29 Works

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...

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...

Conversion of whey protein aerogel particles into oleogels : effect of oil type on structural features

Stella Plazzotta, Isabella Jung, Baldur Schroeter, Raman Subrahmanyam, Irina Smirnova, Sonia Calligaris, Pavel Gurikov & Lara Manzocco
Protein aerogel particles prepared by supercritical-CO2-drying (SCD) of ground whey protein (WP) hydrogels (20% w/w, pH 5.7) were converted into oleogels by dispersion in selected edible oils (castor, cod liver, corn, flaxseed, MCT, peanut and sunflower oil). The obtained oleogels were analysed for oil content, microstructure, rheological properties, and ATR-FTIR spectra. Except for castor oil, solid-like, plastic materials with comparable composition (80% oil, 20% WP) and rheological properties (G′~3.5 × 105 Pa, G″~0.20 × 105...

Talking about the likelihood of risks : an agent-based simulation of discussion processes in risk workshops

Clemens Harten, Matthias Meyer & Lucia Bellora-Bienengräber
Purpose: This paper aims to explore drivers of the effectiveness of risk assessments in risk workshops. Design/methodology/approach: This study uses an agent-based model to simulate risk assessments in risk workshops. Combining the notions of transactive memory and the ideal speech situation, this study establishes a risk assessment benchmark and then investigates real-world deviations from this benchmark. Specifically, this study models limits to information transfer, incomplete discussions and potentially detrimental group characteristics, as well as interaction...

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...

A novel approach to achieving end-to-end QoS for avionic applications

Yevhenii Shudrenko, Daniel Plöger, Koojana Kuladinithi & Andreas Timm-Giel
Future Internet of Things (IoT) applications, such as connected industry 4.0, become more challenging with the strict Quality of Service (QoS) requirements, including reliability and delay guarantees. Several mechanisms in the communication stack to match the expected QoS are already discussed and specified at different layers, with the goal to make the communication more reliable. They focus on the layer-specific enhancements. For example, Time-Slotted Channel Hopping (TSCH) is a link layer mechanism to avoid narrowband...

Curvature sensing of a soft robot based on conductive foam

Malte Grube & Robert Seifried
Soft material robots are an emerging and fast-growing field of research [1] with potential application in various technical fields. These applications include, but are not limited to medical applications and all sorts of human-machine-interaction. Due to the soft structure, conventional components and design methodologies are not applicable. For reliable control and positioning of soft robots in 3D space especially accurate knowledge about their current position and orientation is essential. In this contribution, a resistive curvature...

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...

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...

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,...

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...

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...

Three dimensional flows beneath a thin layer of 2D turbulence induced by Faraday waves

Raffaele Colombi, Michael Schlüter & Alexandra von Kameke
Abstract: Faraday waves occur on a fluid being subject to vertical shaking. Although it is well known that form and shape of the wave pattern depend on driving amplitude and frequency, only recent studies discovered the existence of a horizontal velocity field at the surface, called Faraday flow. This flow exhibits attributes of two-dimensional turbulence and is replicated in this study. Despite the increasing attention towards the inverse energy flux in the Faraday flow and...

Extension of vector-valued functions and weak-strong principles for differentiable functions of finite order

Karsten Kruse
In this paper we study the problem of extending functions with values in a locally convex Hausdorff space E over a field K, which has weak extensions in a weighted Banach space Fν(Ω,K) of scalar-valued functions on a set Ω, to functions in a vector-valued counterpart Fν(Ω,E) of Fν(Ω,K). Our findings rely on a description of vector-valued functions as continuous linear operators and extend results of Frerick, Jordá and Wengenroth. As an application we derive...

A novel p-harmonic descent approach applied to fluid dynamic shape optimization

Peter Marvin Müller, Niklas Kühl, Martin Siebenborn, Klaus Deckelnick, Michael Hinze & Thomas Rung
We introduce a novel method for the implementation of shape optimization for non-parameterized shapes in fluid dynamics applications, where we propose to use the shape derivative to determine deformation fields with the help of the p- Laplacian for p> 2. This approach is closely related to the computation of steepest descent directions of the shape functional in the W1,∞- topology and refers to the recent publication Deckelnick et al. (A novel W1,∞ approach to shape...

Production of polylactic acid aerogels via phase separation and supercritical CO2 drying: thermodynamic analysis of the gelation and drying process

Alberto Bueno Morales, Christian Lübbert, Sabine Enders, Gabriele Sadowski & Irina Smirnova
The application range of aerogels, especially in the life-science sector, can be extended by utilizing biocompatible polymers such as polylactic acid (PLA). However, the low glass transition temperature (Tg) of PLA and the challenging gelation techniques limit the application of supercritical CO2 (scCO2) drying and thus the PLA-aerogel production. The aim of this work is to overcome this challenge and to provide a better understanding of the thermodynamics of the process. Therefore, the gelation of...

An empirical study on stress-based fail-safe topology optimization and multiple load path design

Micah Kranz, Julian Kajo Lüdeker & Benedikt Kriegesmann
Explicitly considering fail-safety within design optimization is computationally very expensive, since every possible failure has to be considered. This requires solving one finite element model per failure and iteration. In topology optimization, one cannot identify potentially failing structural members at the beginning of the optimization. Hence, a generic failure shape is applied to every possible location inside the design domain. In the current paper, the maximum stress is considered as optimization objective to be minimized,...

Unprecedented thermal stability of plasmonic titanium nitride films up to 1400 °C

Tobias Krekeler, Surya Snata Rout, Gnanavel Vaidhyanathan Krishnamurthy, Michael Störmer, Mahima Arya, Ankita Ganguly, Duncan S. Sutherland, Sergey Bozhevolnyi, Martin Ritter, Kjeld Pedersen, Alexander Petrov, Manfred Eich & Manohar Chirumamilla
Titanium nitride (TiN) has emerged as one of the most promising refractory materials for plasmonic and photonic applications at high temperatures due to its prominent optical properties along with mechanical and thermal stability. From a high temperature standpoint, TiN is a substitution for Au and Ag in the visible to near-infrared wavelength range, with potential applications including thermophotovoltaics, thermoplasmonics, hot-electron and high temperature reflective coatings. However, the optical properties and thermal stability of TiN films...

Probabilistic analysis of additively manufactured polymer lattice structures

Sven Drücker, Julian Kajo Lüdeker, Marvin Blecken, Arne Kurt, Kirill Betz, Benedikt Kriegesmann & Bodo Fiedler

Analysis of semi-open queueing networks using lost customers approximation with an application to robotic mobile fulfilment systems

Sonja Otten, Ruslan Krenzler, Lin Xie, Hans Daduna & Karsten Kruse
We consider a semi-open queueing network (SOQN), where one resource from a resource pool is needed to serve a customer. If on arrival of a customer some resource is available, the resource is forwarded to an inner network to complete the customer’s order. If no resource is available, the new customer waits in an external queue until one becomes available (“backordering”). When a resource exits the inner network, it is returned to the resource pool....

Evolution of length scales and of chemical heterogeneity during primary and secondary dealloying

Yong Li, Dinh Bao Nam Ngo, Jürgen Markmann & Jörg Weissmüller
We study the evolution of silver-rich regions, or ‘clusters’, during the making of nanoporous gold by dealloying. The clusters, which are remnants of the master alloy that have evaded corrosion, impact the functional behavior of the material. Furthermore, they carry information on the structure size in the initial stages of dealloying. Using kinetic Monte Carlo simulations, we emulate electrochemical dealloying at various electrode potentials. Our simulations illustrate the two-stage character of the process, where primary...

Subaqueous speleothems (Hells Bells) formed by the interplay of pelagic redoxcline biogeochemistry and specific hydraulic conditions in the El Zapote sinkhole, Yucatán Peninsula, Mexico

Simon Michael Ritter, Margot Isenbeck-Schröter, Christian Scholz, Frank Keppler, Johannes Gescher, Lukas Klose, Nils Schorndorf, Jerónimo Avilés Olguín, Arturo González-González & Wolfgang Stinnesbeck
Unique bell-shaped underwater speleothems were recently reported from the deep (∼ 55 m) meromictic El Zapote sinkhole (cenote) on the Yucatán Peninsula, Mexico. The local diving community has termed these speleothems as Hells Bells because of their shape and appearance in a dark environment in ∼ 28-38 m water depth above a sulfidic halocline. It was also suggested that Hells Bells form under water, yet the mystery of their formation remained unresolved. Therefore, we conducted...

Taylor bubble study of the influence of fluid dynamics on yield and selectivity in fast gas-liquid reactions

Felix Kexel, Alexandra von Kameke, Janina Tenhaus, Marko Hoffmann & Michael Schlüter
A consecutive competitive gas-liquid reaction is investigated using a Taylor bubble setup regarding the influence of fluid mixing in the bubble wake on yield and selectivity. The concentration fields behind a Taylor bubble are visualized and measured quantitatively with a novel time-resolved absorption imaging technique based on Beer Lamberts law and an integral selectivity is derived. In addition, the calculation of the local selectivity, often used in numerical approaches, is discussed and the existing experimental...

Thermal and thermoelastic problems in dry friction clutch: a comprehensive review

Nasr A. Jabbar, Ihsan Y. Hussain & Oday Ibraheem Abdullah
The friction clutch is considered a very important element of machines, as it plays a major role in transferring power from the driving part to the driven part. A common application of the friction clutch is in vehicles to connect between the gearbox and the engine. Fast wear occurs as a result of frictional heating that is generated when the clutch is starting to engage. This wear, in addition to the high thermal stresses, will...

Pre-deposited dynamic membrane adsorber formed of microscale conventional iron oxide-based adsorbents to remove arsenic from water : application study and mathematical modeling

Muhammad Usman, Aida Idrissi Belkasmi, Ioannis A. Kastoyiannis & Mathias Ernst
BACKGROUND: This study reports the development of a dynamic membrane (DM) adsorber by pre-depositing powdered-sizedfraction of iron oxide-based adsorptive material on the surface of a microfiltration(MF) membrane. The aim is to use the developed DM adsorber for arsenate (As(V)) remediation from water by a combined mechanism of adsorptive and membrane filtration. The two applied iron oxide-based adsorptive materials are micro-sized granular ferric hydroxide and micro-sized tetravalent manganese feroxyhyte, and are available at affordable price. RESULTS:...

Registration Year

  • 2021

Resource Types

  • Journal Article