17 Works

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...

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...

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...

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...

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...

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,...

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...

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...

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...

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)....

Finish machining of Ti6Al4V SLM components under consideration of thin walls and support structure removal

Wolfgang Hintze, Robert von Wenserski, Sebastian Junghans & Carsten Möller
Using additive manufacturing (AM) technologies such as powder bed based selective laser melting, it is possible to realize new bionic designs for Ti6Al4V aerospace components, thus significantly reducing weight. With these technologies, the goals of reducing emissions in the aviation industry can be achieved while passenger numbers are growing at the same time. In order to fulfill the quality requirements of the components, the AM process chain includes many further process steps in addition to...

Fast strategies in waiter-client games

Dennis Clemens, Pranshu Gupta, Fabian Hamann, Alexander Haupt, Mirjana Mikalački & Yannick Mogge
Waiter-Client games are played on some hypergraph (X,𝓕), where 𝓕 denotes the family of winning sets. For some bias b, during each round of such a game Waiter offers to Client b+1 elements of X, of which Client claims one for himself while the rest go to Waiter. Proceeding like this Waiter wins the game if she forces Client to claim all the elements of any winning set from 𝓕. In this paper we study...

OC6 Phase I: Investigating the underprediction of low-frequency hydrodynamic loads and responses of a floating wind turbine

Amy Robertson, Sébastien Gueydon, Erin E. Bachynski, Lu Wang, Jason Jonkman, D. Alarcón, Ervin Amet, Alec Beardsell, Paul Bonnet, B. Boudet, C. Brun, Zhen Chen, Marie Féron, Dominic Forbush, Christos Galinos, Josean Galvan, Philippe Gilbert, J. Gómez, V. Harnois, Florence Haudin, Z. Hu, Jean-Baptiste Le Dreff, Mareike Leimeister, Frank Lemmer, Haoran Li … & Svenja Wohlfahrt-Laymann
Phase I of the OC6 project is focused on examining why offshore wind design tools underpredict the response (loads/motion) of the OC5-DeepCwind semisubmersible at its surge and pitch natural frequencies. Previous investigations showed that the underprediction was primarily related to nonlinear hydrodynamic loading, so two new validation campaigns were performed to separately examine the different hydrodynamic load components. In this paper, we validate a variety of tools against this new test data, focusing on the...

Simulation of spray coating in a spouted bed using recurrence CFD

Paul Kieckhefen, Thomas Lichtenegger, Swantje Pietsch, Stefan Pirker & Stefan Heinrich
Although numerical models such as the computational fluid dynamics–discrete element method(CFD–DEM) have enabled the accurate simulation of laboratory-scale apparatuses, the application ofthese methods to large-scale apparatuses with many particles and time scales ranging from minutes tohours remains a challenge. The recently developed recurrence CFD (rCFD) method seeks to overcomethese issues in pseudo-periodic processes by extrapolating globally recurring patterns in a physicallymeaningful way and describing the transport and interaction of passive scalars using Lagrangian tracers.Spouted beds...

The influence of the void fraction on the particle migration: a coupled computational fluid dynamics–discrete element method study about drag force correlations

Manuela Kanitz & Jürgen Grabe
Granular soils subjected to flow through their soil skeleton can show a behaviour in which fine particles migrate through the pore space between coarser particles. This process is called internal instability or suffusion. This contribution deals with the numerical analysis of the migration of fine particles in a soil column subjected to fluid flow with unresolved coupled computational fluid dynamics–discrete element method (CFD–DEM) with special regards to the used drag force correlation. The contribution investigates...

Registration Year

  • 2020

Resource Types

  • Journal Article