferences of children and adolescents living in an urban Chinese environment. We use a simple binary choice task that tests risk aversion, as well as prudence. This is the first test for prudence in children and adolescents. Our results reveal that subjects from grades 5 to 11 (10 to 17 years) make mostly risk-averse and prudent choices. The choices of 3rd graders (8 to 9 years) do not differ...

A machine learning-based method for simulation of ship speed profile in a complex ice field

Aleksandar-Saša Milaković, Fang Li, Mohamed Marouf & Sören Ehlers
Computational methods for predicting ship speed profile in a complex ice field have traditionally relied on mechanistic simulations. However, such methods have difficulties capturing the entire complexity of ship–ice interaction process due to the incomplete understanding of the underlying physical phenomena. Therefore, data-driven approaches have recently gained increased attention in this context. Hence, this paper proposes a concept of a first machine learning-based simulator of ship speed profile in a complex ice field. The developed...

Microstructure and mechanical behavior of TiO₂-MnO-doped alumina/alumina laminates

Marcelo Daniel Barros, Hans Jelitto, Dachamir Hotza & Rolf Janßen
Tapes of TiO2-MnO-doped alumina (d-Al2O3) and pure alumina (Al2O3) were shaped via tape casting. Laminates with three different layer numbers and respective thicknesses were produced and sintered at 1200°C. The microstructure and mechanical behavior of laminates were investigated and compared to the respective monolithic references (d-Al2O3 and Al2O3). The use of dopants in alumina decreased the initial sintering temperature, leading to higher densification at 1200°C (~98% theoretical density (TD)) when compared to Al2O3 (~73% TD)....

The inhomogeneous Cauchy-Riemann equation for weighted smooth vector-valued functions on strips with holes

Karsten Kruse
This paper is dedicated to the question of surjectivity of the Cauchy-Riemann operator ∂¯ on spaces EV(Ω, E) of C∞-smooth vector-valued functions whose growth on strips along the real axis with holes K is induced by a family of continuous weights V. Vector-valued means that these functions have values in a locally convex Hausdorff space E over C. We derive a counterpart of the Grothendieck-Köthe-Silva duality O(C\ K) / O(C) ≅ A(K) with non-empty compact...

Model-assisted DoE software: optimization of growth and biocatalysis in Saccharomyces cerevisiae bioprocesses

André Moser, Kim Beatrice Kuchemüller, Sahar Deppe, Tanja Hernández Rodríguez, Björn Frahm, Ralf Pörtner, Volker C. Hass & Johannes Möller
Bioprocess development and optimization are still cost- and time-intensive due to the enormous number of experiments involved. In this study, the recently introduced model-assisted Design of Experiments (mDoE) concept (Möller et al. in Bioproc Biosyst Eng 42(5):867, https://doi.org/10.1007/s00449-019-02089-7, 2019) was extended and implemented into a software (“mDoE-toolbox”) to significantly reduce the number of required cultivations. The application of the toolbox is exemplary shown in two case studies with Saccharomyces cerevisiae. In the first case study,...

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