119 Works

Fragmentation of beaded fibres in a composite

Carol Winnifred Rodricks, Israel Greenfeld, Bodo Fiedler & Hanoch Daniel Wagner
The fibre–matrix interface plays an important role in the overall mechanical behaviour of a fibre-reinforced composite, but the classical approach to improving the interface through chemical sizing is bounded by the materials’ properties. By contrast, structural and/or geometrical modification of the interface may provide mechanical interlocking and have wider possibilities and benefits. Here we investigate the introduction of polymer beads along the interface of a fibre and validate their contribution by a single fibre fragmentation...

Statistical analysis of sub-zero temperature effects on fatigue strength of welded joints

Moritz Braun
Ships and offshore structures in Arctic environments are exposed to severe environmental actions and sub-zero temperatures. Thus, the design of such structures has to account for the Arctic environment and must be cost-efficient at the same time. A vital part of the design process is to ensure that fatigue-induced failure does not occur in the lifetime of the structure. While effects of high temperatures on material behavior are well covered in international standards and guidelines,...

Utility-based operation management for low voltage distribution grids using online optimization

Hanko Ipach, Leonard Fisser, Christian Becker & Andreas Timm-Giel
Wir stellen einen Betriebsführungsregler für Niederspannungsnetze vor, der eine Vielzahl dezentraler Energieanlagen (DEA) in Echtzeit koordiniert, um die Nutzung der erneuerbaren Energieerzeugung zu maximieren. Der Regler verwendet ein LTE-Funknetzwerk, das die DEA mit dem Verteilnetzbetreiber verbindet. In unserem Ansatz werden den DEA Nutzenfunktionen zugewiesen und die Nutzenmaximierung wird als Optimierungsproblem formuliert. Das Optimierungsproblem wird durch einen iterativen Algorithmus gelöst, der inkrementelle Anpassungen der Leistungssollwerte der DEA in Richtung des Optimums vornimmt. Um den Netzzustand im...

Enabling cost-based support structure optimization in laser powder bed fusion of metals

Katharina Bartsch & Claus Emmelmann
Support structures are essential to laser powder bed fusion (PBF-LB/M). They sustain overhangs, prevent distortion, and dissipate process-induced heat. Their removal after manufacturing is required, though, increasing the overall costs. Therefore, optimization is important to increase the economic efficiency of PBF-LB/M. To enable optimization focused on the support structures’ costs, a cost model is developed. The whole production process, including the design, manufacturing, and post-processing of a part, is considered by deriving formulas for the...

Slice thickness optimization for the focused ion beam-scanning electron microscopy 3D tomography of hierarchical nanoporous gold

Alexander Shkurmanov, Tobias Krekeler & Martin Ritter
The combination of focused ion beam (FIB) with scanning electron microscopy (SEM), also known as FIB-SEM tomog raphy, has become a powerful 3D imaging technique at the nanometer scale. This method uses an ion beam to mill away a thin slice of material, which is then block-face imaged using an electron beam. With consecutive slicing along the z-axis and subsequent imaging, a volume of interest can be reconstructed from the images and further analyzed. Hierarchical...

Community detection for access-control decisions: analysing the role of homophily and information diffusion in online social networks

Nicolás Díaz Ferreyra, Tobias Hecking, Esma Äimeur, Maritta Heisel & Heinz Ulrich Hoppe
Access-Control Lists (ACLs) (a.k.a. friend lists) are one of the most important privacy features of Online Social Networks (OSNs) as they allow users to restrict the audience of their publications. Nevertheless, creating and maintaining custom ACLs can introduce a high cognitive burden on average OSNs users since it normally requires assessing the trustworthiness of a large number of contacts. In principle, community detection algorithms can be leveraged to support the generation of ACLs by mapping...

Anomaly detection for industrial surface inspection : application in maintenance of aircraft components

Falko Kähler, Ole Schmedemann & Thorsten Schüppstuhl
Surface defects on aircraft landing gear components represent a deviation from a normal state. Visual inspection is a safety-critical, but recurring task with automation aspiration through machine vision. Various rare occurring faults make acquisition of appropriate training data cumbersome, which represents a major challenge for artificial intelligence-based optical inspection. In this paper, we apply an anomaly detection approach based on a convolutional autoencoder for defect detection during inspection to encounter the challenge of lacking and...

Strain evolution and novel downstream processing with integrated catalysis enable highly efficient coproduction of 1,3-propanediol and organic acid esters from crude glycerol

Chijian Zhang, Shubhang Sharma, Cheng-Wei Ma & An-Ping Zeng
Bioconversion of natural microorganisms generally results in a mixture of various compounds. Downstream processing (DSP) which only targets a single product often lacks economic competitiveness due to incomplete use of raw material and high cost of waste treatment for by-products. Here, we show with the efficient microbial conversion of crude glycerol by an artificially evolved strain and how a catalytic conversion strategy can improve the total products yield and process economy of the DSP. Specifically,...

Robotic die-less forming strategy for fiber-reinforced plastic composites production

Jan-Erik Rath, Lea-Sophie Schwieger & Thorsten Schüppstuhl
Fiber-reinforced plastics (FRP) production in many cases involves expensive molds, which especially hinders cost-effective production of small series and prototypes. In metal parts production, incremental sheet forming (ISF) is an established process for creating individual parts and small series through a flexible and die-less process. Establishing a similar process for FRP is desirable but challenging, as deformation mechanisms of endless FRP differ significantly from metal sheets. Using just two movable standard tools, bending and shear...

Localized delivery of liquid fertilizer in coarse-textured soils using foam as carrier

Mohammad Javad Shojaei, Dani Or & Nima Shokri
Agrochemicals and fertilizers are central to modern agriculture and are credited with the large increase of crop yield as a part of the Green Revolution of the 1960’s. Timely and targeted fertilizer application to crop root zones enhances effectiveness and reduces unintended release to the environment. This is particularly important for highly mobile liquid fertilizers (e.g., nitrate) that can be mobilized with infiltrating water to bypass root-bearing soil volumes. We report a novel liquid fertilizer...

Scale-resolving turbulent channel flow simulations using a dynamic cumulant lattice Boltzmann method

Martin Gehrke & Thomas Rung
This paper reports the assessment of a modified cumulant lattice Boltzmann method in turbulent channel flows. The suggested approach is of interest for its resolution-spanning capabilities, which are scrutinized for grid resolutions between 4 and 430 wall units. With the emphasis on a recently published parameterized cumulant collision operator, we suggest a resolution-sensitive regularization supplemented by a dynamic subgrid-scale model based upon third-order cumulant expressions, which seamlessly vanishes for direct numerical simulations. The strategy is...

Decolorization and control of bromate formation in membrane ozonation of humic-rich groundwater

Jakob Kämmler, Garyfalia Zoumpouli, Jörn Sellmann, Y. M. John Chew, Jannis Wenk & Mathias Ernst
Membrane ozonation of bromide-containing, high-color natural organic matter (NOM) containing groundwater was performed using single-tube polydimethylsiloxane (PDMS) and multi-tube polytetrafluoroethylene (PTFE) membrane contactors, and compared to batch ozonation. For membrane ozonation, dissolved ozone concentration, water color (VIS436), ultraviolet light absorption (UV254) and bromate formation were correlated with ozone dose, ozone gas concentration, hydraulic retention time and Hatta number (Ha). NOM color removal of up to 45 % for the single-tube contactor and 17 % for...

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...

A modified level set method for topology optimization of sparsely-filled and slender structures

Ali Azari Nejat, Alexander Held, Niklas Trekel & Robert Seifried

Bridging the gap between coastal engineering and nature conservation?: A review of coastal ecosystems as nature-based solutions for coastal protection

Philipp Jordan & Peter Fröhle
Under the umbrella term of Nature-based Solutions (NbS) fall measures from a wide range of disciplines. With regard to coastal protection, coastal ecosystems represent possible and promising NbS to coastal threats such as storm surges or erosion. Around the globe, the looming climate change and related developments in the coastal landscapes as well as a paradigm shift in societal views shifted the focus of decision-makers and researchers onto NbS for coastal protection, driving the need...

Energy dissipation in horizontally driven particle dampers of low acceleration intensities

Niklas Meyer & Robert Seifried
The energy dissipation in sinusoidally driven particle dampers is highly dependent on the motion mode of the particle bed. Especially, for applications of low acceleration intensity, i.e., acceleration amplitude below gravitational acceleration, only small energy dissipation rates are obtained so far, due to sticking of particles. Here, a new and more efficient design of particle dampers is introduced for such applications, whereby the focus is on horizontal vibrations. The proposed design makes use of the...

Registration Year

  • 2022

Resource Types

  • Journal Article