@incollection{NosterAltenbergerRitchieetal., author = {Noster, Ulf and Altenberger, Igor and Ritchie, Robert O. and Scholtes, Berthold}, title = {Isothermal Fatigue Behavior and Residual Stress States of Mechanically Surface Treated Ti-6Al-4V: Laser Shock Peening vs. Deep Rolling}, series = {Shot peening}, booktitle = {Shot peening}, editor = {Wagner, Lothar}, publisher = {Wiley-VCH}, address = {Weinheim; [Cambridge]}, isbn = {9783527606580}, doi = {10.1002/3527606580.ch57}, pages = {447 -- 453}, abstract = {In this paper, the high-temperature fatigue behavior and residual stress states of a Ti-6Al-4V alloy are investigated after mechanical surface treatment. In particular, the two surface treatments investigated, laser shock peening and deep rolling, were observed to result in significantly different residual stress states. The consequent isothermal fatigue behavior at elevated temperatures, characterized using cyclic deformation curves, are discussed in terms of the stability of the near-surface work hardening and compressive residual stresses. Despite pronounced relaxation of the residual stresses, both laser shock peening and deep rolling led to a significant improvement in the cyclic deformation behavior and, hence, increased fatigue lifetimes at elevated temperatures as compared to untreated materials states.}, language = {en} } @inproceedings{Rill, author = {Rill, Georg}, title = {Real-Time capable Multibody Model of dual Truck Front Axles}, series = {Proceedings of DINAME 2023 - Selected Papers of the XIX International Symposium on Dynamic Problems of Mechanics, 26 Feb - 03 Mar 2023, Piren{\´o}polis, Brazil}, booktitle = {Proceedings of DINAME 2023 - Selected Papers of the XIX International Symposium on Dynamic Problems of Mechanics, 26 Feb - 03 Mar 2023, Piren{\´o}polis, Brazil}, editor = {Fleury, Agenor de T.}, publisher = {Springer}, abstract = {Dual front steering axles are quite common in multi-axled heavy duty trucks. In standard layouts of such axle combinations, the steer motions of the wheels depend not only on the rotation of the steering wheel but also on the movements of the axles. As a consequence, the model complexity of the steering system should match with the complexity of the suspension model. The development of new technologies like advanced driver assistance systems or autonomous driving can only be accomplished efficiently using extensive simulation methods. Such kind of applications demand for computationally efficient vehicle models. This paper presents a steering system model for dual front axles of heavy duty trucks which supplements the suspension model of the axles. The model takes the torsional compliance of the steering column as well as the stiffness of the tie rods and the coupling rod into account. A quasi-static solution provides a straight forward computation including the partial derivatives required for an efficient implicit solver. The steering system model matches perfectly with comparatively lean, but sufficiently accurate multibody suspension models.}, language = {en} } @inproceedings{SteiningerGadererDawoud, author = {Steininger, Peter and Gaderer, Matthias and Dawoud, Belal}, title = {Transient performance of a solar selective thermal insulation system}, series = {16th Advanced Building Skins Conference \& Expo, 21 - 22/10/2021, Bern, Switzerland}, booktitle = {16th Advanced Building Skins Conference \& Expo, 21 - 22/10/2021, Bern, Switzerland}, publisher = {Advanced Buidling Skins GmbH}, abstract = {A prototype of a thermal insulation system to offer high selectivity of the solar gain regarding the solar incidence angle (SATIS) was applied to a typical solid brick masonry for existing buildings in Germany. Light conducting elements (LCEs) inclined at 19 ° were incorporated in SATIS, which equals the average solar noon angle in southern Germany during winter. The entire wall construction was experimentally investigated in a differential climatic chamber test bench at four different irradiation angles according to a dynamic test procedure. In addition, a conventional wall construction (CWC) has been measured. At SATIS' design angle of 19 °, the SATIS wall construction shows a solar gain (SG) of 394.5 Wh/m², while the SG of the CWC amounts to only 25.4 Wh/m². The validated transient model of the SATIS wall construction showed that, at the end of the irradiation period of the dynamic test procedure (8 h), the solar heat penetrates to a depth of 253 mm and 111 mm inside the 385 mm thick brick wall masonry at the irradiation angles of 19 ° and 50 °, respectively. During the same time, the stored solar energy at 50 ° amounts to only 24.4 \% of that stored at 19 °.}, language = {en} } @incollection{AltenbergerNosterScholtesetal., author = {Altenberger, Igor and Noster, Ulf and Scholtes, Berthold and Ritchie, Robert O.}, title = {High Temperature Fatigue of Mechanically Surface Treated Materials}, series = {Shot peening}, booktitle = {Shot peening}, editor = {Wagner, Lothar}, publisher = {Wiley-VCH}, address = {Weinheim; [Cambridge]}, isbn = {9783527606580}, doi = {10.1002/3527606580.ch62}, pages = {483 -- 489}, abstract = {Introduction The most well known effect of mechanical surface treatments on metallic materials is the improvement in fatigue properties. It is therefore not surprising that most of the archival literature on mechanical surface treatments, such as shot peening, deep rolling and laser shock peening, deals with the effect of near-surface properties on fatigue behavior. Most of these studies, however, are confined to room temperature fatigue behavior; in comparision, the effect of mechanical surface treatment on fatigue behavior at high temperatures has been rarely investigated [1-5]. The reason for this disparity can be found in the popular belief that fatigue strength improvement by mechanical surface treatments is mainly due to the presence of compressive residual stresses, and since such stresses should anneal out at elevated temperatures, mechanical surface treatments for high temperature applications would appear questionable. However, this view may be over simplistic as there is always a possibility that the residual stresses may be at least partially stable at elevated temperatures [6]; in addition, other factors may be involved, such as the nature of the near-surface microstructure. Accordingly, it is the objective of this study to examine the role of mechanical surface treatments on the high temperature fatigue behavior of several metallic engineering materials. Moreover, it is the aim of this work to clarify what are the critical temperature "thresholds' at which near-surface microstructures and residual stresses become unstable and whether this can explain the observed fatigue behavior.}, language = {en} } @article{NallaAltenbergerNosteretal., author = {Nalla, Ravi K. and Altenberger, Igor and Noster, Ulf and Liu, G.Y. and Scholtes, Berthold and Ritchie, Robert O.}, title = {On the influence of mechanical surface treatments—deep rolling and laser shock peening—on the fatigue behavior of Ti-6Al-4V at ambient and elevated temperatures}, series = {Materials Science and Engineering: A}, volume = {355}, journal = {Materials Science and Engineering: A}, number = {1-2}, publisher = {Elsevier}, issn = {1873-4936}, doi = {10.1016/S0921-5093(03)00069-8}, pages = {216 -- 230}, abstract = {It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling (DR) is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of DR on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) behavior of a Ti-6Al-4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti-6Al-4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ∼450 °C, i.e. at a homologous temperature of ∼0.4T/Tm (where Tm is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy (TEM) observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti-6Al-4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti-6Al-4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment.}, language = {en} } @article{NosterScholtes, author = {Noster, Ulf and Scholtes, Berthold}, title = {Bauschingerefekt und mechanische Zwillingsbildung der Magnesiumlegierung AZ31}, series = {H{\"a}rterei-technische Mitteilungen : HTM ; Zeitschrift f{\"u}r Werkstoffe, W{\"a}rmebehandlung, Fertigung}, volume = {58}, journal = {H{\"a}rterei-technische Mitteilungen : HTM ; Zeitschrift f{\"u}r Werkstoffe, W{\"a}rmebehandlung, Fertigung}, publisher = {Hanser}, pages = {322 -- 327}, language = {de} } @article{HuberHeindlSchlosseretal., author = {Huber, Lea and Heindl, Melanie and Schlosser, Marc and Pfitzner, Arno and Dawoud, Belal}, title = {On the Cycle Stability and Macroscopic Structure of Iron Oxide Pellets for Thermochemical Hydrogen Storage: Influence of Water Content during the Pelletizing Process}, series = {Applied Sciences}, volume = {13}, journal = {Applied Sciences}, number = {11}, publisher = {MDPI}, address = {16}, doi = {10.3390/app13116408}, abstract = {Hydrogen storage based on the repeated reduction and oxidation (redox) reactions of iron oxide/iron composites represents a promising technology. This work is dedicated to studying the influence of the amount of water added during the pelletizing process on the cycle stability and structure of iron oxide pellets. The storage composites were prepared from iron oxide (Fe2O3) and 10 wt.-\% support material (cement) with different amounts of water (18 and 33 wt.-\%) in a laboratory-scale pelletizing disk. To evaluate the cycle stability of the composites, the kinetics of the redox reactions were experimentally measured at 800 ∘ C in an atmosphere of 50\% N2 and 50\% H2 (reduction) or 50\% steam (oxidation), respectively. Moreover, the structure of the pellets was analyzed by micro-computed tomography scans. It turned out that pellets with higher water contents attained faster kinetics and a higher cycle stability. The sample with the least water content (18 wt.-\%) needed about 26 min and 19 min to reach a conversion rate of 80\% during the reduction and oxidation reactions of the sixth redox cycle, respectively. In contrast, the sample with the highest water content (33 wt.-\%) could achieve the same conversion rate after 18 min (reduction) and 13 min (oxidation) during the ninth redox cycle.}, language = {en} } @misc{GradHahnNosteretal., author = {Grad, Marius and Hahn, Konstantin and Noster, Ulf and Spieß, Lothar}, title = {Increasing the lifetime of titanium implants through a diffusion-controlled surface treatment}, series = {Th{\"u}ringer Werkstofftag 2023, 14. M{\"a}rz 2023, ILmenau}, journal = {Th{\"u}ringer Werkstofftag 2023, 14. M{\"a}rz 2023, ILmenau}, doi = {10.13140/RG.2.2.35933.59360}, language = {en} } @article{KapsLehrerLepeniesetal., author = {Kaps, Arne and Lehrer, Tobias and Lepenies, Ingolf and Wagner, Marcus and Duddeck, Fabian}, title = {Multi-fidelity optimization of metal sheets concerning manufacturability in deep-drawing processes}, series = {Structural and Multidisciplinary Optimization}, volume = {66}, journal = {Structural and Multidisciplinary Optimization}, publisher = {Springer Nature}, doi = {10.1007/s00158-023-03631-8}, abstract = {Multi-fidelity optimization, which complements an expensive high-fidelity function with cheaper low-fidelity functions, has been successfully applied in many fields of structural optimization. In the present work, an exemplary cross-die deep-drawing optimization problem is investigated to compare different objective functions and to assess the performance of a multi-fidelity efficient global optimization technique. To that end, hierarchical kriging is combined with an infill criterion called variable-fidelity expected improvement. Findings depend significantly on the choice of objective function, highlighting the importance of careful consideration when defining an objective function. We show that one function based on the share of bad elements in a forming limit diagram is not well suited to optimize the example problem. In contrast, two other definitions of objective functions, the average sheet thickness reduction and an averaged limit violation in the forming limit diagram, confirm the potential of a multi-fidelity approach. They significantly reduce computational cost at comparable result quality or even improve result quality compared to a single-fidelity optimization.}, language = {en} } @article{SalamaKouDawoudetal., author = {Salama, Amgad and Kou, Jisheng and Dawoud, Belal and Rady, Mohamed and El Morshedy, Salah}, title = {Investigation of the self-propulsion of a wetting/nonwetting ganglion in tapered capillaries with arbitrary viscosity and density contrasts}, series = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, volume = {664}, journal = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, publisher = {Elsevier}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2023.131151}, abstract = {The movement of a meniscus inside a capillary tube has been extensively studied in the context of displacing one fluid with another immiscible one. This phenomenon exists in many applications including pharmaceutical, oil production, filtration and separation processes, and others. When one of the phases is entrapped inside a capillary tube, it forms what is called a ganglion with two menisci between the two fluids. In a straight uniform capillary tube, a stagnant entrapped ganglion is symmetric. The situation is different if the capillary tube is tapered in which case the two menisci assume different curvatures. Such inhomogeneity of the capillary pressure self-propels the ganglion to move. The fate of the ganglion inside the tapered tube depends on whether it is wetting or nonwetting to the tube wall. That is, after the initial movement, a wetting ganglion accelerates towards the tapered end of the tube while a nonwetting one decelerates towards the wider end before reaching a terminal configuration. Such fates are linked to the variations of the capillary pressure, which continuously increases for a wetting ganglion and decreases for the nonwetting one. In this work, a generalized model is developed that not only describes capillary-driven dynamics over a wide range of viscosity and density contrasts but also pressure-driven scenarios with/without gravity. The model, however, neglects the inertial effect of the two fluids on account of the fact that it is confined to the very early time of the movement process. A first-order nonlinear ordinary differential equation is developed that describes the dynamic behavior of both the wetting and nonwetting ganglions. A fourth-order Runge-Kutta algorithm is developed to solve the model equations. Furthermore, a computational fluid dynamics (CFD) analysis was used to provide a comparison and verification framework.}, language = {en} } @article{KoeckStrieglKrausetal., author = {K{\"o}ck, Hannah and Striegl, Birgit and Kraus, Annalena and Zborilova, Magdalena and Christiansen, Silke H. and Sch{\"a}fer, Nicole and Gr{\"a}ssel, Susanne and Hornberger, Helga}, title = {In Vitro Analysis of Human Cartilage Infiltrated by Hydrogels and Hydrogel-Encapsulated Chondrocytes}, series = {Bioengineering}, volume = {10}, journal = {Bioengineering}, publisher = {MDPI}, doi = {10.3390/bioengineering10070767}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-61235}, pages = {1 -- 21}, abstract = {Osteoarthritis (OA) is a degenerative joint disease causing loss of articular cartilage and structural damage in all joint tissues. Given the limited regenerative capacity of articular cartilage, methods to support the native structural properties of articular cartilage are highly anticipated. The aim of this study was to infiltrate zwitterionic monomer solutions into human OA-cartilage explants to replace lost proteoglycans. The study included polymerization and deposition of methacryloyloxyethyl-phosphorylcholine- and a novel sulfobetaine-methacrylate-based monomer solution within ex vivo human OA-cartilage explants and the encapsulation of isolated chondrocytes within hydrogels and the corresponding effects on chondrocyte viability. The results demonstrated that zwitterionic cartilage-hydrogel networks are formed by infiltration. In general, cytotoxic effects of the monomer solutions were observed, as was a time-dependent infiltration behavior into the tissue accompanied by increasing cell death and penetration depth. The successful deposition of zwitterionic hydrogels within OA cartilage identifies the infiltration method as a potential future therapeutic option for the repair/replacement of OA-cartilage extracellular suprastructure. Due to the toxic effects of the monomer solutions, the focus should be on sealing the OA-cartilage surface, instead of complete infiltration. An alternative treatment option for focal cartilage defects could be the usage of monomer solutions, especially the novel generated sulfobetaine-methacrylate-based monomer solution, as bionic for cell-based 3D bioprintable hydrogels.}, language = {en} } @article{WiesentStockerNonn, author = {Wiesent, Lisa and Stocker, Felix and Nonn, Aida}, title = {Investigating the influence of geometric parameters on the deformation of laser powder bed fused stents using low-fidelity thermo-mechanical analysis}, series = {Materialia}, volume = {28}, journal = {Materialia}, publisher = {Elsevier}, doi = {10.1016/j.mtla.2023.101774}, abstract = {Maintaining dimensional accuracy is a major challenge of laser powder bed fusion (L-PBF) preventing its application for more complex and filigree L-PBF structures in industrial practice. Previous studies have shown that residual stresses and distortion of benchmark L-PBF components may be predicted by sequential thermo-mechanical analyses. However, the reliability of these analyses for more complex structures must be critically questioned, as comprehensive validation and sensitivity analyses are scarce. In this paper, we present a calibrated and validated low-fidelity sequential thermo-mechanical finite element analysis (FEA) of a tubular L-PBF lattice structure, i.e., an aortic stent, where pronounced local deformation is expected. As a first step, the finite element model was extensively calibrated using experimental data to ensure reproducibility of the simulation results. Thereupon, geometric features critical to the distortion of L-PBF lattice structures and measures to compensate for the distortion, such as inversion of the distorted L-PBF structure, were investigated. It was found that the distortion of the L-PBF lattice structures can be reduced, but not completely prevented, by increasing the strut angles, increasing the strut thickness, and decreasing the transition radius in the area of merging struts. FEA-based inversion of the numerically predicted deformed structure minimized distortion, resulting in the L-PBF aortic stent approximating the intended CAD geometry even with a small strut thickness. This work shows that low-fidelity sequential thermo-mechanical FEA can be used not only for the analysis and deformation compensation of reference structures, but also for the analysis of more complex filigree structures with pronounced local deformation.}, language = {en} } @article{MikhaeilNowakPalombaetal., author = {Mikhaeil, Makram and Nowak, Sebastian and Palomba, Valeria and Frazzica, Andrea and Gaderer, Matthias and Dawoud, Belal}, title = {Experimental and analytical investigation of applying an asymmetric plate heat exchanger as an evaporator in a thermally driven adsorption appliance}, series = {Applied Thermal Engineering}, journal = {Applied Thermal Engineering}, number = {228}, publisher = {Elsevier}, doi = {10.1016/j.applthermaleng.2023.120525}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-61115}, abstract = {This communication presents an experimental and analytical study on the evaporation mechanism in a closed-structured asymmetric plate heat exchanger (PHE) employed as a stagnant water evaporator for the application in an adsorption heat transformation appliance. To this aim, an experimental unit is constructed, which comprises two identical PHEs, one acting as an vaporator/condenser and the second, as an adsorber/desorber. Two endoscopes are mounted inside the investigated evaporator to visualize the evaporation mechanism when performing adsorption-evaporation processes under different boundary conditions. It turned out that the evaporation mechanism is a partially covered, thin film evaporation. A heat transfer analysis is performed to evaluate the heat transfer coefficient of the thin film evaporation () inside the investigated evaporator, resulting in -values between 1330 and 160 [W∙m-2∙K-1] over the investigated adsorption-evaporation time. Correlating the obtained () to the film thickness and the wetted area results in -values between 0.34 and 0.78 [mm] and wetted to total area ratios of 0.78 to 0.16. Besides, an analytical model has been developed and introduced to correlate the overall evaporator heat transfer coefficient with the adsorption potential and the time rate of change of the water uptake.}, language = {en} } @article{ReindlMeisnerHierl, author = {Reindl, Thomas and Meisner, Dennis and Hierl, Stefan}, title = {Benchmarking of plastic-based Additive Manufacturing Processes}, series = {RTejournal - Forum f{\"u}r Rapid Technologie}, journal = {RTejournal - Forum f{\"u}r Rapid Technologie}, publisher = {Fachhochschule Aachen}, doi = {https://doi.org/10.58134/fh-aachen-rte_2023_002}, abstract = {Additive Manufacturing (AM) is a future-oriented manufacturing technology that is experiencing an enormous boom in the times of Industry 4.0. As a result, various AM technologies and printer models from different manufacturers are entering the market over a short time span. With the advancing establishment of this manufacturing technology for series applications, the expectations and requirements of the fabricated components are also increasing. However, a major challenge is the application-specific selection of the most suitable AM process due to a lack of comparable data. Furthermore, there needs to be more know-how regarding the geometrical and mechanical characteristics of AM parts. This paper addresses this problem by comparing the three most common plasticbased AM processes in the areas of surface quality, dimensional accuracy, and mechanical properties. Roughness measurements, evaluation of a benchmark artifact, tensile tests, and load increase tests are carried out. Based on the results, the individual possibilities and limitations of the compared AM processes can be detected.}, language = {en} } @unpublished{RillSchuderer, author = {Rill, Georg and Schuderer, Matthias}, title = {A Second Order Dynamic Friction Model Compared to Commercial Stick-Slip Models}, doi = {10.20944/preprints202306.1233.v1}, abstract = {Friction has long been an important issue in multibody dynamics. Static friction models apply appropriate regularization techniques to convert the stick inequality and the non-smooth stick-slip transition of Coulomb's approach into a continuous and smooth function of the sliding velocity. However, a regularized friction force is not able to maintain long-term stick. That is why, dynamic friction models were developed in the last decades. The friction force depends herein not only on the sliding velocity but also on internal states. The probably best known representative, the LuGre friction model, is based on a fictitious bristle but realizes a too simple approximation. The recently published second order dynamic friction model describes the dynamics of a fictitious bristle more accurately. Its performance is compared here to stick-slip friction models, developed and launched not long ago by commercial multibody software packages.}, language = {en} } @book{RillSchaefferBorchsenius, author = {Rill, Georg and Schaeffer, Thomas and Borchsenius, Fredrik}, title = {Grundlagen und computergerechte Methodik der Mehrk{\"o}rpersimulation}, publisher = {Springer Nature}, doi = {10.1007/978-3-658-41968-4}, pages = {XIV, 260}, abstract = {Dieses Lehr- und {\"U}bungsbuch vermittelt auf anschauliche Weise die Methoden der Mehrk{\"o}rpersimulation und verdeutlicht deren Vor- und Nachteile bei der praktischen Anwendung anhand konkreter Beispiele. Die einzelnen Methoden werden durch Matlab-Skripte und -Funktionen verdeutlicht, wobei die Modellbildung, die mathematische Beschreibung und die numerische Simulation von Systemen starrer K{\"o}rper die Schwerpunkte bilden. Die vorliegende Auflage wurde unter anderem um Matlab-Live-Skripte erweitert, welche kleine Animationen zur Veranschaulichung der Dynamik der Probleme enthalten. Die L{\"o}sungen zu den {\"U}bungsbeispielen und die integrierten Matlab-Skripte sowie weitere Beispiele und Anwendungen stehen {\"u}ber QR-Codes zum Download zur Verf{\"u}gung und erm{\"o}glichen dadurch auch ein effizientes Selbststudium.}, subject = {Mehrk{\"o}rpersystem}, language = {de} } @incollection{RillSchaefferBorchsenius, author = {Rill, Georg and Schaeffer, Thomas and Borchsenius, Fredrik}, title = {Analyse von Mehrk{\"o}rpersystemen}, series = {Grundlagen und computergerechte Methodik der Mehrk{\"o}rpersimulation}, booktitle = {Grundlagen und computergerechte Methodik der Mehrk{\"o}rpersimulation}, publisher = {Springer}, doi = {10.1007/978-3-658-41968-4_5}, pages = {198}, abstract = {Nach dem Aufbau eines Mehrk{\"o}rper-Simulationsmodells muss dieses auf Richtigkeit, Funktionalit{\"a}t und Wirtschaftlichkeit getestet werden. Die Ermittlung der Gleichgewichtslage stellt dabei eine erste Plausibilit{\"a}ts-Kontrolle dar. Eine Linearisierung mit anschließender Analyse der Eigendynamik liefert Aussagen {\"u}ber die Frequenzen und das D{\"a}mpfungsverhalten des Modells. Einfache Erregersignale erm{\"o}glichen einen ersten Einblick in das nichtlineare dynamische Verhalten des Modells. Modell-Parameter, die nicht genau bekannt sind, k{\"o}nnen durch gezielte Variationen plausibel gesch{\"a}tzt oder {\"u}ber eine Optimierung sogar mit optimalen Werten belegt werden. Nach all diesen Tests steht das Mehrk{\"o}rper- Simulationsmodell dann f{\"u}r praktischeUntersuchungen zurVerf{\"u}gung, die neben reinen Zeitsimulationen auch Methoden der Inversen Kinematik und der Inversen Dynamik mit einschließen.}, language = {de} } @inproceedings{SchneidewindGalka, author = {Schneidewind, Jan and Galka, Stefan}, title = {Interactive reinforcement learning-based factory layout planning}, series = {13th Conference on Learning Factories (CLF 2023), 9-11 May 2023, Reutlingen, Germany}, booktitle = {13th Conference on Learning Factories (CLF 2023), 9-11 May 2023, Reutlingen, Germany}, publisher = {SSRN}, pages = {6}, abstract = {Due to the complexity and the number of factors involved in factory layout planning, computers were identified as an efficient tool to support the process. However, so far no method for computer-aided layout planning has gained wide acceptance in practical application. One reason for this is that in present approaches either the user or the computer designs the layout, neglecting either the qualitative or the quantitative goals. To bridge this gap, this article introduces a concept for human-computer-integration based on evaluative feedback and inverse reinforcement learning. A key element of the concept is the interactive planning process in which user and computer alternately design and improve the layout until a satisfactory layout is found. The user evaluates the layouts according to qualitative criteria, adjusts them intuitively and specifies objectives and restrictions in an explorative way. The computer on the other hand - in form of a reinforcement algorithm - generates possible layouts and incorporates the user's feedback into its policy. This synergy is expected to generate better results than an expert or an algorithm alone could. Furthermore, in the context of learning factories, it encourages critical thinking and allows students to develop a deeper understanding of the factors that contribute to efficient manufacturing processes. Both an architecture for the implementation is proposed and the requirements for the user interface are specified.}, language = {en} } @inproceedings{RiegervandeParRabletal., author = {Rieger, Anna and van de Par, Steven and Rabl, Hans-Peter and Oetjen, Arne}, title = {Ein Ton macht noch keine Harmonie - Der Einfluss von Tonhaltigkeit und Dissonanz auf Pr{\"a}ferenzurteile}, series = {Fortschritte der Akustik - DAGA 2023, 49. Jahrestagung f{\"u}r Akustik, 06.-09. M{\"a}rz 2023 in Hamburg}, booktitle = {Fortschritte der Akustik - DAGA 2023, 49. Jahrestagung f{\"u}r Akustik, 06.-09. M{\"a}rz 2023 in Hamburg}, publisher = {Deutsche Gesellschaft f{\"u}r Akustik e.V. (DAGA)}, address = {Berlin}, isbn = {978-3-939296-21-8}, pages = {1167 -- 1170}, abstract = {Produkt- bzw. Maschinenger{\"a}usche mit deutlich h{\"o}rbaren tonalen Komponenten werden h{\"a}ufig als l{\"a}stig empfunden. Wenn zus{\"a}tzlich eine Interaktion mehrerer tonaler Komponenten in Ger{\"a}uschen stattfindet, was in realen Szenarien beispielsweise durch die {\"U}berlagerung tonaler Komponenten durch verschiedene Aggregate, wie Motoren und Getrieben, stattfindet, dann k{\"o}nnen Ger{\"a}usche unterschiedlich tonal, aber auch unterschiedlich konsonant und dissonant wahrgenommen werden. Vorangehende H{\"o}rexperimente haben gezeigt, dass die Dissonanz bei {\"a}hnlicher Tonhaltigkeit der Ger{\"a}usche einen großen Einfluss auf die Pr{\"a}ferenzurteile hat. Des Weiteren konnte bereits ein grundlegendes Empfindungsmodell f{\"u}r die "Dissonanz" sowie ein Pr{\"a}ferenz-Pr{\"a}diktor entwickelt werden, die die Subjektivdaten in hoher G{\"u}te vorhersagen konnten. In den hier vorgestellten Versuchen wurde das Zusammenspiel zwischen der empfundenen Tonhaltigkeit und der sich aus mehreren Tonkomponenten ergebenden Dissonanz auf die Pr{\"a}ferenzurteile untersucht. In der Analyse wird aufgezeigt, auf welche Weise und in welchem Umfang die wahrgenommene Ausgepr{\"a}gtheit der Tonhaltigkeit durch Interaktion mehrerer Tonkomponenten die allgemeine Ger{\"a}uschqualit{\"a}t beeinflusst. Da verschiedene Grade der Dissonanz nur durch die gleichzeitige Anwesenheit tonaler Komponenten entstehen k{\"o}nnen, ist das Zusammenspiel beider Gr{\"o}ßen bei der Bildung eines Pr{\"a}ferenzurteils von einer speziellen Natur. Dies wird sowohl bei der Modellierung der Interaktion beider Gr{\"o}ßen als auch im Vorhersagemodell der Dissonanz ber{\"u}cksichtigt.}, language = {de} } @inproceedings{Fuhrmann, author = {Fuhrmann, Thomas}, title = {Semi-Structured Lab Projects in Communication Engineering Education}, series = {2023 IEEE Global Engineering Education Conference (EDUCON), 01-04 May 2023, Kuwait}, booktitle = {2023 IEEE Global Engineering Education Conference (EDUCON), 01-04 May 2023, Kuwait}, publisher = {IEEE}, doi = {10.1109/EDUCON54358.2023.10125244}, pages = {1 -- 5}, abstract = {It is generally known that project-based learning is a very important part of engineering education to connect theoretical knowledge with practical work. Students learn to apply their knowledge to real-world challenges as it is the case in their later professional life. If students are not used to project work or the scientific topic is new and relatively complex, they may be overwhelmed. The consequence is that students achieve poor results, are frustrated, and therefore learning success is low. Semi-structured projects are introduced that combine the advantages of structured experiments with projects. The project work is structured into several parts with detailed descriptions of the tasks. In the end, students get similar results to doing a free project, but the success rate is higher due to higher guidance. Therefore, these semi-structured projects are seen to be an appropriate method to guide students to learn how to do project work. The feedback from most students is very positive. Some students with no previous lab experience complained about the project work and wished for more guidance to become familiar with lab work. In sum, the student feedback is encouraging to develop semi-structured projects further.}, language = {en} } @inproceedings{JudenmannHoltmannspoetterEhrlich, author = {Judenmann, Anna and Holtmannsp{\"o}tter, Jens and Ehrlich, Ingo}, title = {Additive Manufacturing of Continuous Fiber-Reinforced Composites}, series = {Proceedings of the Munich Symposium on Lightweight Design 2022}, booktitle = {Proceedings of the Munich Symposium on Lightweight Design 2022}, language = {de} } @article{GebhardtSchlampEhrlichetal., author = {Gebhardt, Jakob and Schlamp, Matthias and Ehrlich, Ingo and Hiermaier, Stefan}, title = {Low-velocity impact behavior of elliptic curved composite structures}, series = {International Journal of Impact Engineering}, volume = {180}, journal = {International Journal of Impact Engineering}, publisher = {Elsevier}, doi = {10.1016/j.ijimpeng.2023.104663}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-59304}, pages = {8}, abstract = {Although many composite structures are inconsistently curved, such as the leading edges of aircraft wings, the variety of research in impact engineering is almost limited to the impact performance of plates or cylindrically curved specimens. It is not known whether the findings obtained from standardized tests can be transferred to curved structures or which adaptions are required. Therefore, a deeper understanding of the deformation and damage behavior of inconsistently curved structures is essential to transfer the observed impact behavior of flat specimens to general curved structures and therefore to utilize the full lightweight potential of a load-specific design. An accurate description of the procedure as well as the results of the experimental and numerical study of the low-velocity impact behavior of differently single-curved elliptic specimens is presented. To close the research gap of the impact behavior of geometries with curvatures between the plates and simplified leading edges, novel specimens geometries have been derived from established impact test standards. Glassfiber-reinforced specimens are subjected to an instrumented impact test at constant impact energy. This is numerically investigated by a stacked-layer model, which used cohesive zone modeling to enable the simulation of matrix cracking, fiber fracture and delamination. The resulting projected damage areas, as well as the force and deflection histories, were evaluated and section cuts were examined to discuss the damage morphology, formation and propagation process. Significant effects on maximum deflection, compliance and dynamic behavior on the size and morphology of damage were found.}, language = {en} } @inproceedings{GerschSchulz, author = {Gersch, Sebastian and Schulz, Carsten}, title = {Realpotential von Eigenspannungen zur Erh{\"o}hung der Bauteillebensdauer bei generativ gefertigten, dynamisch beanspruchten Bauteilen}, series = {Dresdner Maschinenelemente Kolloquium - DMK 2022, 26.-27. April / Technische Universit{\"a}t Dresden}, booktitle = {Dresdner Maschinenelemente Kolloquium - DMK 2022, 26.-27. April / Technische Universit{\"a}t Dresden}, publisher = {sierke Verlag}, address = {G{\"o}ttingen}, isbn = {978-3-96548-135-0}, pages = {496 -- 505}, language = {de} } @inproceedings{SchaefferHerrmannBoehm, author = {Schaeffer, Leon and Herrmann, David and B{\"o}hm, Valter}, title = {Preliminary theoretical considerations of a hand orthosis based on a prestressed, compliant structure}, series = {Proceedings of the 2023 International Symposium on Medical Robotics (ISMR), Atlanta, 19-21 April 2023}, booktitle = {Proceedings of the 2023 International Symposium on Medical Robotics (ISMR), Atlanta, 19-21 April 2023}, publisher = {IEEE}, doi = {10.1109/ISMR57123.2023.10130230}, pages = {1 -- 7}, abstract = {In the treatment of hand injuries in the context of orthopedic care, movable hand orthoses are used in many cases. Early motion therapy is in most cases advantageous for adequate, rapid, and successful long-term healing of the hand. Conventional mobile hand orthoses can only be used for movement therapy to a limited extent since they represent the wrist as a simple rotating joint and neglect the complexity of the movement possibilities of the hand. In this paper, a novel concept for movable hand orthoses based on prestressed compliant structures is presented. The advantage with this concept is that it replicates the multiaxial motion capabilities without the need for conventional joints. Besides the derivation and description of the concept, a first three-dimensional CAD design is shown. Additionally, the next planned steps in the development of such a novel dynamic hand orthosis are described.}, language = {en} } @inproceedings{SchaefferHerrmannBoehm, author = {Schaeffer, Leon and Herrmann, David and B{\"o}hm, Valter}, title = {Concept of a wrist Hand Orthosis based on a prestressed compliant structure}, series = {Proceedings of the 7th International Conference on Biomedical Engineering and Applications (ICBEA), Hangzhou, China, 21-23 April 2023}, booktitle = {Proceedings of the 7th International Conference on Biomedical Engineering and Applications (ICBEA), Hangzhou, China, 21-23 April 2023}, publisher = {IEEE}, doi = {10.1109/ICBEA58866.2023.00024}, pages = {98 -- 103}, abstract = {In the treatment of hand injuries in the context of orthopedic care, movable wrist hand orthoses are used in numerous instances. Early motion therapy is in most cases advantageous for adequate, rapid and successful long-term healing of the hand. Conventional dynamic wrist hand orthoses can only be used for movement therapy to a limited extent since they represent the wrist as a simple rotating joint and neglect the complexity of the hand movement possibilities. In this paper, a preliminary concept for dynamic wrist hand orthoses based on prestressed compliant structures is presented. The distinctive feature of this concept lies in the enabling of multiaxial motion capabilities of the human hand without applying conventional joints. According to the concept the wrist region is surrounded by a prestressed compliant structure. Besides the derivation and description of the concept, a first three-dimensional computer-aided design is shown. Additionally, the necessary steps in the development of such a novel dynamic wrist orthosis are discussed.}, language = {en} } @inproceedings{StelzerTauwaldVielsmeieretal., author = {Stelzer, Vera and Tauwald, Sandra Melina and Vielsmeier, Veronika and Cieplik, Fabian and Kandulski, Arne and Schneider-Brachert, Wulf and W{\"u}nsch, Olaf and R{\"u}tten, Markus and Krenkel, Lars}, title = {Generation and Distribution of Surgical Smoke During High Frequency Electrocauterization}, series = {New Results in Numerical and Experimental Fluid Mechanics XIV. STAB/DGLR Symposium 2022}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XIV. STAB/DGLR Symposium 2022}, editor = {Dillman, Andreas and Heller, Gerd and Kraemer, Ewald and Wagner, Claus and Weiss, Julien}, publisher = {Springer Nature Switzerland AG}, address = {Cham, Switzerland}, isbn = {978-3-031-40481-8}, doi = {10.1007/978-3-031-40482-5_53}, pages = {559 -- 568}, abstract = {Surgical Smoke is generated during the cauterization of tissue with high-frequency (HF) devices and consists of 95\% water vapor and 5\% cellular debris. When the coagulation tweezers, which are supplied with HF voltage by the HF device, touch tissue, the electric circuit is closed, and smoke is generated by the heat. In-vivo investigations are performed during tracheotomies where surgical smoke is produced during coagulation of tissue. Furthermore, in-vitro parametric studies to investigate the particle number and size distribution and the spatial distribution of surgical smoke with laser light sheet technique are conducted. With higher power of the HF device, the particles generated are larger in size and the total number of particles generated is also higher. Adding artificial saliva to the tissue shows even higher particle counts. The study by laser light sheet also confirms this. The resulting characteristic size distribution, which may include viruses and bacterial components, confirms considering the risk arising from surgical smoke. Furthermore, the experiments will provide the database for further numerical investigations.}, language = {en} } @inproceedings{TauwaldQuadrioRuettenetal., author = {Tauwald, Sandra Melina and Quadrio, Maurizio and R{\"u}tten, Markus and Stemmer, Christian and Krenkel, Lars}, title = {High Spatial Resolution Tomo-PIV of the Trachea Focussing on the Physiological Breathing Cycle}, series = {New Results in Numerical and Experimental Fluid Mechanics XIV - Contributions to the 23nd STAB/DGLR Symposium}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XIV - Contributions to the 23nd STAB/DGLR Symposium}, publisher = {Springer}, abstract = {Investigations of complex patient-specific flow in the nasopharynx requires high resolution numerical calculations validated by reliable experiments. When building the validation base and the benchmark of computational fluid dynamics, an experimental setup of the nasal airways was developed. The applied optical measurement technique of tomo-PIV supplies information on the governing flow field in three dimensions. This paper presents tomo-PIV measurements of the highly complex patient-specific geometry of the human trachea. A computertomographic scan of a person's head builds the basis of the experimental silicone model of the nasal airways. An optimised approach for precise refractive index matching avoids optical distortions even in highly complex non-free-of-sight 3D geometries. A linear-motor-driven pump generates breathing scenarios, based on measured breathing cycles. Adjusting of the CCD cameras' double-frame-rate PIV-Δt enables the detailed analysis of flow structures during different cycle phases. Merging regions of interest enables high spatial resolution acquisition of the flow field.}, language = {en} } @article{ReinkerDendorfer, author = {Reinker, Lukas and Dendorfer, Sebastian}, title = {Evaluation of acceleration patterns during high-impact jumping exercises}, series = {Gait \& Posture}, volume = {100}, journal = {Gait \& Posture}, number = {Supplement 1, March}, publisher = {Elsevier}, address = {Amsterdam [u.a.]}, doi = {10.1016/j.gaitpost.2022.11.051}, pages = {93 -- 94}, language = {en} } @misc{BirkenmaierKrenkelLehle, author = {Birkenmaier, Clemens and Krenkel, Lars and Lehle, Karla}, title = {Linking flow conditions in membrane oxygenators to arrangements of multimeric von-Willebrand-factor as indication for coagulation}, series = {World Congress of Biomechanics 2018, Convention Centre Dublin, 8.-12. Juli 2018}, journal = {World Congress of Biomechanics 2018, Convention Centre Dublin, 8.-12. Juli 2018}, abstract = {Introduction Shear induced multimerisation of von-Willebrand-factor (vWF) is supposed to play an important role in coagulation inside extracorporeal membrane oxygenators. However, there is no proof that links observed vWF structures to computed or measured flow conditions. Methods The structures of multimeric vWF fibers, observed in clinically used membrane oxygenators is examined using immunofluorescence microscopy (IFM) using Carstairs' staining method (positive ethics committee vote). The flow around the membrane fibres inside the oxygenator is investigated in terms of shear rate, wall shear velocity and streamlines by using CFD (RANS, Carreau-Yasuda viscosity, geometry remodelled after high-resolution µCT-scans). By interpreting the histological and numerical results in this common context, indications for shear induced coagulation mechanisms can be identified. Results The fibre structures of multimeric vWF build regular but not exactly symmetric formations around the contact face (CF) between the crosswise stacked oxygenator fibres (OF), see fig.1B, vWF marked red. Annular around the CF arranged, cells are likely to be found, see fig.1B, nuclei marked blue. The computed streamlines around the OF show attached flow around the circular fibres. However, the irregular arrangement of real OF produce considerable cross flow between the interconnected neighbouring channels, in contrast to previous 2D-simulations. Thus, the CF are washed around closely by blood, also from neighbouring channels. The wall shear velocity streamlines form regular, slightly asymmetric shapes around the contact faces. The occurring maximum shear rates are in the range of 1,000 1/s. Discussion The shapes of vWF structures found in clinically used oxygenators match the computational results in terms of wall shear velocity and streamlines well. The accumulation of cells close to the CF can also be explained by fluid mechanics, as there are small shear gradients and slow velocities. However, occurring shear rates between OFs are too low to trigger multimerisation of vWF. That raises the question where in the circuit the actual activation of vWF is started and how, at least partly chained, vWF multimeres are attracted towards the OF surface. A next step will be the investigation of the actual shear rate triggered (or mediated) multimerisation of vWF. Towards this end, microfluidic experiments with shear triggered coagulation will be performed. Also of big interest is the computation of the flow situation in the oxygenator in proximity to chaining threads, which have been ignored in computations so far. However, first a realistic representation of the effective viscosity in computations is needed, which is not available yet.}, language = {en} } @inproceedings{GalkaSchuhegger, author = {Galka, Stefan and Schuhegger, Lukas}, title = {Integration of Discrete-event Simulation in the Planning of a Hydrogen Electrolyzer Production Facility}, series = {Proceedings of the 2022 Winter Simulation Conference (WSC), 11-14 Dec. 2022, Singapore}, booktitle = {Proceedings of the 2022 Winter Simulation Conference (WSC), 11-14 Dec. 2022, Singapore}, editor = {Feng, B. and Pedrielli, G. and Peng, Y. and Shashaani, S. and Song, E. and Corlu, C.G. and Lee, L.H. and Chew, E.P. and Roeder, T. and Lendermann, P.}, publisher = {IEEE}, address = {Singapore}, pages = {2}, abstract = {In the context of production and factory planning, the expansion of the factory must already be taken into account during initial planning. This results in an increase in planning complexity, as the involved planners have to know the expansion stages of the factory in the different time periods and have to evaluate concept modifications across all time periods. This paper presents an idea for a planning tool, which takes expansion stages into consideration. The data model contains all relevant information to generate a simulation model of the factory in an almost automated way. The aim is to enable factory planners to quickly investigate concept changes with the help of simulation, for example, to identify bottlenecks.}, language = {en} } @misc{WildGalkaWappleretal., author = {Wild, Tobias and Galka, Stefan and Wappler, Mona and Xing, Lu}, title = {Integrating supply chain aspects into factory planning, a simulation approach}, series = {The journey to sustainable supply chains: proceedings of the 26th International Symposium on Logistics (ISL 2022), 10-13th July 2022, Cork, Ireland}, journal = {The journey to sustainable supply chains: proceedings of the 26th International Symposium on Logistics (ISL 2022), 10-13th July 2022, Cork, Ireland}, editor = {Potter, A. and Pawar, K. S. and O'Reilly, S. and Jimo, A.}, publisher = {Nottingham University Business School, UK}, address = {Nottingham, UK}, isbn = {978-0-85358-350-9}, pages = {6}, abstract = {One major goal of green-field factory planning is to decide on space requirements in the plant. In this phase, detailed information about the supply chain network (e.g. which suppliers deliver which parts) is often unavailable. Nevertheless, typical decisions in supply chain management, like the definition of replenishment processes and quantities or make-or-buy decisions, impact space requirements in the factory and should therefore be considered in the factory planning. This research article proposes a simulation approach for a factory simulation in which raw material replenishment is integrated to evaluate the space requirements for raw materials.}, language = {de} } @inproceedings{HaimerlTschernitzSchilleretal., author = {Haimerl, Simon and Tschernitz, Christoph and Schiller, Tobias and Weig, Christoph and Briem, Ulrich and Galka, Stefan}, title = {Development of a Simulation Framework for Urban Ropeway Systems and Analysis of the Planned Ropeway Network in Regensburg, Germany}, series = {Proceedings of the 2022 Winter Simulation Conference (WSC), 11-14 Dec. 2022, Singapore}, booktitle = {Proceedings of the 2022 Winter Simulation Conference (WSC), 11-14 Dec. 2022, Singapore}, publisher = {IEEE}, isbn = {978-1-6654-7661-4}, doi = {10.1109/WSC57314.2022.10015510}, pages = {1413 -- 1424}, abstract = {To evaluate the performance of a ropeway in an urban environment, simulations of the dynamic passenger transport characteristics are required. Therefore, a modular simulation model for urban ropeway networks was developed, which can be flexibly adapted to any city and passenger volume. This simulation model was used to analyze the ropeway network concept of the German city Regensburg and to determine the expected operating conditions. The passenger volume, different types of persons, their occurrence probability and their destination distribution is depending on the location and daytime and can be defined for each individual station. In an initial analysis, the number of passengers currently occurring in bus traffic were projected onto the ropeway network. To enable climate-friendly and efficient operation, different strategies were developed to significantly reduce the number of gondolas. The best fitting strategies resulted in significant cost savings while passenger comfort, as represented by queue time, remained unchanged.}, language = {en} } @inproceedings{SchmidWildSchneidewindetal., author = {Schmid, Florian and Wild, Tobias and Schneidewind, Jan and Vogl, Tobias and Schuhegger, Lukas and Galka, Stefan}, title = {Simulation Based Approach for Reconfiguration and Ramp up Scenario Analysis in Factory Planning}, series = {Proceedings of the 2022 Winter Simulation Conference (WSG), 11-14 Dec. 2022, Singapore}, booktitle = {Proceedings of the 2022 Winter Simulation Conference (WSG), 11-14 Dec. 2022, Singapore}, publisher = {IEEE}, isbn = {978-1-6654-7661-4}, doi = {10.1109/WSC57314.2022.10015310}, pages = {2842 -- 2852}, abstract = {Structural changes in production entail a potential economic risk for manufacturing companies. It is necessary to identify a suitable strategy for the reconfiguration process and to continue to meet the demand during the change in the factory structure and ramp-up phase. A simulation offers the possibility to analyze different ramp-up scenarios for the factory structure and to select a suitable concept for the reconfiguration process. A discrete event simulation approach is presented that can be used to evaluate variants of structural changes and serves as a basis for deciding on a reconfiguration strategy. This approach is demonstrated using a specific production step of a plant producing hydrogen electrolyzers, the results and generalized conclusions are discussed.}, language = {en} } @misc{KoeglerIsmailRusavyetal., author = {K{\"o}gler, Michael and Ismail, Khaled M. and Rusavy, Zdenek and Kalis, Vladimir and S{\"u}ß, Franz and Dendorfer, Sebastian}, title = {Influence of bed height and stance on accoucheurs lower back and glenohumeral load during simulated childbirth}, series = {31st meeting of Czech Urogynaecological Society, Prague, 2022}, journal = {31st meeting of Czech Urogynaecological Society, Prague, 2022}, language = {en} } @article{DendorferMelzner, author = {Dendorfer, Sebastian and Melzner, Maximilian}, title = {R{\"u}ckenschmerzen bei Geburtshelfer:innen. Die Haltung macht's.}, series = {Deutsche Hebammen-Zeitschrift}, volume = {74}, journal = {Deutsche Hebammen-Zeitschrift}, number = {11}, publisher = {Staude}, address = {Hannover}, issn = {0012-026X}, pages = {60 -- 62}, abstract = {F{\"u}r Mutter und Kind konnte das Risiko der Geburt durch die Weiterentwicklung der Medizin drastisch reduziert werden. Doch wie ist es um das Wohl derer bestellt, die die Geb{\"a}rende unterst{\"u}tzen? Eine Studie der Ostbayerischen Technischen Hochschule Regensburg hat sich mit den muskuloskelettalen Beschwerden von Geburtshelfer:innen auseinandergesetzt}, language = {de} } @article{ReinkerBlaesingBierletal., author = {Reinker, Lukas and Bl{\"a}sing, Dominic and Bierl, Rudolf and Ulbricht, Sabina and Dendorfer, Sebastian}, title = {Correlation of Acceleration Curves in Gravitational Direction for Different Body Segments during High-Impact Jumping Exercises}, series = {sensors}, volume = {23}, journal = {sensors}, number = {4}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/s23042276}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-58217}, abstract = {Osteoporosis is a common disease of old age. However, in many cases, it can be very well prevented and counteracted with physical activity, especially high-impact exercises. Wearables have the potential to provide data that can help with continuous monitoring of patients during therapy phases or preventive exercise programs in everyday life. This study aimed to determine the accuracy and reliability of measured acceleration data at different body positions compared to accelerations at the pelvis during different jumping exercises. Accelerations at the hips have been investigated in previous studies with regard to osteoporosis prevention. Data were collected using an IMU-based motion capture system (Xsens) consisting of 17 sensors. Forty-nine subjects were included in this study. The analysis shows the correlation between impacts and the corresponding drop height, which are dependent on the respective exercise. Very high correlations (0.83-0.94) were found between accelerations at the pelvis and the other measured segments at the upper body. The foot sensors provided very weak correlations (0.20-0.27). Accelerations measured at the pelvis during jumping exercises can be tracked very well on the upper body and upper extremities, including locations where smart devices are typically worn, which gives possibilities for remote and continuous monitoring of programs.}, language = {en} } @inproceedings{SchulzKiessGraness, author = {Schulz, Carsten and Kieß, Benjamin and Graneß, Henry}, title = {Tooth root modeling induced variations of the calculated transmission error}, series = {NAFEMS World Congress, Tampa, 15th-18th May 2023}, booktitle = {NAFEMS World Congress, Tampa, 15th-18th May 2023}, language = {en} } @misc{SchudererRillSchaefferetal., author = {Schuderer, Matthias and Rill, Georg and Schaeffer, Thomas and Schulz, Carsten}, title = {Friction modeling from a practical point of view}, series = {MULTIBODY2023: 11th ECCOMAS Thematic Conference on Multibody Dynamics, Tampa, 24th-28th May 2023}, journal = {MULTIBODY2023: 11th ECCOMAS Thematic Conference on Multibody Dynamics, Tampa, 24th-28th May 2023}, language = {en} } @article{GamischHuberGadereretal., author = {Gamisch, Bernd and Huber, Lea and Gaderer, Matthias and Dawoud, Belal}, title = {On the Kinetic Mechanisms of the Reduction and Oxidation Reactions of Iron Oxide/Iron Pellets for a Hydrogen Storage Process}, series = {Energies}, volume = {15}, journal = {Energies}, number = {21}, publisher = {MDPI}, doi = {10.3390/en15218322}, abstract = {This work aims at investigating the kinetic mechanisms of the reduction/oxidation (redox) reactions of iron oxide/iron pellets under different operating conditions. The reaction principle is the basis of a thermochemical hydrogen storage system. To simulate the charging phase, a single pellet consisting of iron oxide (90\% Fe2O3, 10\% stabilising cement) is reduced with different hydrogen (H2) concentrations at temperatures between 600 and 800 °C. The discharge phase is initiated by the oxidation of the previously reduced pellet by water vapour (H2O) at different concentrations in the same temperature range. In both reactions, nitrogen (N2) is used as a carrier gas. The redox reactions have been experimentally measured in a thermogravimetric analyser (TGA) at a flow rate of 250 mL/min. An extensive literature review has been conducted on the existing reactions' kinetic mechanisms along with their applicability to describe the obtained results. It turned out that the measured kinetic results can be excellently described with the so-called shrinking core model. Using the geometrical contracting sphere reaction mechanism model, the concentration- and temperature-dependent reduction and oxidation rates can be reproduced with a maximum deviation of less than 5\%. In contrast to the reduction process, the temperature has a smaller effect on the oxidation reaction kinetics, which is attributed to 71\% less activation energy (Ea,Re=56.9 kJ/mol versus Ea,Ox=16.0 kJ/mol). The concentration of the reacting gas showed, however, an opposite trend: namely, to have an almost twofold impact on the oxidation reaction rate constant compared to the reduction rate constant.}, language = {en} } @misc{WagnerKrenkelDoenitzetal., author = {Wagner, Thomas and Krenkel, Lars and D{\"o}nitz, Christian and Brawanski, Alexander}, title = {Influence of CFD Strategy on WSS and OSI Determination for Intracranial Aneurysm Rupture Assessment}, series = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, journal = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, language = {en} } @misc{TauwaldKrenkel, author = {Tauwald, Sandra Melina and Krenkel, Lars}, title = {Elementary experimental setup for flow visualization in upper human respiratory tract}, series = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, journal = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, language = {en} } @misc{BirkenmaierDorniaLehleetal., author = {Birkenmaier, Clemens and Dornia, Christian and Lehle, Karla and Krenkel, Lars}, title = {Feasibility of detecting thrombotic deposits in membrane oxygenators using micro computed tomography}, series = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, journal = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, language = {en} } @article{BirkenmaierDorniaLehleetal., author = {Birkenmaier, Clemens and Dornia, Christian and Lehle, Karla and M{\"u}ller, Thomas and Gruber, Michael and Philipp, Alois and Krenkel, Lars}, title = {Analysis of Thrombotic Deposits in Extracorporeal Membrane Oxygenators by High-resolution Microcomputed Tomography: A Feasibility Study}, series = {ASAIO Journal / American Society for Artificial Internal Organs}, volume = {66}, journal = {ASAIO Journal / American Society for Artificial Internal Organs}, number = {8}, publisher = {Lippincott Williams \& Wilkins}, issn = {1538-943X}, doi = {10.1097/MAT.0000000000001089}, pages = {922 -- 928}, abstract = {Coagulative disorders, especially clotting during extracorporeal membrane oxygenation, are frequent complications. Direct visualization and analysis of deposits in membrane oxygenators using computed tomography (CT) may provide an insight into the underlying mechanisms causing thrombotic events. However, the already established multidetector CT1 (MDCT) method shows major limitations. Here, we demonstrate the feasibility of applying industrial micro-CT (μCT) to circumvent these restrictions. Three clinically used membrane oxygenators were investigated applying both MDCT and μCT. The scans were analyzed in terms of clot volume and local clot distribution. As validation, the clot volume was also determined from the fluid volume, which could be filled into the respective used oxygenator compared to a new device. In addition, cross-sectional CT images were compared with crosscut oxygenators. Based on the μCT findings, a morphological measure (sphericity) for assessing clot structures in membrane oxygenators is introduced. Furthermore, by comparing MDCT and μCT results, an augmentation of the MDCT method is proposed, which allows for improved clot volume determination in a clinical setting.}, language = {en} } @techreport{SteigerFoltanPhilippetal., type = {Working Paper}, author = {Steiger, Tamara and Foltan, Maik and Philipp, Alois and M{\"u}ller, Thomas and Gruber, Michael and Bredthauer, Andre and Krenkel, Lars and Birkenmaier, Clemens and Lehle, Karla}, title = {Accumulations of von Willebrand factor within ECMO oxygenators: Potential indicator of coagulation abnormalities in critically ill patients?}, abstract = {Clot formation within membrane oxygenators (MOs) remains a critical problem during extracorporeal membrane oxygenation (ECMO). The composition of the clots—in particular, the presence of von Willebrand factor (vWF)—may be an indicator for prevalent nonphysiological flow conditions, foreign body reactions, or coagulation abnormalities in critically ill patients. Mats of interwoven gas exchange fibers from randomly collected MOs (PLS, Maquet, Rastatt, Germany) of 21 patients were stained with antibodies (anti-vWF and anti-P-selectin) and counterstained with 4′,6-diamidino-2-phenylindole. The extent of vWF-loading was correlated with patient and technical data. While 12 MOs showed low vWF-loadings, 9 MOs showed high vWF-loading with highest accumulations close to crossing points of adjacent gas fibers. The presence and the extent of vWF-fibers/"cobwebs," leukocytes, platelet-leukocyte aggregates (PLAs), and P-selectin-positive platelet aggregates were independent of the extent of vWF-loading. However, the highly loaded MOs were obtained from patients with a significantly elevated SOFA score, severe thrombocytopenia, and persistent liver dysfunction. The coagulation abnormalities of these critically ill patients may cause an accumulation of the highly thrombogenic and elongated high-molecular-weight vWF multimers in the plasma which will be trapped in the MOs during the ECMO therapy.}, language = {en} } @misc{FriedrichRivoireScholzetal., author = {Friedrich, Janet and Rivoire, Julien and Scholz, Alexander-Wigbert K. and Wiegbert, and Terekov, Maxim and Kbrich, Rainer and Krenkel, Lars and Wagner, Claus and Schreiber, Laura Maria}, title = {Exploration of Gas Flow During High Frequency Oscillated Ventilation by 19F-Gas-MRI}, series = {Proceedings of the International Society for Magnetic Resonance in Medicine}, volume = {18}, journal = {Proceedings of the International Society for Magnetic Resonance in Medicine}, abstract = {To detect convective gas flow inside the large airways during high frequency oscillated ventilation (HFOV) the fluorinated contrast gas Heptafluoropropane was used for 19F-MRI. In a first study the comparison between constant flow measurements and Computational Fluid Dynamics (CFD) simulations provided a good agreement. In a following experiment oscillated flow was applied to a lung phantom consisting of ventilation bag and long pipe. The pressure wave inside the pipe was explored point-by-point and corresponding velocities were determined. With these experiments it could be shown for the first time that flow measurement during HFOV using fluorinated contrast gas is feasible.}, language = {en} } @misc{Krenkel, author = {Krenkel, Lars}, title = {Relevanz von Aerosolen im klinischen Kontext}, series = {Innovationstag Hygiene 2021, Continental Arena, Regensburg, Deutschland}, journal = {Innovationstag Hygiene 2021, Continental Arena, Regensburg, Deutschland}, language = {de} } @misc{StelzerRuettenKrenkel, author = {Stelzer, Vera and R{\"u}tten, Markus and Krenkel, Lars}, title = {Numerical Investigation of a 3D Dragonfly Wing Captured with a High-Resolution Micro-CT}, series = {8th European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS Congress 2022, 5-9 June 2022, Oslo, Norway}, journal = {8th European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS Congress 2022, 5-9 June 2022, Oslo, Norway}, abstract = {The special wing geometry of dragonflies consisting of veins and a membrane forming a corrugated profile leads to special aerodynamic characteristics. To capture the governing flow regimes of a dragonfly wing in detail, a realistic wing model has to be investigated. Therefore, this study aimed to analyze the aerodynamic characteristics of a 3D dragonfly wing reconstructed from a high-resolution micro-CT scan. Afterwards, a spatially high discretized mesh was generated using the mesh generator CENTAUR™ 14.5.0.2 (CentaurSoft, Austin, TX, US) to finally conduct Computational Fluid Dynamics (CFD) investigations in Fluent® 2020 R2 (ANSYS, Inc., Canonsburg, PA, US). Due to the small dimensions of the wing membrane, only the vein structure of a Camacinia Gigantea was captured at a micro-CT voxel size of 7 microns. The membrane was adapted and connected to the vein structure using a Boolean union operation. Occurring nconsistencies after combining the veins and the membrane were corrected using an adapted pymesh script [1]. As an initial study, only one quarter of the wing (outer wing section) was investigated to reduce the required computational effort. The resulting hybrid mesh consisting of 10 pseudo-structured prism layers along the wing surface and tetrahedra in the farfield area has 43 mio. nodes. The flow around the wing was considered to be incompressible and laminar using transient calculations. When the flow passes the vein structures, steady vortices occur in the corrugation valleys leading to recirculation zones. Therefore, the dragonfly wing resembles the profile of an airfoil. This leads to comparable lift coefficients of dragonfly wings and airfoil profiles at significantly reduced structural weight. The reconstructed geometry also included naturally occurring triangular prismlike serrated structures at the leading edge of the wing, which have comparable effects to micro vortex generators and might stabilize the recirculation zones. Further work aims to investigate the aerodynamic properties of a complete dragonfly wing during wing flapping.}, language = {en} } @misc{Krenkel, author = {Krenkel, Lars}, title = {Maskenpflicht f{\"u}r Aerosole - wie wir medizinisches Personal in der Pandemie sch{\"u}tzen}, series = {TRIOKON Digital 2021 : Zukunft Ostbayern, 29.09.2021, Weiden, Deutschland}, journal = {TRIOKON Digital 2021 : Zukunft Ostbayern, 29.09.2021, Weiden, Deutschland}, language = {de} } @misc{KrenkelMichelKeiletal., author = {Krenkel, Lars and Michel, Johanna and Keil, Niklas and Daschner, Jan}, title = {Experimental Investigation of Logitudinal Folds in Endotracheal Tube Cuffs and their Correlation to Silent Breathing}, series = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, journal = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, address = {G{\"o}ttingen}, organization = {Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt e.V. / Arbeitsgemeinschaft Str{\"o}mungen mit Abl{\"o}sung, AG STAB}, abstract = {Air leakage past High-Volume-Low-Pressure (HVLP) endotracheal tube (ETT) cuffs creates a potential infection risk for health care professionals during ventilation of patients suffering from contagious airborne diseases. However, unlike silent aspiration, a phenomenon where fluids enter the airways of intubated patients, the aspect of aerosol emergence through cuff folds -what we called accordingly "silent breathing" (SB)- has not been investigated in detail so far. This study investigates air leakage past HVLP cuffs with varying cuff pressures under realistic artificial breathing scenarios experimentally and in addition numerically. The focus was laid on the parametric investigation of the occurrence and furthermore on different influencing factors of silent breathing. The morphology of the folds responsible for the leakage was captured using high-resolution 3D microcomputed tomography (μCT). For the numerical investigations (Com-putational Fluid Dynamics - CFD), the commercial CFD Software package FLUENT 2021 R2 (ANSYS, Inc., Canonsburg, PA, US), as well as the DLR in-house research code THETA has been used.}, language = {en} } @misc{TauwaldQuadrioRuettenetal., author = {Tauwald, Sandra Melina and Quadrio, Maurizio and R{\"u}tten, Markus and Stemmer, Christian and Krenkel, Lars}, title = {High Spatial Resolution Tomo-PIV of the Nasopharynx Focussing on the Physiological Breathing Cycle}, series = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, journal = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, address = {G{\"o}ttingen}, organization = {Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt e.V. / Arbeitsgemeinschaft Str{\"o}mungen mit Abl{\"o}sung, AG STAB}, abstract = {Investigations of complex patient-specific flow in the nasopharynx requires high resolution numerical calculations validated by reliable experiments. When building the validation base and the benchmark of computational fluid dynamics, an experimental setup of the nasal airways was developed. The applied optical measurement technique of tomo-PIV supplies information on the governing flow field in three dimensions. This paper presents tomo-PIV measurements of the highly complex patient-specific geometry of the human trachea. A computertomographic scan of a person's head builds the basis of the experimental silicone model of the nasal airways. An optimised approach for precise refractive index matching avoids optical distortions even in highly complex non-free-of-sight 3D geometries. A linear-motor-driven pump generates breathing scenarios, based on measured breathing cycles. Adjusting of the CCD cameras' double-frame-rate PIV-Δt enables the detailed analysis of flow structures during different cycle phases. Merging regions of interest enables high spatial resolution acquisition of the flow field.}, language = {en} } @misc{StelzerTauwaldVielsmeieretal., author = {Stelzer, Vera and Tauwald, Sandra Melina and Vielsmeier, Veronika and Cieplik, Fabian and Kandulski, Arne and Schneider-Brachert, Wulf and Wuensch, Olaf and R{\"u}tten, Markus and Krenkel, Lars}, title = {Generation, Distribution, and Contagiousness of Surgical Smoke during Tracheotomies}, series = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, journal = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, address = {G{\"o}ttingen}, organization = {Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt e.V. / Arbeitsgemeinschaft Str{\"o}mungen mit Abl{\"o}sung, AG STAB}, abstract = {Surgical smoke has been a little discussed topic in the context of the current pandemic. Surgical smoke is generated during the cauterization of tissue with heat-generating devices and consists of 95\% water vapor and 5\% cellular debris in the form of particulate matter. In-vivo investigations are performed during tracheotomies where surgical smoke is produced during tissue electrocautery. Furthermore, in-vitro parametric studies to investigate the particle number and size distribution and the spatial distribution of surgical smoke with laser light sheet technique are conducted. The higher the power of the high-frequency-device the larger the particles in size and the higher the resulting particle counts. The images taken show the densest smoke at 40W with artificial saliva. The resulting characteristic size distribution, which may include viruses and bacterial components, confirms that the risk arising from surgical smoke should be considered. Furthermore, the experiments will provide the database for further numerical investigations.}, language = {en} } @article{SteigerFoltanPhilippetal., author = {Steiger, Tamara and Foltan, Maik and Philipp, Alois and M{\"u}ller, Thomas and Gruber, Michael and Bredthauer, Andre and Krenkel, Lars and Birkenmaier, Clemens and Lehle, Karla}, title = {Accumulations of von Willebrand factor within ECMO oxygenators: Potential indicator of coagulation abnormalities in critically ill patients?}, series = {Artificial Organs}, volume = {43}, journal = {Artificial Organs}, number = {11}, publisher = {Wiley}, address = {Hoboken}, issn = {1525-1594}, doi = {10.1111/aor.13513}, pages = {1065 -- 1076}, abstract = {Clot formation within membrane oxygenators (MOs) remains a critical problem during extracorporeal membrane oxygenation (ECMO). The composition of the clots-in particular, the presence of von Willebrand factor (vWF)-may be an indicator for prevalent nonphysiological flow conditions, foreign body reactions, or coagulation abnormalities in critically ill patients. Mats of interwoven gas exchange fibers from randomly collected MOs (PLS, Maquet, Rastatt, Germany) of 21 patients were stained with antibodies (anti-vWF and anti-P-selectin) and counterstained with 4 ',6-diamidino-2-phenylindole. The extent of vWF-loading was correlated with patient and technical data. While 12 MOs showed low vWF-loadings, 9 MOs showed high vWF-loading with highest accumulations close to crossing points of adjacent gas fibers. The presence and the extent of vWF-fibers/"cobwebs," leukocytes, platelet-leukocyte aggregates (PLAs), and P-selectin-positive platelet aggregates were independent of the extent of vWF-loading. However, the highly loaded MOs were obtained from patients with a significantly elevated SOFA score, severe thrombocytopenia, and persistent liver dysfunction. The coagulation abnormalities of these critically ill patients may cause an accumulation of the highly thrombogenic and elongated high-molecular-weight vWF multimers in the plasma which will be trapped in the MOs during the ECMO therapy.}, language = {en} } @misc{BirkenmaierKrenkel, author = {Birkenmaier, Clemens and Krenkel, Lars}, title = {Towards a realistic model of blood viscosity and coagulation in membrane oxygenators}, series = {6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) - ECCM 6; 7th European Conference on Computational Fluid Dynamics - ECFD 7 : Glasgow, Scotland, UK, June 11-15, 2018}, journal = {6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) - ECCM 6; 7th European Conference on Computational Fluid Dynamics - ECFD 7 : Glasgow, Scotland, UK, June 11-15, 2018}, abstract = {Modelling blood flow an shear induced coagulation in membraene oxygenators (MO) is challenging. The relevant geometry of oxygenator fibers (OF) and chaining threads is complex and spans several length scales. In relevant scales and regimes blood shows several significant non-Newtonian effects. Existing models are only capable of accounting for some, but not all relevant effects. Additionally, coagulation processes are influencing fluid properties and geometry significantly. Due to the enormous size of the discretised geometries highly detailed viscosity and coagulation properties of blodd flow in MOs. First step is to find a gemoetry dependent viscosity representation on basis of parametric micro channel experiments with anti-coagulated blood. Next step is a statistic coagulation model, based on micro channel experiments with human (re-calcified citrated) whole blood an evaluation of clinically used osygenators. Since shear rate dependent (i.e. viscosity dependet) coagulation in return influences the viscosity, a combined model with suitable implementation in a RANS framework is necessary. Towards this end, micro channel experiments with new and used single OFs triggering coagulation are performed. Structures of multimeric von Willebrand fibers (vWF), as indicator for shear induced coagulation, are compared to computed and measured flow conditions, using immunofluorescence microscopy, RANS-computations and µPIV, respectively. Preliminary examinations in clinically used MOs show good agreement between occurring structures of vWF, cell depositions and computed flow patterns (geometry form µCT-Scans). However, computed shear rates might be to low to actually trigger activation of vWF. The complex geometry of MOs results in huge meshes, which makes RANS with statistical modelling of viscosity and coagulation a reasonable approach. Towards this end, experimental data on micro channel level with evaluation on real application level is crucial. Especially regarding clotting processes, micro fluidic experiments are powerful research tool.}, language = {en} } @inproceedings{BirkenmaierSteigerPhilippetal., author = {Birkenmaier, Clemens and Steiger, Tamara and Philipp, Alois and Lehle, Karla and Krenkel, Lars}, title = {Flow-induced accumulations of von Willebrand factor inside oxygenators during extracorporeal life support therapy}, series = {Proceedings of 12th International Conference BIOMDLORE 2018, June 28-30, 2018, Białystok, Poland}, booktitle = {Proceedings of 12th International Conference BIOMDLORE 2018, June 28-30, 2018, Białystok, Poland}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-5386-2396-1}, doi = {10.1109/BIOMDLORE.2018.8467205}, pages = {3}, abstract = {BACKGROUND: Shear-induced conformational changes of von Willebrand factor (vWF) may be responsible for coagulation disorder and clot formation inside membrane oxygenators (MOs) during extracorporeal membrane oxygenation (ECMO) therapy. OBJECTIVE: The aim was to identify vWF structures inside clinically used MOs and employ computational fluid dynamics to verify the corresponding flow conditions. METHODS: Samples from gas exchange membranes (GEM) from MOs were analysed for accumulations of vWF and P-selectin-positive platelets using immunofluorescence techniques. Streamlines and shear rates of the flow around GEMs were computed using a laminar steady Reynolds-Averaged-Navier-Stokes approach. RESULTS: Most samples were colonized with equally distributed leukocytes, integrated in thin cobweb-like vWF-structures. Only 25 \% of the samples showed extended accumulations of vWF. Computed streamlines showed considerable cross flow between interconnected neighbouring channels. Stagnation points were non-symmetric and contact faces were washed around closely. The occurring maximum shear rates ranged from 2,500 to 3,000 1/s. CONCLUSIONS: If pronounced vWF structures are present, shape and extent match the flow computations well. Computed shear rates bear a critical degree of uncertainty due to the improper viscosity model. If flow conditions inside the MO were sufficient to affect vWF, a more consistent distribution of vWF across the samples should be present.}, language = {en} } @unpublished{BurgerBartschGradetal., author = {Burger, Moritz and Bartsch, Alexander and Grad, Marius and Esper, Lukas and Schultheiß, Ulrich and Noster, Ulf and Schratzenstaller, Thomas}, title = {Enhancement of laser cut edge quality of ultra-thin titanium grade 2 sheets by applying in-process approach using modulated Yb:YAG continuous wave fibre laser}, doi = {10.21203/rs.3.rs-2520041/v1}, abstract = {Titanium is used in many areas due to its excellent mechanical, biological and corrosion-resistant properties. Implants often have thin and filigree structures, providing an ideal application for laser fine cutting. In literature, the main focus is primarily on investigating and optimizing the parameters for titanium sheet thicknesses greater than 1 mm. Hence, in this study, the basic manufacturing parameters of laser power, cutting speed and laser pulsing of a 200 W modulated fibre laser are investigated for 0.15 mm thick titanium grade 2 sheets. A reproducible, continuous cut could be achieved using 90 W laserpower and 2 cutting-speed. Pulse pause variations between 85-335 μs in 50 μs steps and fixed pulse duration of 50 μs show that a minimum kerf width of 23.4 μm, as well as a minimum cut edge roughness Rz of 3.59 μm, is achieved at the lowest pulse pause. An increase in roughness towards the laser exit side, independent of the laser pulse pause, was found and discussed. The results provide initial process parameters for cutting thin titanium sheets and thus provide the basis for further investigations, such as the influence of cutting gas pressure and composition on the cut edge.}, language = {en} } @unpublished{GradHaagHahnetal., author = {Grad, Marius and Haag, Lydia and Hahn, Konstantin and Schultheiß, Ulrich and Esper, Lukas and Noster, Ulf}, title = {Influence of carbon content on the formation of TiC at diffusion bonded titanium-steel interface}, publisher = {Elsevier}, doi = {10.2139/ssrn.4261928}, abstract = {Hot pressing of pure Ti and various carbon steels in a temperature range of 950 - 1050 °C creates an up to 9 μm thick compound layer of TiC at the Ti/ steel interface. The calculation of the activation energy for layer formation is 126.5 - 136.7 kJ/mol, independent of the steels carbon content. As the carbon content of the steel increases, the layer thickness also increases, which provides enormous potential for the surface modification of Ti/ Ti-alloys.}, language = {en} } @inproceedings{MarinkovicGalkaMeissner, author = {Marinkovic, Minja and Galka, Stefan and Meißner, Sebastian}, title = {Digital Twins for Internal Transport Systems: Use Cases, Functions, and System Architecture}, series = {Proceedings of the 56th Hawaii International Conference on System Sciences: January 3-6, 2023, Maui, Hawaii, USA}, booktitle = {Proceedings of the 56th Hawaii International Conference on System Sciences: January 3-6, 2023, Maui, Hawaii, USA}, publisher = {University of Hawaiʻi at Mānoa}, address = {Honolulu, HI}, isbn = {978-0-9981331-6-4}, pages = {1195 -- 1204}, abstract = {Internal transport systems are an essential part of intralogistics in production and distribution facilities. These are characterized by a variety of technologies as well as a multitude of interactions with other processes, such as warehouse, picking, and production processes. Therefore, resource planning and control of these systems is complex, especially for discontinuous conveyors. In this task, users can be supported by Digital Twins for decision-making, as they are suitable for investigating both future system states and possible actions. However, relevant use cases that are generally applicable across sectors as well as a generic system architecture for Digital Twins for resource planning and process control of in-plant transport systems have not yet been sufficiently investigated. In this paper, use cases are presented, relevant functions defined, and, finally, a generic functional and a logical reference architecture described. This is conducted with the design science in information systems research method together with a Systems Engineering approach. The use cases are determined at industrial partners of the research project TwInTraSys, which explores Digital Twins for the planning and control of internal transport systems. They are generalized and, thus, also applicable to other production and distribution facilities in different sectors. Further, the reference architecture can provide a basis for the successful implementation of the Digital Twin.}, language = {en} } @article{MaiwaldHierl, author = {Maiwald, Frederik and Hierl, Stefan}, title = {Absorber-free laser transmission welding of transparent polymers}, series = {Laser Systems Europe}, volume = {50}, journal = {Laser Systems Europe}, number = {Spring 2021}, publisher = {Europa Science}, address = {Cambridge}, language = {en} } @inproceedings{KotzStapfBecke, author = {Kotz, Oliver and Stapf, Matthias and Becke, Mark}, title = {GPU-Based Task Specific Evaluation of the Dynamic Performance of a 6DOF Manipulator}, series = {Intelligent Robotics and Applications. 8th International Conference, ICIRA 2015, Portsmouth, UK, August 24-27, 2015, Proceedings, Part II}, booktitle = {Intelligent Robotics and Applications. 8th International Conference, ICIRA 2015, Portsmouth, UK, August 24-27, 2015, Proceedings, Part II}, publisher = {Springer}, address = {Cham}, doi = {10.1007/978-3-319-22876-1_30}, pages = {345 -- 357}, abstract = {This paper addresses the problem of properly placing a given task in the manipulator workspace by a heuristic and numeric approach. Thus, the task is placed relatively to the manipulator for each element of the discretized workspace and the required joint torques are determined. The results are are by a torque-based optimization criterion. The modularity of this approach ensures general applicability on various systems and tasks while the high computational effort is treated by GPU parallelization. The method is presented for a given 6DOF manipulator and a highly dynamic trajectory. The resulting interactive map of the manipulator workspace gives an overview of the task dependent dynamic performance, detailed evaluation of certain solutions will show the dexterity of the proposed approach.}, language = {en} } @article{MikhaeilGadererDawoud, author = {Mikhaeil, Makram and Gaderer, Matthias and Dawoud, Belal}, title = {On the application of adsorber plate heat exchangers in thermally driven chillers}, series = {Applied Thermal Engineering}, volume = {220}, journal = {Applied Thermal Engineering}, publisher = {Elsevier}, doi = {10.1016/j.applthermaleng.2022.119713}, abstract = {The effect of both heat and mass transfer characteristic lengths (HTCL, MTCL) of two different adsorber plate heat exchangers (APHE), for application in an adsorption chiller, on the adsorption and desorption kinetics is investigated. Three representative test frames (TF1-TF3) are prepared to examine small-scale adsorbent samples of the microporous silica gel (Siogel of Oker-Chemie, Germany) applying the volumetric large-temperature-jump methodology at different operating conditions. Based on the obtained kinetic data, an analytical model has been developed to predict the specific cooling power (SCP) and the coefficient of performance (COP) of a single-bed adsorption chiller comprising the studied APHEs. It turned out that, within the tested range of HTCL and MTCL, it can be concluded that, the adsorption kinetics are mainly influenced by the MTCL, while the desorption kinetics are dominated by the HTCL of the adsorbent domain. Applying Siogel as loose pellets inside a newly introduced APHE results in of 423.3 and 182.7 W⋅kg-1, at the evaporator temperatures of 15 °C and 5 °C, respectively. Herein, the condenser and adsorber-end temperatures amount to 30 °C and the desorption-end temperature to 90 °C. The corresponding s amount to 0.50 and 0.40, respectively, which represent quite promising results for further design optimizations.}, language = {en} } @inproceedings{ArrietaCastroWeberRill, author = {Arrieta Castro, Abel and Weber, Hans Ingo and Rill, Georg}, title = {Design an integrate vehicle control based-on hierarchical architecture for improve the performance of ground vehicles}, series = {COBEM2015 : 23rd ABCM International Congress of Mechanical Engineering, December 6-11, 2015, Rio de Janeiro, RJ, Brazi}, booktitle = {COBEM2015 : 23rd ABCM International Congress of Mechanical Engineering, December 6-11, 2015, Rio de Janeiro, RJ, Brazi}, organization = {Associa{\c{c}}{\~a}o Brasileira de Engenharia e Ci{\^e}ncias Mec{\^a}nicas}, doi = {10.20906/cps/cob-2015-1970}, language = {en} } @article{SchmidtPenzkoferBachmaieretal., author = {Schmidt, Ulf and Penzkofer, Rainer and Bachmaier, Samuel and Augat, Peter}, title = {Implant Material and Design Alter Construct Stiffness in Distal Femur Locking Plate Fixation: A Pilot Study}, series = {Clinical Orthopaedics and Related Research®}, volume = {471}, journal = {Clinical Orthopaedics and Related Research®}, number = {9}, publisher = {The Association of Bone and Joint Surgeons}, doi = {10.1007/s11999-013-2867-0}, pages = {2808 -- 2814}, abstract = {BACKGROUND: Construct stiffness affects healing of bones fixed with locking plates. However, variable construct stiffness reported in the literature may be attributable to differing test configurations and direct comparisons may clarify these differences. QUESTIONS/PURPOSES: We therefore asked whether different distal femur locking plate systems and constructs will lead to different (1) axial and rotational stiffness and (2) fatigue under cyclic loading. METHODS: We investigated four plate systems for distal femur fixation (AxSOS, LCP, PERI-LOC, POLYAX) of differing designs and materials using bone substitutes in a distal femur fracture model (OTA/AO 33-A3). We created six constructs of each of the four plating systems. Stiffness under static and cyclic loading and fatigue under cyclic loading were measured. RESULTS: Mean construct stiffness under axial loading was highest for AxSOS (100.8 N/mm) followed by PERI-LOC (80.8 N/mm) and LCP (62.6 N/mm). POLYAX construct stiffness testing showed the lowest stiffness (51.7 N/mm) with 50\% stiffness of AxSOS construct testing. Mean construct stiffness under torsional loading was similar in the group of AxSOS and PERI-LOC (3.40 Nm/degree versus 3.15 Nm/degree) and in the group of LCP and POLYAX (2.63 Nm/degree versus 2.56 Nm/degree). The fourth load level of > 75,000 cycles was reached by three of six AxSOS, three of six POLYAX, and two of six PERI-LOC constructs. All others including all LCP constructs failed earlier. CONCLUSIONS: Implant design and material of new-generation distal femur locking plate systems leads to a wide range of differences in construct stiffness. CLINICAL RELEVANCE: Assuming construct stiffness affects fracture healing, these data may influence surgical decision-making in choosing an implant system.}, language = {en} } @inproceedings{FriedrichFeldmannKrenkeletal., author = {Friedrich, Janet and Feldmann, Daniel and Krenkel, Lars and Wagner, Claus and Schreiber, Laura Maria}, title = {19F Gas Flow Measurement of C3F7H During Constant Flow and High Frequency Oscillatory Ventilation}, series = {Discovery, innovation \& application - advancing mr for improved health : ISMRM 21st Annual Meeting \& Exhibition ; SMRT 22nd Annual Meeting Salt Lake City, Utah, USA 20-26 April 2013}, volume = {21}, booktitle = {Discovery, innovation \& application - advancing mr for improved health : ISMRM 21st Annual Meeting \& Exhibition ; SMRT 22nd Annual Meeting Salt Lake City, Utah, USA 20-26 April 2013}, organization = {International Society for Magnetic Resonance in Medicine}, abstract = {The aim of the current study is the development of MRI methods that enable the investigation of gas flow mechanisms during high frequency oscillatory ventilation. This work includes flow measurements during three constant flows (19.9, 30.6 and 41.4 L min-1) and the comparison to direct numerical simulations (DNS) using a second-order-acurate finite-volume method and to data measured with a volume flow meter. 19F-MRI, DNS and flow meter data are in good agreement. Flow measurements during HFOV of 4 Hz were successfully performed and velocity profiles could be recorded at different phases of the ventilation cycle.}, language = {en} } @article{GoldhackerAlSubariAlBaddaietal., author = {Goldhacker, Markus and Al-Subari, Karema and Al-Baddai, Saad and Tom{\´e}, Ana Maria and Faltermeier, Rupert and Lang, Elmar Wolfgang}, title = {EMDLAB: A toolbox for analysis of single-trial EEG dynamics using empirical mode decomposition}, series = {Journal of Neuroscience Methods}, volume = {253}, journal = {Journal of Neuroscience Methods}, number = {September}, publisher = {Elsevier}, address = {AMsterdam}, doi = {10.1016/j.jneumeth.2015.06.020}, pages = {193 -- 205}, abstract = {Background: Empirical mode decomposition (EMD) is an empirical data decomposition technique. Recently there is growing interest in applying EMD in the biomedical field. New method: EMDLAB is an extensible plug-in for the EEGLAB toolbox, which is an open software environment for electrophysiological data analysis. Results: EMDLAB can be used to perform, easily and effectively, four common types of EMD: plain EMD, ensemble EMD (EEMD), weighted sliding EMD (wSEMD) and multivariate EMD (MEMD) on EEG data. In addition, EMDLAB is a user-friendly toolbox and closely implemented in the EEGLAB toolbox. Comparison with existing methods: EMDLAB gains an advantage over other open-source toolboxes by exploiting the advantageous visualization capabilities of EEGLAB for extracted intrinsic mode functions (IMFs) and Event-Related Modes (ERMs) of the signal. Conclusions: EMDLAB is a reliable, efficient, and automated solution for extracting and visualizing the extracted IMFs and ERMs by EMD algorithms in EEG study.}, language = {en} } @inproceedings{NiedersteinerPohltSchlegl, author = {Niedersteiner, Sascha and Pohlt, Clemens and Schlegl, Thomas}, title = {Smart Workbench: A Multimodal and Bidirectional Assistance System for Industrial Application}, series = {IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society, 09.-12.11.2015, Yokohama, Japan}, booktitle = {IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society, 09.-12.11.2015, Yokohama, Japan}, publisher = {IEEE}, address = {Piscataway, N.J.}, isbn = {978-1-4799-1762-4}, doi = {10.1109/iecon.2015.7392549}, abstract = {Manual tasks in industrial production are often monotonous, leading to a decrease in concentration and motivation of the worker and thus to deficiencies in the products. With quality as well as performance requirements getting more and more stringent, workers need additional support by their work environment. We developed a novel approach providing worker assistance and inline quality assurance for manual workplaces. The prototypical system Smart Workbench (SWoB) uses a multimodal sensor interface consisting of a 3D depth sensor in combination with a 2D camera to control quality aspects of the product and track the work progress. The bidirectional flow of information is handled via an image processing driven gestural interface and the displaying of advice directly on the work surface. In this paper the developed system is introduced and the current state of evaluating its industrial usage with a manual quality control and packaging task reported.}, language = {en} } @article{WagnerPinskyMalhotra, author = {Wagner, Marcus and Pinsky, Peter M. and Malhotra, Manish}, title = {A multiple-frequency partial-field method for exterior acoustics based on Pad{\´e} via lanczos approximants}, series = {Proceedings of the ASME Noise Control and Acoustics Division - 2001 : presented at the 2001 ASME International Mechanical Engineering Congress and Exposition, November 11 - 16, 2001, New York, New York}, journal = {Proceedings of the ASME Noise Control and Acoustics Division - 2001 : presented at the 2001 ASME International Mechanical Engineering Congress and Exposition, November 11 - 16, 2001, New York, New York}, number = {28}, publisher = {ASME}, address = {New York, NY}, isbn = {0-7918-3551-0}, doi = {10.1115/IMECE2001/NCA-23524}, pages = {229 -- 234}, abstract = {A solution methodology is introduced for the efficient computation of the acoustic field over restricted domains and for a frequency window. Typically, such partial field solutions include, for example, surfaces enclosing the radiating structure or even single points in the computational domain. The multiple-frequency partial-field (MFPF) method starts out by reformulating the finite element matrix system into a suitable shifted form. The DtN map is used as a radiation boundary condition and is interpreted as a low rank update of the matrix problem. The shifted standard form is then approximated by a rational matrix-valued Pad{\´e} approximant and solved simultaneously over a frequency range. To obtain the Pad{\´e} approximation, a banded unsymmetric Lanczos process is applied on the standard shifted form exploiting the matrix Pad{\´e}-via-Lanczos connection. Numerical examples show the feasibility of the outlined procedure.}, language = {en} } @misc{AlSubariAlBaddaiTomeetal., author = {Al-Subari, Karema and Al-Baddai, Saad and Tom{\´e}, Ana Maria and Goldhacker, Markus and Faltermeier, Rupert and Lang, Elmar Wolfgang}, title = {EMDLAB-toolbox- tutorial video}, language = {en} } @incollection{Galka, author = {Galka, Stefan}, title = {Planung und Auswahl von Kommissioniersystemen}, series = {MTM in einer globalisierten Wirtschaft : Arbeitsprozesse systematisch gestalten und optimieren}, booktitle = {MTM in einer globalisierten Wirtschaft : Arbeitsprozesse systematisch gestalten und optimieren}, editor = {Britzke, Bernd}, publisher = {mi-Wirtschaftsbuch Finanzbuch-Verl.}, address = {M{\"u}nchen}, isbn = {978-3-86880-091-3}, pages = {201 -- 220}, language = {de} } @inproceedings{GerschSchulzKral, author = {Gersch, Sebastian and Schulz, Carsten and Kral, Christopher}, title = {Verifizierung der Prozessstabilit{\"a}t einer konstruierten WAAM-Anlage zum Induzieren von Eigenspannungen in generativ gefertigten Strukturen}, series = {9. Mitteldeutsches Forum - 3D-Druck in der Anwendung: 29. Juni 2022, Jena}, booktitle = {9. Mitteldeutsches Forum - 3D-Druck in der Anwendung: 29. Juni 2022, Jena}, doi = {10.35096/othr/pub-5600}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-56006}, abstract = {Heutzutage werden Strukturen h{\"a}ufig aufwendig konstruiert und nachtr{\"a}glich mithilfe von numerischen Verfahren optimiert. Dennoch kommt es zu erheblichen Sch{\"a}den infolge von Erm{\"u}dungsbr{\"u}chen bei wechselnd beanspruchten Bauteilen. Ein Großteil dieser Sch{\"a}den hat den Ursprung in den im Inneren herrschenden Spannungszust{\"a}nden, den sogenannten Eigenspannungen. Diese Eigenspannungen heben sich innerhalb des Bauteils auf und f{\"u}hren zu keiner Formabweichung des Bauteils, weswegen diese Spannungen in Form und Lage nur schwer detektierbar sind und sich h{\"a}ufig negativ auf die Betriebsfestigkeit von Strukturen auswirken. Mithilfe neuartiger numerischer Methoden k{\"o}nnen thermomechanische Simulationen angefertigt und Verformungen, sowie Spannungszust{\"a}nde abgeleitet werden. Durch diese Optionen ergeben sich neue Anwendungen, die das Potenzial von Fertigungsverfahren in Hinblick auf die Ausnutzung spezieller Eigenschaften neu er{\"o}ffnen. Durch die geschickte Anwendung und Vernetzung der Simulation mit der Fertigung k{\"o}nnen Eigenspannungen gezielt in Lage und Richtung schon w{\"a}hrend der Produktion des Bauteils eingebracht werden. Im theoretischen Vergleich zu konventionell gefertigten Bauteilen entstehen Strukturen, die hinsichtlich ihrer Bauteillebensdauer optimiert sind.}, language = {de} } @inproceedings{GalkaGuenthnerUlbrich, author = {Galka, Stefan and G{\"u}nthner, Willibald A. and Ulbrich, Alexander}, title = {Planning of order-picking-systems with support of discrete simulation}, series = {Logistics and Supply Chain Management: Deutsch-Russische Perspektiven. Proceedings of the 5th German-Russian Logistics Workshop (DR-LOG10)}, booktitle = {Logistics and Supply Chain Management: Deutsch-Russische Perspektiven. Proceedings of the 5th German-Russian Logistics Workshop (DR-LOG10)}, language = {en} } @article{PlankRosengarthSchmalhoferetal., author = {Plank, Tina and Rosengarth, Katharina and Schmalhofer, Carolin and Goldhacker, Markus and Brandl-R{\"u}hle, Sabine and Greenlee, Mark W.}, title = {Perceptual learning in patients with macular degeneration}, series = {Frontiers in psychology}, volume = {5}, journal = {Frontiers in psychology}, publisher = {Frontiers Research Foundation}, address = {Lausanne}, issn = {1664-1078}, doi = {10.3389/fpsyg.2014.01189}, pages = {1 -- 14}, abstract = {Patients with age-related macular degeneration (AMD) or hereditary macular dystrophies (JMD) rely on an efficient use of their peripheral visual field. We trained eight AMD and five JMD patients to perform a texture-discrimination task (TDT) at their preferred retinal locus (PRL) used for fixation. Six training sessions of approximately one hour duration were conducted over a period of approximately 3 weeks. Before, during and after training twelve patients and twelve age-matched controls (the data from two controls had to be discarded later) took part in three functional magnetic resonance imaging (fMRI) sessions to assess training-related changes in the BOLD response in early visual cortex. Patients benefited from the training measurements as indexed by significant decrease (p = 0.001) in the stimulus onset asynchrony (SOA) between the presentation of the texture target on background and the visual mask, and in a significant location specific effect of the PRL with respect to hit rate (p = 0.014). The following trends were observed: (i) improvement in Vernier acuity for an eccentric line-bisection task; (ii) positive correlation between the development of BOLD signals in early visual cortex and initial fixation stability (r = 0.531); (iii) positive correlation between the increase in task performance and initial fixation stability (r = 0.730). The first two trends were non-significant, whereas the third trend was significant at p = 0.014, Bonferroni corrected. Consequently, our exploratory study suggests that training on the TDT can enhance eccentric vision in patients with central vision loss. This enhancement is accompanied by a modest alteration in the BOLD response in early visual cortex.}, language = {en} } @article{GoldhackerRosengarthAnstisetal., author = {Goldhacker, Markus and Rosengarth, Katharina and Anstis, Stuart and Wirth, Anna and Plank, Tina and Greenlee, Mark W.}, title = {FMRI evidence for perceptual filling-in in patients with macular dystrophy}, series = {Perception}, volume = {42}, journal = {Perception}, issn = {1468-4233}, pages = {72 -- 73}, language = {en} } @inproceedings{KrenkelPennecotLenzetal., author = {Krenkel, Lars and Pennecot, Julien and Lenz, Christian and Feldmann, Daniel and Wagner, Claus}, title = {Optimierung der Hochfrequenz-Oszillationsventilation mittels str{\"o}mungsmechanischer Methoden und kontrastgasgest{\"u}tzter Magnetresonanztomografie - Teilprojekt: Rekonstruktion von Geometrien aus medizinischen Bilddaten und Erstellung von Modellen f{\"u}r experimentelle Str{\"o}mungsuntersuchungen}, series = {Laseranwendung in der Medizin, Erfassen und Verarbeiten kardiovaskul{\"a}rer Signale, protektive Beatmungskonzepte : 3. Dresdner Medizintechnik-Symposium - mit DFG-Forschungsschwerpunkt Protektive Beatmungskonzepte, 6. bis 9. Dezember 2010, Dresden}, booktitle = {Laseranwendung in der Medizin, Erfassen und Verarbeiten kardiovaskul{\"a}rer Signale, protektive Beatmungskonzepte : 3. Dresdner Medizintechnik-Symposium - mit DFG-Forschungsschwerpunkt Protektive Beatmungskonzepte, 6. bis 9. Dezember 2010, Dresden}, editor = {F{\"u}ssel, Jens and Koch, Edmund and Malberg, Hagen}, publisher = {TUDpress}, address = {Dresden}, isbn = {978-3-942710-02-2}, pages = {107 -- 114}, abstract = {Der vorliegende Artikel skizziert die neu entwickelte Prozesskette f{\"u}r detailgenaue Rekonstruktion von Geometrien anhand medizinischer Bilddaten sowie die Herstellung von transparenten Modellen f{\"u}r experimentelle Untersuchungen mit bildgebenden Str{\"o}mungsmessverfahren. Die Geometriedaten und Modelle werden f{\"u}r systematische Untersuchungen der komplexen Transportvorg{\"a}nge in den Atemwegen bei k{\"u}nstlicher Beatmung mittels Hochfrequenzoszillationsventilation (HFOV) verwendet.}, language = {en} } @article{GreenleeRosengarthSchmalhoferetal., author = {Greenlee, Mark W. and Rosengarth, Katharina and Schmalhofer, Carolin and Goldhacker, Markus and Brandl-R{\"u}hle, Sabine and Plank, Tina}, title = {Perceptual learning in patients with central scotomata due to hereditary and age-related macular dystrophy}, series = {Journal of Vision}, volume = {14}, journal = {Journal of Vision}, number = {10}, publisher = {ARVO}, issn = {1468-4233}, doi = {10.1167/14.10.666}, abstract = {Hereditary and age-related forms of macular dystrophy (MD) are characterized by loss of cone function in the fovea, leading to central scotomata and eccentric fixation at the so-called preferred retinal locus (PRL). We investigated whether perceptual learning enhances visual abilities at the PRL. We also determined the neural correlates (3-Tesla fMRI) of learning success. Twelve MD patients (eight with age-related macular dystrophy, four with hereditary macular dystrophies) were trained on a texture discrimination task (TDT) over six days. Patients underwent three fMRI sessions (before, during and after training) while performing the TDT (target at PRL or opposite PRL). Reading speed, visual acuity (Vernier task) and contrast sensitivity were also assessed before and after training. With one exception, all patients showed improved performance (i.e. significant decrease in stimulus onset asynchronies and reaction times, significant increase in hit rates) on the TDT. Eight patients also showed moderate increases in reading speed, six patients showed improved thresholds in contrast sensitivity and nine patients showed improved thresholds in a vernier visual acuity task after TDT training. We found an increase in BOLD response in the projections zone of the PRL in the primary visual cortex in nine of twelve patients after training. The change in fMRI signal correlated (r = .8; p = .02) with the patients{\^a}€™ performance enhancements when the target was in the PRL. The results suggest that perceptual learning can enhance eccentric vision and cortical processing in MD patients.}, language = {en} } @techreport{Krenkel, author = {Krenkel, Lars}, title = {Investigation of the impact of vortex generators on the shock/boundary-layer interaction}, issn = {1434-8454}, abstract = {Comprehensive experimental and numerical parameter studies on the impact of isolated vortex generator pairs and complex vortex generator arrays onto a strong shock-/boundary layer interaction are presented within the context of this thesis. The effects of vortices, especially as they interact with each other are discussed in terms of their impact on the boundary layer development, the shock characteristics and the overall aerodynamic performance of the aerofoil. The presented results have been obtained from wind tunnel experiments with a simple flat plate with superimposed pressure gradient as well as with a more comprehensive model of a supercritical transonic aerofoil. In addition complex numerical parameter studies on a supercritical aerofoil in free stream conditions have been conducted. This work is designed for gaining a better understanding of the fundamental mechanisms of vortex generator/shock/boundary-layer interaction in order to achieve improved flight performance in terms of drag reduction, avoidance or at least postponement of separation onset and shock oscillation as well as lift improvement by application of optimised vortex generator configurations.}, language = {en} } @book{Krenkel, author = {Krenkel, Lars}, title = {Untersuchung des Einflusses von Wirbelgeneratoren auf die Stoß-/Grenzschicht-Wechselwirkung}, publisher = {Rheinisch-Westf{\"a}lische Technische Hochschule Aachen}, address = {Aachen}, issn = {1434-8454}, abstract = {Im Rahmen dieser Arbeit werden experimentelle und numerische Parameterstudien von einzelnen Wirbelgeneratorpaaren und komplexeren Wirbelgeneratoranordnungen bez{\"u}glich ihres Einflusses auf eine starke Stoß-/Grenzschicht-Wechselwirkung vorgestellt. Dabei werden die Einfl{\"u}sse von Wirbeln, insbesondere die Auswirkungen ihrer Wechselwirkungen untereinander, auf das Grenzschichtverhalten, die Stoßcharakteristik und insgesamt auf die aerodynamische Leistung des betrachteten Profils diskutiert. Dazu wurden sowohl Windkanalversuche am einfachen Modell einer ebenen Platte mit aufgepr{\"a}gtem Druckgradienten sowie an einem Modell eines superkritischen transsonischen Profils durchgef{\"u}hrt. Erg{\"a}nzend wurden komplexe nume-rische Parameteruntersuchungen an einem Profil in freier Anstr{\"o}mung ausgef{\"u}hrt. Es ist das Ziel, ein besse-res Verst{\"a}ndnis der Mechanismen der Wirbelgenerator-/Stoß-/Grenzschicht-Wechselwirkung zu gewinnen, um durch optimierte Anwendung von Wirbelgeneratoren eine Verbesserung der Flugleistungen erzielen zu k{\"o}nnen. Die Schwerpunkte liegen dabei auf der Reduktion des Widerstandes, der Vermeidung bzw. Verz{\"o}ge-rung von Str{\"o}mungsabl{\"o}sung und Stoßschwingung sowie auf der Erh{\"o}hung des Auftriebs.}, language = {de} } @inproceedings{GoldhackerTomeGreenleeetal., author = {Goldhacker, Markus and Tom{\´e}, Ana Maria and Greenlee, Mark W. and Lang, Elmar Wolfgang}, title = {Early meta-level: deeper understanding of connectivity-states and consequences for state definition}, series = {21st Annual Meeting of the Organization for Human Brain Mapping, June 14-18, 2015, Honolulu, Hawaii}, booktitle = {21st Annual Meeting of the Organization for Human Brain Mapping, June 14-18, 2015, Honolulu, Hawaii}, publisher = {Academic Press}, address = {San Diego, CA}, doi = {10.13140/RG.2.1.2561.3929}, language = {en} } @inproceedings{KrenkelWagnerWolfetal., author = {Krenkel, Lars and Wagner, Claus and Wolf, Ursula and Scholz, Alexander-Wigbert K. and Terekhov, Maxim and Rivoire, Julien and Schreiber, W.}, title = {Protective Artificial Lung Ventilation: Impact of an Endotracheal Tube on the Flow in a Generic Trachea}, series = {New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008}, editor = {Hirschel, Ernst Heinrich and Schr{\"o}der, Wolfgang and Fujii, Kozo and Haase, Werner and Leer, Bram and Leschziner, Michael A. and Pandolfi, Maurizio and Periaux, Jacques and Rizzi, Arthur and Roux, Bernard and Shokin, Yurii I. and Dillmann, Andreas and Heller, Gerd and Klaas, Michael and Kreplin, Hans-Peter and Nitsche, Wolfgang}, publisher = {Springer Berlin Heidelberg}, address = {Berlin, Heidelberg}, isbn = {978-3-642-14242-0}, doi = {10.1007/978-3-642-14243-7_62}, pages = {505 -- 512}, abstract = {Computational Fluid Dynamics (CFD) and experimental investigations on a generic model of the trachea have been carried out focusing on the impact of an endotracheal tube (ETT) on the resulting flow regime. It could be shown that detailed modelling of the airway management devices is essential for proper flow prediction, but secondary details as Murphy Eyes can be neglected. Models with bending and connector promote the formation of stronger secondary flows and disturbances which persist for a longer time.}, language = {en} } @incollection{RuettenKrenkel, author = {R{\"u}tten, Markus and Krenkel, Lars}, title = {Vortex-Generator Pairs for Vortex-Induced Heat-Transfer Enhancement in Heat-Exchanger Channels}, series = {New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008}, editor = {Hirschel, Ernst Heinrich and Schr{\"o}der, Wolfgang and Fujii, Kozo and Haase, Werner and Leer, Bram and Leschziner, Michael A. and Pandolfi, Maurizio and Periaux, Jacques and Rizzi, Arthur and Roux, Bernard and Shokin, Yurii I. and Dillmann, Andreas and Heller, Gerd and Klaas, Michael and Kreplin, Hans-Peter and Nitsche, Wolfgang}, publisher = {Springer Berlin Heidelberg}, address = {Berlin, Heidelberg}, isbn = {978-3-642-14242-0}, doi = {10.1007/978-3-642-14243-7_68}, pages = {555 -- 562}, abstract = {The objective of the presented work is to investigate possibilities for increasing the heattransfer in heat-exchanger channels for aircraft applications by using flow-manipulating devices. Focal point of the investigation are different arrangements of vortex-generator pairs within a generic heat-exchanger channel. The DLR URANS CFD solver THETA has been used to carry out numerical simulations of the laminar flow within a rectangular channel with integrated vortex generators. In particular, the analysis of the interaction of generated vortices with the stratified thermal boundary layer, the impact of vortical flow structures on heated walls and the enforced mixed-convection flow is of special interest. The final goal is the evaluation of the applicability of oppositely arranged vortex-generator pairs for the enhancement of vortex-induced heat-transfer.}, language = {en} } @inproceedings{MarkusRuettenKrenkelKessler, author = {Markus R{\"u}tten, and Krenkel, Lars and Kessler, Roland}, title = {Secondary Flow Effects as Physical Mechanism of Molecular Species Transport in Highly Oscillating Generic-Trachea Flows}, series = {83rd Annual Scientific Conference of the International Association of Applied Mathematics and Mechanics, 26.-30. M{\"a}rz 2012, Darmstadt, Germany}, booktitle = {83rd Annual Scientific Conference of the International Association of Applied Mathematics and Mechanics, 26.-30. M{\"a}rz 2012, Darmstadt, Germany}, abstract = {The high frequency oscillation artificial respiration technique is often the last hope for patients to survive highly damaged lung tissue. The mortality can significantly be reduced. In comparison to conventional artificial respiration the applied volume flow rate and pressure is significantly lowered in order to avoid further damaging of lung tissue and remaining intact alveolae. However, the physical mechanism of transport of oxygen to the aeriols under high frequency oscillation is not well understood. In the upper part of the lung convection is dominant, in contrast, the gas exchange in the lower parts of the lung is mainly driven by diffusion. It is not clear how associated gradients of concentrations of different molecular species are then achieved. Highly oscillating fluid flows has been a long research topic in fluid dynamics. It is known that oscillating pressure fluctuations are able to induce secondary flows, in particular, in curved ducts and pipes. The question is, whether the trachea enforces the generation of secondary flow by its kidney like cross section geometry. The influence of molecular species of different densities onto the formation of secondary flows and the convectional transport within the trachea is investigated. In order to clarify the physical mechanisms behind flow simulations have been conducted by using state of the art CFD techniques.}, language = {en} } @incollection{ScholzKrenkelTerekhovetal., author = {Scholz, Alexander-Wigbert K. and Krenkel, Lars and Terekhov, Maxim and Friedrich, Janet and Rivoire, Julien and K{\"o}brich, Rainer and Wolf, Ursula and Kalthoff, Daniel and David, Matthias and Wagner, Claus and Schreiber, Laura Maria}, title = {Magnetic Resonance Imaging and Computational Fluid Dynamics of High Frequency Oscillatory Ventilation (HFOV)}, series = {Fundamental Medical and Engineering Investigations on Protective Artificial Respiration}, volume = {116}, booktitle = {Fundamental Medical and Engineering Investigations on Protective Artificial Respiration}, editor = {Hirschel, Ernst Heinrich and Schr{\"o}der, Wolfgang and Fujii, Kozo and Haase, Werner and Leer, Bram and Leschziner, Michael A. and Pandolfi, Maurizio and Periaux, Jacques and Rizzi, Arthur and Roux, Bernard and Shokin, Yurii I. and Klaas, Michael and Koch, Edmund and Schr{\"o}der, Wolfgang}, publisher = {Springer}, address = {Berlin, Heidelberg}, isbn = {978-3-642-20325-1}, doi = {10.1007/978-3-642-20326-8_7}, pages = {107 -- 128}, abstract = {In order to better understand the mechanisms of gas transport during High Frequency Oscillatory Ventilation (HFOV) Magnetic Resonance Imaging (MRI) with contrast gases and numerical flow simulations based on Computational Fluid Dynamics(CFD) methods are performed. Validation of these new techniques is conducted by comparing the results obtained with simplified models of the trachea and a first lung bifurcation as well as in a cast model of the upper central airways with results achieved from conventional fluid mechanical measurement techniques like e.g. Laser Doppler Anemometry (LDA). Further it is demonstrated that MRI of experimental HFOV is feasible and that Hyperpolarized 3He allows for imaging the gas re-distribution inside the lung. Finally, numerical results of oscillatory flow in a 3rd generation model of the lung as well as the impact of endotracheal tubes on the flow regime development in a trachea model are presented.}, language = {en} } @article{GoldhackerRosengarthPlanketal., author = {Goldhacker, Markus and Rosengarth, Katharina and Plank, Tina and Greenlee, Mark W.}, title = {The effect of feedback on performance and brain activation during perceptual learning}, series = {Vision research}, volume = {99}, journal = {Vision research}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1878-5646}, doi = {10.1016/j.visres.2013.11.010}, pages = {99 -- 110}, abstract = {We investigated the role of informative feedback on the neural correlates of perceptual learning in a coherent-motion detection paradigm. Stimulus displays consisted of four patches of moving dots briefly (500 ms) presented simultaneously, one patch in each visual quadrant. The coherence level was varied in the target patch from near threshold to high, while the other three patches contained only noise. The participants judged whether coherent motion was present or absent in the target patch. To guarantee central fixation, a secondary RSVP digit-detection task was performed at fixation. Over six training sessions subjects learned to detect coherent motion in a predefined quadrant (i.e., the learned location). Half of our subjects were randomly assigned to the feedback group, where they received informative feedback after each response during training, whereas the other group received non-informative feedback during training that a response button was pressed. We investigated whether the presence of informative feedback during training had an influence on the learning success and on the resulting BOLD response. Behavioral data of 24 subjects showed improved performance with increasing practice. Informative feedback promoted learning for motion displays with high coherence levels, whereas it had little effect on learning for displays with near-threshold coherence levels. Learning enhanced fMRI responses in early visual cortex and motion-sensitive area MT+ and these changes were most pronounced for high coherence levels. Activation in the insular and cingulate cortex was mainly influenced by coherence level and trained location. We conclude that feedback modulates behavioral performance and, to a lesser extent, brain activation in areas responsible for monitoring perceptual learning.}, language = {en} } @misc{GreenleeAnstisRosengarthetal., author = {Greenlee, Mark W. and Anstis, Stuart and Rosengarth, Katharina and Goldhacker, Markus and Brandl-R{\"u}hle, Sabine and Plank, Tina}, title = {Neural correlates of perceptual filling-in: fMRI evidence in the foveal projection zone of patients with central scotoma}, series = {Journal of Vision / Vision Sciences Society Annual Meeting Abstract}, volume = {12}, journal = {Journal of Vision / Vision Sciences Society Annual Meeting Abstract}, number = {9}, publisher = {ARVO}, issn = {1534-7362}, doi = {10.1167/12.9.1303}, abstract = {Patients with juvenile retinal dystrophy often report that they are unaware of their central scotoma, suggesting the presence of perceptual filling-in. We used functional Magnetic Resonance Imaging (fMRI) to determine possible neural correlates of perceptual filling-in in patients with retinal distrophy and clinically established central scotoma in both eyes. The data of 5 patients (Stargardt disease, cone-rod dystrophy; mean age 45 yrs; scotoma diameter 10-20°) and of 5 normally sighted controls were analyzed. Fixation behaviour and perimetry were measured with a Nidek microperimeter. Magnetic resonance imaging was performed using a Siemens 3T Allegra scanner. We stimulated the central visual field (30 deg) with a vertically oriented, low spatial frequency (1 c/deg) high-contrast sinewave grating that was either a) continuous, or b) was interrupted by a central grey disk. The disk was either slightly larger than the scotoma (detectable on 75\% of trials) or slightly smaller (detectable on 25\% of trials). To control for attention, an eccentric fixation task was performed during scanning. Data were analyzed using SPM8 (GLM with ROI analysis to obtain percent signal change for foveal projection zone). Results: for all patients, the BOLD signal in the foveal projection area was significantly higher for the small disk (i.e., condition leading to complete filling-in) than for the large disk (i.e., no filling-in). This effect was absent in the control subjects. Our findings support the existence of an active neural process that leads to filling-in in patients with central visual field scotomata.}, language = {en} } @article{WagnerPinskyMalhotra, author = {Wagner, Marcus and Pinsky, Peter M. and Malhotra, Manish}, title = {Application of Pad{\´e} via Lanczos approximations for efficient multifrequency solution of Helmholtz problems}, series = {Journal of the Acoustical Society of America}, volume = {113}, journal = {Journal of the Acoustical Society of America}, number = {1}, publisher = {American Inst. of Physics}, issn = {1520-8524}, doi = {10.1121/1.1514932}, pages = {313 -- 319}, abstract = {This paper addresses the efficient solution of acoustic problems in which the primary interest is obtaining the solution only on restricted portions of the domain but over a wide range of frequencies. The exterior acoustics boundary value problem is approximated using the finite element method in combination with the Dirichlet-to-Neumann (DtN) map. The restriction domain problem is formally posed in transfer function form based on the finite element solution. In order to obtain the solution over a range of frequencies, a matrix-valued Pad{\´e} approximation of the transfer function is employed, using a two-sided block Lanczos algorithm. This approach provides a stable and efficient representation of the Pad{\´e} approximation. In order to apply the algorithm, it is necessary to reformulate the transfer function due to the frequency dependency in the nonreflecting boundary condition. This is illustrated for the case of the DtN boundary condition, but there is no restriction on the approach which can also be applied to other radiation boundary conditions. Numerical tests confirm that the approach offers significant computational speed-up.}, language = {en} } @article{WagnerPinskyOberaietal., author = {Wagner, Marcus and Pinsky, Peter M. and Oberai, Assad and Malhotra, Manish}, title = {A Krylov subspace projection method for simultaneous solution of Helmholtz problems at multiple frequencies}, series = {Computer Methods in Applied Mechanics and Engineering}, volume = {192}, journal = {Computer Methods in Applied Mechanics and Engineering}, number = {41-42}, publisher = {Elsevier}, doi = {10.1016/S0045-7825(03)00429-8}, pages = {4609 -- 4640}, abstract = {A Krylov subspace projection method which provides simultaneous solutions of the Helmholtz equation at multiple frequencies in one solution step is presented. The projector is obtained with an unsymmetric block Lanczos algorithm applied to a transfer function derived from a finite element discretization. This approach is equivalent to a matrix-valued Pad{\´e} approximation of the transfer function. The proposed method is an extension of the formulation presented in [J. Comput. Acoust. 8 (2000) 223] to unsymmetric systems and allows the treatment of a much wider range of practical problems, including near-field and fluid-structure interaction computations}, language = {en} } @inproceedings{UcsnikGradingerNosteretal., author = {Ucsnik, Stephan A. and Gradinger, Rudolf and Noster, Ulf and Pahr, Dieter H.}, title = {Finite element based optimization of a novel metal-composite-joint}, series = {1st EUCOMAS, European Conference on Materials and Structures in Aerospace, Conference Berlin, May 26 - 27, 2008 }, booktitle = {1st EUCOMAS, European Conference on Materials and Structures in Aerospace, Conference Berlin, May 26 - 27, 2008 }, publisher = {VDI-Verlag}, address = {D{\"u}sseldorf}, issn = {0083-5560}, pages = {371 -- 379}, abstract = {Aerospace and automotive industries employ three main techniques to set up joints between metal and fibre reinforced plastics parts (FRP); adhesive bonding, mechanical fastening with rives/bolts and a hybrid combination. A new joint technique has been developed to combine the two advantageous mechanisms form-closure and adhesion in a fibre-friendly way. Prior is established through metal structures (pins) which are perpendicularly welded onto metal surfaces with an arc-welding-process. They intrude into the FRP during lay-up and therefore set up a first connection. The composite-matrix is responsible for latter adhesive bonding and final form closure. Finite-element-analyses of cylindrically shaped joints are carried out to get detailed knowledge of the influence of parameters like pin-number, pin-position, pin-height, pin-form sleeve-geometry, and stiffness behaviour. Long calculation times of 3D-models lead to the introduction of a corresponding 2D-axisymmetric-model which is used to run parameter-studies within a reasonable time. For this novel technique the combination of fibre-friendly form closure and adhesive bonding of interface plays a major role. A well selected amount of vertical reinforcements, their placement and geometrical dimensions will lead to a stiffer joint. Goal is to minimize fibre-deletion and overlap length to improve load-transfer and joint-strength, to reduce weight in high-strength-applications as well as the avoidance of safety rivets.}, language = {en} } @article{GoldhackerFellnerVolbergetal., author = {Goldhacker, Markus and Fellner, Marie-Christin and Volberg, G. and Mullinger, K. J. and Greenlee, Mark W. and Hanslmayr, Simon}, title = {Spurious correlations in simultaneous EEG-fMRI driven by in-scanner movement}, series = {NeuroImage}, volume = {133}, journal = {NeuroImage}, number = {June}, publisher = {Elsevier}, doi = {10.1016/j.neuroimage.2016.03.031}, pages = {354 -- 366}, abstract = {Simultaneous EEG-fMRI provides an increasingly attractive research tool to investigate cognitive processes with high temporal and spatial resolution. However, artifacts in EEG data introduced by the MR scanner still remain a major obstacle. This study, employing commonly used artifact correction steps, shows that head motion, one overlooked major source of artifacts in EEG-fMRI data, can cause plausible EEG effects and EEG-BOLD correlations. Specifically, low-frequency EEG (< 20 Hz) is strongly correlated with in-scanner movement. Accordingly, minor head motion (< 0.2 mm) induces spurious effects in a twofold manner: Small differences in task-correlated motion elicit spurious low-frequency effects, and, as motion concurrently influences fMRI data, EEG-BOLD correlations closely match motion-fMRI correlations. We demonstrate these effects in a memory encoding experiment showing that obtained theta power (~ 3-7 Hz) effects and channel-level theta-BOLD correlations reflect motion in the scanner. These findings highlight an important caveat that needs to be addressed by future EEG-fMRI studies.}, language = {en} } @article{VoyerPeterlechnerNoster, author = {Voyer, Joel and Peterlechner, Christian and Noster, Ulf}, title = {Flame sprayed Al-12Si coatings for the improvement of the adhesion of composite casting profiles}, series = {Journal of Thermal Spray Technology}, volume = {17}, journal = {Journal of Thermal Spray Technology}, number = {5-6}, publisher = {Springer}, address = {Boston, Mass.}, issn = {1544-1016}, doi = {https://doi.org/10.1007/s11666-008-9235-8}, pages = {824 -- 830}, abstract = {In this study, flame sprayed Al-12Si coatings were produced on the surface of inlays (aluminum profiles) of composite castings parts. The aim was to enhance the strength between the joining partners inlay and cast. Due to the high surface roughness and the presence of pores in the coatings, combined with the formation of an intermetallic phase at the interface, the adhesion of flame sprayed inlays could be enhanced by a factor of 2 compared to blank inlays and by a factor of 1.3 when compared to sand-blasted inlays. However, results also show that gaps are present, mostly at the interface between the inlays and the flame sprayed coatings, and these gaps have a negative effect on the joining strength of the composite casting parts. Therefore, optimizing the adhesion of the coating on the Al profiles via an improvement in both the sand-blasting and the flame spraying parameters would be beneficial for further enhancement of the adhesion of composite casting parts.}, language = {de} } @inproceedings{MilaevRuiderSchlegl, author = {Milaev, Johannes and Ruider, Martin and Schlegl, Thomas}, title = {Entwicklung eines Experimentalsystems zur Validierung adaptiver Regelungen mit einem OEM-Steuerger{\"a}t}, series = {Tagungsband AALE 2014 : das Forum f{\"u}r Fachleute der Automatisierungstechnik aus Hochschulen und Wirtschaft ; 11. Fachkonferenz, Regensburg}, booktitle = {Tagungsband AALE 2014 : das Forum f{\"u}r Fachleute der Automatisierungstechnik aus Hochschulen und Wirtschaft ; 11. Fachkonferenz, Regensburg}, publisher = {Deutscher Industrieverlag}, address = {M{\"u}nchen}, isbn = {978-3-8356-7142-3}, pages = {241 -- 250}, abstract = {Im Rahmen des Kooperationsprojektes "ACES" (Integrated Adaption of Linear Controllers for Embedded Systems) ist ein Pr{\"u}fstand zur Validierung adaptiver Regelungen entwickelt und aufgebaut worden, der das dynamische Verhalten eines Kfz-Antriebstrangs aufweist. Ziel ist es, verschiedene Adaptionsverfahren auf ihre Einsetzbarkeit in OEM-Steuerger{\"a}ten, die im Automotive-Bereich auf breiter Basis verwendet werden, kosteng{\"u}nstig testen zu k{\"o}nnen. Das Problem der aktiven Schwingungsd{\"a}mpfung in Kfz-Antriebsstr{\"a}ngen mit unbekannten und ver{\"a}nderlichen mechanischen Parametern stellt eine Pilotanwendung dar. Ein leicht anpassbarer mechanischer Pr{\"u}fstand dient hierbei als vereinfachtes Modell eines Antriebstrangs. Dieser ist Bestandteil eitles Experimentalsystems mit einer informationstechnischen Architektur, die einen Betrieb engebetteter Regelungssysteme auf verschiedenen Plattformen gestattet. Das flexible mechanische und informationstechnische Design des Experimentalsystems gestattet die Variation von Parametern der zu regelnden Applikation durch leicht austauschbare mechanische Komponenten und gezielte Einbringung von St{\"o}rgr{\"o}ßen. Zudem kann die Berechnung der Regelungsarchitektur auf einem Industrie-PC oder einem Steuerger{\"a}t erfolgen. Weitere Vorteile des entwickelten Experimentalsystems sind die Ber{\"u}cksichtigung von Effekten, die aus dem Verhalten realer Sensoren und der CAN-basierten Signal{\"u}bertragung entstehen. Insbesondere der Einfluss von Wortbreite und Latenz {\"u}bertragener Signale auf die Adaption von Regelungen kann mit Hilfe des vorgestellten Experimentalsystems eingehend untersucht werden.}, language = {de} } @article{KuepperArtmannPischingeretal., author = {K{\"u}pper, Carsten and Artmann, Christina and Pischinger, Stefan and Rabl, Hans-Peter}, title = {Lube-Oil Dilution of GDI Engines with Ethanol Fuels}, series = {Auto Tech Review}, volume = {3}, journal = {Auto Tech Review}, number = {3}, publisher = {Springer India}, address = {New Delhi}, doi = {10.1365/s40112-014-0570-5}, pages = {30 -- 35}, language = {en} } @article{AntenLebsanftKraussetal., author = {Anten, Kerstin and Lebsanft, Markus and Krauß, M. and Noster, Ulf and Scholtes, Berthold}, title = {Einfluss von Randschichtzustand und Haltezeit auf die thermische Erm{\"u}dung der Magnesiumbasislegierung AZ31}, series = {Materialwissenschaft und Werkstofftechnik}, volume = {43}, journal = {Materialwissenschaft und Werkstofftechnik}, number = {12}, publisher = {Wiley}, pages = {993 -- 1000}, abstract = {Die vorliegende Arbeit befasst sich mit Untersuchungen zur thermischen Erm{\"u}dung der Magnesiumbasislegierung AZ31 im Temperaturbereich zwischen +50°C und +290°C. Die Experimente erfolgten unter konstanter Totaldeformation (out-of-phase-Beanspruchung) und es wurde der Verlauf der Spannungsamplitude sowie der plastischen Dehnungsamplitude {\"u}ber die Zahl der Temperaturzyklen ermittelt. Insbesondere wurde der Einfluss einer mechanischen Oberfl{\"a}chenbehandlung (Festwalzen) sowie von Haltezeiten auf den Verlauf der Sch{\"a}digung untersucht. In beiden F{\"a}llen konnte kein signifikanter Unterschied zu unbehandelten Proben bzw. Beanspruchungen ohne Haltezeit festgestellt werden, welches auf die Wechselwirkungen zwischen Verformungs- und Rekristallisationsprozessen bei der thermischen Erm{\"u}dung zur{\"u}ckzuf{\"u}hren ist.}, language = {en} } @article{HofmannHierl, author = {Hofmann, A. and Hierl, Stefan}, title = {Kontrolliertes Laserdurchstrahlschweißen}, series = {Kunststoffe}, volume = {95}, journal = {Kunststoffe}, number = {6}, publisher = {Hanser}, pages = {36 -- 38}, abstract = {Obwohl das Laserdurchstrahlschweißen sehr reproduzierbar arbeitet, k{\"o}nnen Fehler aus den Vorprozessen Compoundieren, Spritzgießen etc. das Schweißergebnis negativ beeinflussen. Dem Anwender steht inzwischen eine breite Palette an Prozess{\"u}berwachungsmethoden zur Verf{\"u}gung, um eine gleich bleibende Produktqualit{\"a}t zu erzielen.}, language = {de} } @article{KuepperArtmannPischingeretal., author = {K{\"u}pper, Carsten and Artmann, Christina and Pischinger, Stefan and Rabl, Hans-Peter}, title = {Schmier{\"o}lverd{\"u}nnung von direkteinspritzenden Ottomotoren unter Kaltstartrandbedingungen}, series = {MTZ - Motortechnische Zeitschrift}, volume = {74}, journal = {MTZ - Motortechnische Zeitschrift}, number = {9}, publisher = {Springer Vieweg}, address = {Wiesbaden}, doi = {10.1007/s35146-013-0208-1}, pages = {710 -- 715}, language = {de} } @article{Lermer, author = {Lermer, Josef}, title = {Optimierter Antriebsstrang und neuartiges Differenzial f{\"u}r einen Formula-Student-Rennwagen}, series = {ATZ-Extra}, volume = {20}, journal = {ATZ-Extra}, number = {Suppl 5}, publisher = {Springer Fachmedien GmbH}, doi = {10.1007/s35778-015-0071-4}, pages = {34 -- 39}, language = {de} } @inproceedings{JuijermAltenbergerNosteretal., author = {Juijerm, Patiphan and Altenberger, Igor and Noster, Ulf and Scholtes, Berthold}, title = {Residual stress relaxation and cyclic deformation behavior of deep rolled AlMg4.5Mn (AA5083) at elevated temperatures}, series = {Materials Science Forum}, volume = {490-491}, booktitle = {Materials Science Forum}, publisher = {Trans Tech Publications}, doi = {10.4028/www.scientific.net/MSF.490-491.436}, pages = {436 -- 441}, abstract = {The cyclic deformation behavior of deep rolled and polished aluminium wrought alloy AlMg4,5Mn in the temperature range 20-300°C has been investigated. Results of quasistatic tension and compression tests of untreated specimens in the temperature range 20-300°C are presented. To characterize the fatigue behavior for stress-controlled tests as a function of test temperature, s-n curves, cyclic deformations curves and mean strains as a function of number of cycles are given. The residual stress- and work hardening states near the surface of deep rolled aluminium alloy AlMg4.5Mn before and after fatigue tests were investigated by X-ray diffraction methods. The investigated AlMn4.5Mn aluminium alloy shows cyclic hardening until fracture at all stress amplitudes in stress-controlled fatigue tests at 25-150°C. With increasing temperature the deformation behavior shifts from cyclic hardening to cyclic softening. Below a certain stress amplitude at a given temperature deep rolling led to a reduction of the plastic strain amplitude as compared to the untreated state through cyclically stable near-surface work hardening as indicated by stable FWHM-values. This reduction in plastic strain amplitude is associated with enhanced fatigue lives. The effectiveness of deep rolling is governed by the cyclic and thermal stability of near-surface work hardening rather than macroscopic compressive residual stresses. Since near-surface work hardening is known to retard crack initiation, deep rolling is also effective in temperature- and stress ranges where macroscopic compressive residual stresses have relaxed almost completely, but where near-surface work hardening prevails. Above certain stress amplitudes and temperatures, deep rolling has no beneficial effect on the fatigue behavior of AlMg4.5Mn. This is a consequence of instable near-surface microstructures, especially instable near-surface work hardening.}, language = {en} } @inproceedings{Galka, author = {Galka, Stefan}, title = {Untersuchung von Auftragsfreigabestrategien f{\"u}r mehrzonige Kommissioniersysteme im Online-Lebensmittelhandel}, series = {ASIM SST 2022 Proceedings Langbeitr{\"a}ge, 26. ASIM Symposium Simulationstechnik: 25.07.-27.07.2022, TU Wien}, volume = {2022}, booktitle = {ASIM SST 2022 Proceedings Langbeitr{\"a}ge, 26. ASIM Symposium Simulationstechnik: 25.07.-27.07.2022, TU Wien}, publisher = {ARGESIM Verlag}, address = {Wien}, organization = {Gesellschaft f{\"u}r Informatik. Arbeitskreis f{\"u}r Simulation in der Fertigungstechnik}, isbn = {978-3-901608-97-1}, doi = {10.11128/arep.20.a2021}, pages = {23 -- 30}, abstract = {This paper briefly presents the challenges for order control and release of multi-zone order picking systems. On the one hand, the order control must ensure that all orders are processed on time, and on the other hand, the space requirements (buffer) and the utilisation of the zones must be considered. Within the framework of a case study, different strategies for order release were developed. The paper shortly describes the ideas of the strategies and presents results of a case-based simulative evaluation of the strategies. The findings of the simulation study are the basis for the development of a digital twin for the operational control of multi-zone picking systems.}, subject = {Simulation}, language = {de} } @article{GalkaFollathBross, author = {Galka, Stefan and Follath, Alexander and Bross, Florian}, title = {Vorgehensmodell zur Erstellung Digitaler Zwillinge f{\"u}r Produktion und Logistik}, series = {Zeitschrift f{\"u}r wirtschaftlichen Fabrikbetrieb}, volume = {117}, journal = {Zeitschrift f{\"u}r wirtschaftlichen Fabrikbetrieb}, number = {11}, editor = {Bauer, Wilhelm and Volk, Wolfram and Z{\"a}h, Michael}, publisher = {De Gruyter}, address = {Berlin}, doi = {10.1515/zwf-2022-1127}, pages = {691 -- 696}, abstract = {Der Digitale Zwilling (DZ) ist ein wichtiger Bestandteil der Industrie 4.0 und erm{\"o}glicht Anwendungen wie Predictive Maintenance, virtuelles Prototyping oder die Steuerung von Produktions- und Logistikprozessen. Herausforderungen bei der Entwicklung des Digitalen Zwillings entstehen durch fehlende Struktur und Standards. Mit diesem Beitrag soll ein Vorgehensmodell f{\"u}r die Erstellung eines Digitalen Zwillings im Bereich der Produktion und Logistik aufgezeigt werden. Das Vorgehensmodell hilft bei der Einordnung, f{\"u}r welche Anwendungsf{\"a}lle ein Digitaler Zwilling entwickelt werden kann, welche Schritte bei einer Umsetzung erfolgen m{\"u}ssen, und gibt einen {\"U}berblick {\"u}ber die Voraussetzungen und Komplexit{\"a}t bei der Entwicklung. Das zentrale Element bildet dabei die zielgerichtete Aufbereitung und Analyse der zugrunde liegenden Daten mittels des in der Industrie etablierten Vorgehensmodell CRISP-DM.}, language = {de} } @article{KettnerNosterKilianetal., author = {Kettner, Michael and Noster, Ulf and Kilian, Helmut and Gradinger, Rudolf and Kuehlein, Wolfgang and Drevenstedt, Armin and Stadler, Franz and Ladstaetter, Elisabeth and Lutz, Andreas}, title = {The InnMag project - Processing Mg for civil aircraft application}, series = {Advanced Engineering Materials}, volume = {9}, journal = {Advanced Engineering Materials}, number = {9}, publisher = {Wiley}, doi = {10.1002/adem.200700143}, pages = {813 -- 819}, abstract = {In the context of the "InnMag" project, partners from industry and science are co-operating to investigate the issues involved in adapting established production processes to the material Mg. The project's aim is to further the deployment of Mg interior parts in civil aircraft. The project covers every production step, from alloy selection, Mg ingot melting, alloying, direct chill casting, extruding, machining, surface treatment and component assembly. This paper discusses the project's targets and the results arrived at so far, particularly in the areas of direct chill casting and extrusion.}, language = {en} } @article{ManarancheHornberger, author = {Manaranche, Claire and Hornberger, Helga}, title = {A proposal for the classification of precious dental alloys according to their resistance to corrosion based on the iso 10271 standard}, series = {European Cells and Materials}, volume = {5}, journal = {European Cells and Materials}, number = {SUPPL. 1}, publisher = {Univ. of Wales}, address = {Aberystwyth, Wales}, pages = {34 -- 36}, abstract = {A lot of dental alloys are available on the market. Among these alloys, there are the conventional alloys, the so called casting alloys used without ceramics, the bonding alloys used with high fusing ceramics and the universal alloys used without or with low fusing ceramics. It is im portant to know the physical and mechanical properties of these materials but also their biocompatibility and their resistance to corrosion. Dental alloys are generally placed in the mouth for many years, they must not induce adverse biological reactions such as gingival swelling and erythema, mucosal pain and lichenoid reactions. Although these troubles are often caused not by the materials itself (1, 2), they can be induced by the metallic ions released during their corrosion. In order to decrease the risks to the health, it is necessary to study the corrosion of the dental alloys. Currently, the ISO 10271 Standard (3), describes 3 different corrosion tests: a static immersion test (chemical corrosion), an electrochemic al test and a tarnish test. However, there are no indications yet about the possible interpretation of test results. In this paper, we propose a method to compare and classify the dental alloys in relation to their chemical and electrochemical corrosion results. METHODS: The material tested are pure metals such as gold, palladium, silver, copper and zinc as well as dental alloys which are commercially sold (see Table 1). 54 different materials have been tested. A minimum of four samples of each material were tested by electrochemic al corrosio n and a minimum of three in chemical test. The samples were cast and prepared as indicated by the manufacturer and by the ISO 10271. For the electrochemical test, the samples are in the form of disks 11 mm in diameter. They are tested with a potentiostat/galvanostat Voltalab Model 21. For the chemical test, the samples are rectangular with the dimensions 35X10X1.7 mm. The solution used and the operating conditions are described in the ISO 10271. The concentration of metallic ions released is measured by Induced Coupled Plasma}, language = {en} } @article{AuerSchieblIversenetal., author = {Auer, Simon and Schiebl, Jonas and Iversen, Kristoffer and Subhash Chander, Divyaksh and Damsgaard, Michael and Dendorfer, Sebastian}, title = {Biomechanical assessment of the design and efficiency of occupational exoskeletons with the AnyBody Modeling System}, series = {Zeitschrift f{\"u}r Arbeitswissenschaften}, volume = {76}, journal = {Zeitschrift f{\"u}r Arbeitswissenschaften}, number = {4}, publisher = {Springer Nature}, doi = {10.1007/s41449-022-00336-4}, pages = {440 -- 449}, abstract = {Exoskeletons were invented over 100 years ago but have only become popular in the last two decades, especially in the working industry as they can decrease work-related loads significantly. The most often used exoskeletons are for the lower back and shoulder since these are commonly affected body regions. All devices have in common that their purpose is to reduce internal loads of vulnerable body regions. Nevertheless, there is still little understanding on how biomechanical loading in the human body changes when exoskeletons are used. Therefore, further analyses are needed. A promising candidate for these are musculoskeletal models, which are based on an inverse dynamics approach and can calculate external parameters such as ground reaction forces or other interaction forces as well as internal parameters such as joint reaction forces or muscle activities. The various examples in the literature show that these models are increasingly used for assessing the biomechanical effects of exoskeletons on the human body. Furthermore, musculoskeletal models can calculate biomechanical loadings of humans with and without exoskeletons for all kinds of applications and allow an evaluation of their purpose. Practical Relevance: This article highlights the possibilities of musculoskeletal models for assessing the design and efficiency of occupational exoskeletons. Several practical use cases are described along with distinct descriptions of common implications of musculoskeletal and exoskeleton modeling.}, language = {en} }