110 Works

Efficient hybrid 3D system calibration for magnetic particle imaging systems using a dedicated device

Anselm von Gladiß, Matthias Gräser, André Behrends, Xin Chen & Thorsten M. Buzug
Image reconstruction in magnetic particle imaging is often performed using a system matrix based approach. The acquisition of a system matrix is a time-consuming calibration which may take several weeks and thus, is not feasible for a clinical device. Due to hardware characteristics of the receive chain, a system matrix may not even be used in similar devices but has to be acquired for each imager. In this work, a dedicated device is used 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...

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...

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...

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...

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...

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,...

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.

Flexible multibody impact simulations based on the isogeometric analysis approach

Tobias Rückwald, Alexander Held & Robert Seifried
Usually detailed impact simulations are based on isoparametric finite element models. For the inclusion in multibody dynamics simulation, e.g. in the framework of the floating frame of reference, a previous model reduction is necessary. A precise representation of the geometry is essential for modeling the dynamics of the impact. However, isoparametric finite elements involve the discretization of the geometry. This work tests isogeometric analysis (IGA) models as an alternative approach in the context of impact...

Fatigue strength of PBF-LB/M and wrought 316L stainless steel : effect of post-treatment and cyclic mean stress

Moritz Braun, Eduard Mayer, Igor Kryukov, Christian Wolf, Stefan Böhm, Aliakbar Taghipour, Rachael Elizabeth Wu, Sören Ehlers & Shahram Sheikhi
Additive manufacturing (AM) enables the cost-effective production of complex components, many of which are traditionally manufactured using costly subtractive processes. During laser-based powder bed fusion of metals (PBF-LB/M), internal pores and rough surfaces are typically inevitable, reducing fatigue and corrosion resistance compared to traditional processes. Additionally, large defects often occur near to or at surfaces. Thus, this study investigates the effect of hybrid additive and subtractive manufacturing on the fatigue strength of AISI 316L. To...

Nanoporous-gold-polypyrrole hybrid materials for millimeter-sized free standing actuators

Benedikt Roschning & Jörg Weissmüller
Advanced Materials Interfaces published by Wiley-VCH GmbH This work studies the actuation of hybrid materials made from nanoporous gold, polypyrrole, and aqueous electrolyte. The deposition protocol affords a conformal polypyrrole coating on the entire internal interface of millimeter-sized nanoporous metal specimens made by dealloying. The hybrid material emerges when the remaining pore space is filled with perchloric acid. The metal serves as load-bearing and electronically conductive substrate, the polypyrrole as functional active component for actuation,...

Experimental investigation on the influence of welding residual stresses on fatigue for two different weld geometries

Nils Friedrich
Fatigue & Fracture of Engineering Materials & Structures published by John Wiley & Sons Ltd Fatigue tests on welded small-scale specimens often do not show a distinct residual stress influence. An exception is longitudinal stiffeners, which are therefore frequently used to study the influence of welding residual stresses on fatigue. The results are not directly transferable to other weld geometries because the residual stress distribution depends on the weld geometries. In the presented investigation, fatigue...

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...

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,...

CFD analysis of asymmetric mixing at different inlet configurations of a split-and-recombine micro mixer

Torben Frey, Rieke Schlütemann, Sebastian Schwarz, Philip Biessey, Marko Hoffmann, Marcus Grünewald & Michael Schlüter
In the scope of the ENPRO II initiative (Energy Efficiency and Process Intensification for the Chemical Industry), a major challenge of process intensification of polymer synthesis in continuous systems is fouling. Pre-mixing is a key aspect to prevent fouling and is achieved through milli and micro structured devices (Bayer et al. 1). While equal volume flow ratios are well investigated in milli and micro systems, asymmetric mixing tasks have received less attention. This paper investigates...

Weighted spaces of vector-valued functions and the ε-product

Karsten Kruse
We introduce a new class FV(Ω , E) of weighted spaces of functions on a set Ω with values in a locally convex Hausdorff space E which covers many classical spaces of vector-valued functions like continuous, smooth, holomorphic or harmonic functions. Then we exploit the construction of FV(Ω , E) to derive sufficient conditions such that FV(Ω , E) can be linearised, i.e. that FV(Ω , E) is topologically isomorphic to the ε-product FV(Ω) εE...

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...

Platform of design method for developing mobility-preserving products

Kristin Paetzold, Sandro Wartzack & Dieter Krause
© 2014 Published by Elsevier B.V. Preserving the mobility of elderly people is becoming increasingly important, as other factors of quality of life, such as autonomy or participation in social life, are connected with mobility. Starting from an analysis of elderly people as users, combined with the analysis of mobility and mobility situations, a catalog of functions is presented in this paper, which provides the basis for a methods platform to develop user adapted modular...

Continuing education and personalization of design methods to improve their acceptance in practice : an explorative study

Selin Üreten, Gregor Beckmann, Eilika Schwenke, Dieter Krause & Shi Cao
One possibility to establish and foster efficient method transfer from academia to industry is via the heads of professional designers and design students. The transfer and use of design methods in a sustainable way is related to the methods' acceptance by the user which is accompanied by many challenges. Educational concepts and design method adaptions have been chosen as decisive control parameters among many others in order to understand and evaluate how these can influence...

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...

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...

Potential Dynamics of CO2 Stream Composition and Mass Flow Rates in CCS Clusters

Sven-Lasse Kahlke, Martin Pumpa, Stefan Schütz, Alfons Kather & Heike Rütters
Temporal variations in CO2 stream composition and mass flow rates may occur in a CO2 transport network, as well as further downstream when CO2 streams of different compositions and temporally variable mass flow rates are fed in. To assess the potential impacts of such variations on CO2 transport, injection, and storage, their characteristics must be known. We investigated variation characteristics in a scenario of a regional CO2 emitter cluster of seven fossil-fired power plants and...

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...

Prä-operationelle Vorhersage von Seegang und Wellenauflauf an Seedeichen in der deutschen Bucht

Norman Dreier & Peter Fröhle
Die heutigen verfügbaren Frühwarnsysteme für Sturmfluten an der deutschen Nordseeküste basieren ausschließlich auf der Vorhersage lokaler Wasserstände. Andere hydrodynamische Belastungen, welche z. B. durch Windwellen und lokale Strömungen hervorgerufen werden, sowie die Widerstandsfähigkeit der Küstenschutzbauwerke (Seedeiche, Ufermauern etc.) werden in der Regel nicht berücksichtigt. Daher wurde ein Prototyp für ein operationelles Echtzeit- und Vorhersagesystem (im Nachfolgenden als „prä-operationelles“ Vorhersagesystem bezeichnet) für Seegang und seegangsinduzierte Belastungen auf der Basis von Naturmessungen und numerischen Simulationen bzw. empirischen...

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